Preparation of BaTiO_{3} Films on Si Substrate with MgO Buffer Layer by RF Magnetron Sputtering

Wen-Ching Shih, Yuan-Sung Liang, and Mu-Shiang Wu — 2008-09-19T12:10:00+09:00

Authors: Wen-Ching Shih, Yuan-Sung Liang, and Mu-Shiang Wu
Highly (002)- or (200)-oriented BaTiO_{3} thin films were successfully grown on a Si substrate with a MgO buffer layer by RF magnetron sputtering. The deposition parameters need to be stringently controlled in order to grow BaTiO_{3} films with good crystallinity. The sputtering parameters such as substrate temperature, RF power, gas flow ratio, and deposition pressure were varied to obtain the optimum deposition conditions for the BaTiO_{3} films. The as-deposited films were characterized by X-ray diffraction analysis and atomic force microscopy to analyze their crystalline structure and surface morphology. The full width at half maximum intensity of the BaTiO_{3} (002) or (200) peak of the sample fabricated under the optimum deposition parameters was only 0.28°. The surface roughness of the BaTiO_{3} films was about 3.2 nm. The results could be useful in the integration of ferroelectric and semiconductor devices on the same Si substrate.

Fabrication of BaTiO_{3} Thin Films Using Modified Chemical Solutions and Sintering Method

Kiyotaka Tanaka, Kazuyuki Suzuki, and Kazumi Kato — 2008-09-19T12:10:00+09:00

Authors: Kiyotaka Tanaka, Kazuyuki Suzuki, and Kazumi Kato
BaTiO_{3} thin films were fabricated at 650 °C by single sintering using additive-free and diethanolamine (DEA)-modified alkoxide solutions. The BaTiO_{3} thin films derived from the DEA-modified solution had a flat surface and an rms roughness below 2.5 nm. The grain size on Pt/Ti/SiO_{2}/Si substrates single-sintered at 650 °C for 100 min was estimated to be about 34 to 43 nm. We succeeded in obtaining the electric properties of Pt/BaTiO_{3}/Pt capacitors by single sintering at 650 °C for 1 min. The dielectric constant ε_{r} and dielectric loss tanδ at 1 MHz were 110 and 0.05, respectively. On the other hand, the grain size on SiO_{2}/Si substrates single-sintered at 650 °C for 100 min reached about 55 to 62 nm. For the thickness and Fourier-transform infrared (FT-IR) spectra of the gel films, it was found that the thickness of the gel films at around 200 °C derived from the DEA-modified solution became abnormally thick and that the intermediate compounds generated during the decomposition of DEA remained in the gel films.

Oxygen Sensing Properties of SrTiO_{3} Thin Films

Toru Hara, Takashi Ishiguro, Naoki Wakiya, and Kazuo Shinozaki — 2008-09-19T12:10:00+09:00

Authors: Toru Hara, Takashi Ishiguro, Naoki Wakiya, and Kazuo Shinozaki
The oxygen sensing properties of SrTiO_{3}-based thin films have been investigated at room temperature. First, nondoped SrTiO_{3} was investigated. Although such a material is highly sensitive, its electrical resistance was too high and not feasible for practical use. Donor (Nb^{5+}) could lower the resistance of SrTiO_{3}; however, the sensitivity was lost. UV-light irradiation or t_{2}-type acceptor (Cr^{3+}) doping could lower the resistance and yet maintain the sensitivity. In contrast to t_{2}-type acceptor doping, e-type acceptor (Fe^{3+}) doping could lower the resistance; however, the sensitivity was lost. In this paper, we discuss the phenomena from the viewpoint of polaron-controlled carrier conduction.

Fabrication of (Ba_{0.6},Sr_{0.4})TiO_{3} Thick Films by Aerosol Deposition Method for Application to Embedded Multilayered Capacitor Structures

Daniel Popovici, Hiroki Tsuda, and Jun Akedo — 2008-09-19T12:10:00+09:00

Authors: Daniel Popovici, Hiroki Tsuda, and Jun Akedo
(Ba_{0.6},Sr_{0.4})TiO_{3} thick films were fabricated on Pt/Ti/SiO_{2}/Si, stainless steel (SUS) and Cu substrates by aerosol deposition (AD) technique. The effect of substrate on physical and electrical properties of the fabricated films has been studied. The AD-formed films have an average grain size of 15.9 to 18.3 nm, substrate having a small effect on its value. Strain is affected by the substrate selection and it is smallest when Cu has been selected as the metal substrate for AD of (Ba_{0.6},Sr_{0.4})TiO_{3} powder, having a value of 0.00552. The leakage current of (Ba_{0.6},Sr_{0.4})TiO_{3} thick films deposited on Cu substrates is smaller that for films deposited on Pt/Ti/SiO_{2}/Si and SUS substrates being less than 10^{-7} A/cm^{2} at 200 kV/cm applied electric field. The above results indicate that Cu is a good candidate for metallization in multilayered capacitor structure fabrication when AD technique is used for dielectric film formation.

Effect of Interface Structure on Electrical Properties of (Ba,Sr)TiO_{3} Thin Films on Glazed Alumina Substrate

2008-09-19T12:10:00+09:00

Authors: Takashi Nozaka, Yoji Mizutani, Bhakdisongkhram Gun, Masahiro Echizen, Takashi Nishida, Hiroaki Takeda, Kiyoshi Uchiyama, and Tadashi Shiosaki
We examined the impact that the electrode/(Ba,Sr)TiO_{3} (BST) interface structures have on electric properties by investigating the electrical conduction mechanism of the BST thin-film capacitors with Pt and Au top electrodes. The BST thin films were prepared on the Pt bottom electrode/glazed Al_{2}O_{3} substrate by chemical solution deposition (CSD). The dielectric property of the as-deposited Pt/BST/Pt capacitor had a large frequency dispersion and the leakage current properties deteriorated because the Pt top electrode/BST interface structure is rough. However, by post-annealing for 30 min at 400 °C after the top electrode was deposited, the frequency and temperature properties improved. The Schottky barrier height at the Pt top electrode/BST interface was 1.03 eV and that at the Au/BST interface was 0.73 eV, which indicated that its electrical conduction mechanism depends on the Schottky emission model. The dielectric constant, tanδ, and tunability of the Au/BST/Pt capacitor are 200, 0.0178, and 53.7% (at 214 kV/cm, 6.0 V), respectively, which showed excellent dielectric properties. This suggests that high-quality BST films for application to tunable microwave devices can be formed on a very inexpensive glazed Al_{2}O_{3} substrate.

Microwave Tunable Devices Composed of Coplanar Waveguide Line with (Ba_{0.6},Sr_{0.4})TiO_{3}/Au/Cr/(Ba_{0.6},Sr_{0.4})TiO_{3} Sandwich Structure

2008-09-19T12:10:00+09:00

Authors: Minoru Noda, Shigeyuki Watanabe, Kousuke Seki, Takeshi Kanashima, and Masanori Okuyama
A new coplanar waveguide (Ba,Sr)TiO_{3}/Au/Cr/(Ba,Sr)TiO_{3} sandwich structure was designed and fabricated as a microwave tunable device. (Ba,Sr)TiO_{3} (BST) (60/40) thin films were prepared on a (100) MgO substrate by metal–organic-decomposition (MOD). The tunability increased from 10.4 to 13.3% with the addition of sandwich structure (upper BST film thickness, 600 nm) at 1 MHz, while the dielectric loss in the structure was 0.006. The microwave propagation characteristics of the sandwich structure and the conventional single BST film coplanar waveguide (CPW) tunable transmission lines were evaluated. The differential phase shift increased from 4.4 to 16° at 20 GHz with the sandwich structure (upper BST film thickness, 600 nm, CPW line gap, 5 µm and length, 2500 µm) with an insertion loss of 5.5 dB, when a dc bias voltage from 0 to 30 V was applied. The figure-of-merit improved from the single BST film (1.0°/dB) to the sandwich (2.9°/dB) structure at 20 GHz. Finally, it was confirmed that the sandwich structure is a good candidate for improving the characteristics of microwave tunable devices.

Epitaxial Growth and Ferroelectric Properties of PbTiO_{3} Nanoislands and Thin Films Grown on Single-Crystalline Pt Films

Hironori Fujisawa, Yoshihiro Seioh, Masayoshi Kume, and Masaru Shimizu — 2008-09-19T12:10:00+09:00

Authors: Hironori Fujisawa, Yoshihiro Seioh, Masayoshi Kume, and Masaru Shimizu
Single-crystalline Pt (SC-Pt) films 15–60 nm thick with an atomically flat surface were coherently grown on SrTiO_{3}(100) substrates by rf magnetron sputtering using Ir buffer layers. In the epitaxial growth of PbTiO_{3} films on SC-Pt films by metalorganic chemical vapor deposition, square nanoislands with heights of 3–30 nm and widths of 30–200 nm were grown by self-assembly at the initial growth stage, and subsequently, a continuous film was formed, indicating the Volmer–Weber growth mode. The minimum thickness required to form a continuous PbTiO_{3} film on SC-Pt films was 50 nm, which is much smaller than the 100 nm thickness on partially relaxed Pt films. Piezoresponse force microscopy revealed that piezoelectric constants of PbTiO_{3} nanoislands with heights below 10 nm were distinctly dependent on the height rather than the aspect ratio, suggesting intrinsic size effects of the piezoelectric constant. Continuous PbTiO_{3} films with thicknesses down to 50 nm exhibited saturated hysteresis loops with remanent polarizations of 57–64 µC/cm^{2} and coercive fields of 166–275 kV/cm.

Raman Spectroscopy Study of Oxygen Vacancies in PbTiO_{3} Thin Films Generated Heat-Treated in Hydrogen Atmosphere

2008-09-19T12:10:00+09:00

Authors: Ken Nishida, Minoru Osada, Hironari Takeuchi, Ishimoto Yosiaki, Joe Sakai, Nobuaki Ito, Rikyu Ikariyama, Takafumi Kamo, Takashi Fujisawa, Hiroshi Funakubo, Takashi Katoda, and Takashi Yamamoto
Raman spectroscopy is utilized to study the evaluation of vacancies in PbTiO_{3} thin films subjected to hydrogen atmosphere heat treatment. The B_{1} mode consisted of only oxygen ion vibration was shifted to lower frequency with increasing heat treatment temperature. It was considered that the oxygen ions were lacking from PbTiO_{3}, and that oxygen vacancies were generated. It was found that the frequency of the B_{1} mode is proportional to oxygen ion content. Pb ions were also lacking in the PbTiO_{3} thin films with oxygen ions and the number of oxygen vacancies was larger than that of Pb ions. We suggest that the Raman spectroscopy is a suitable tool for the evaluation of oxygen vacancies in PbTiO_{3} thin films.

Origin of Compressive Residual Stress in Alkoxide Derived PbTiO_{3} Thin Film on Si Wafer

2008-09-19T12:10:00+09:00

Authors: Tomoya Ohno, Babara Mali\uc, Hiroaki Fukazawa, Naoki Wakiya, Hisao Suzuki, Takeshi Matsuda, and Marija Kosec
In this paper, we describe the estimation of residual stress in the alkoxide-derived lead titanate (PTO) thin film on Si substrate by X-ray diffraction (XRD) and Raman analyses. The residual stress that was estimated by XRD and Raman analyses was compressive, and the values obtained by both methods were nearly the same. The residual stress in the PTO thin film increased with decreasing film thickness. We also attempted to calculate the theoretical stress in PTO thin films with random orientation. From the theoretical calculations, the thermal stress that comes from the difference in the thermal expansion coefficient between the Si substrate and the PTO film is calculated to be tensile. On the other hand, the phase transition stress is calculated to be compressive. In addition, this compressive phase transition stress canceled out the tensile thermal stress.

Rapid Crystallization of Sol–Gel-Deposited Lead Zirconate Titanate Thin Films by 2.45 GHz Microwave Irradiation

Zhan Jie Wang, Yuka Otsuka, Ziping Cao, Noboru Yoshikawa, and Hiroyuki Kokawa — 2008-09-19T12:10:00+09:00

Authors: Zhan Jie Wang, Yuka Otsuka, Ziping Cao, Noboru Yoshikawa, and Hiroyuki Kokawa
Pb(Zr_{0.52}Ti_{0.48})O_{3} (PZT) thin films were coated onto Pt/Ti/SiO_{2}/Si substrates by a sol–gel method and then crystallized by 2.45 GHz microwave irradiation in a magnetic field. The crystalline phases and microstructures as well as the electrical properties of the microwave-irradiated PZT films were investigated as a function of the elevated temperature generated by microwave irradiation. The perovskite PZT thin films with good electrical properties could be obtained by microwave irradiation at 650 °C for 60 s. The average values of the remanent polarization and the coercive field of the PZT films were approximately 27 µC/cm^{2} and 95 kV/cm, respectively, whereas the dielectric constant and loss value measured at 1 kHz were approximately 1100 and 0.18, respectively. It is clear that microwave irradiation is effective for obtaining well-crystallized PZT films with good properties in a short process time.

Low-Temperature Crystallization of PbZr_{0.3}Ti_{0.7}O_{3} Film Induced by High-Oxygen-Pressure Processing

2008-09-19T12:10:00+09:00

Authors: Xiaodong Zhang, Xiangjian Meng, Jinglan Sun, Tie Lin, Jianhua Ma, Junhao Chu, and Joonghoe Dho
A 300-nm-thick PbZr_{0.3}Ti_{0.7}O_{3} [PZT(30/70)] film was sputtered onto LaNiO_{3} (LNO)/Si(100) substrates at a substrate temperature of 200 °C and then annealed under an oxygen pressure of 4 MPa at 400 °C. The amorphous phase of the as-sputtered PZT(30/70) film was transformed to a highly (h00)-oriented perovskite phase by high-oxygen-pressure-processing (HOPP). The results of electrical measurements such as of polarization (P) as functions of applied electric field (E) (P–E hysteresis loops), the capacitance as functions of the applied dc electric field (C–E loops), and the dielectric constant (ε_{r}) and dissipation factor (tanδ) suggested that ferroelectric properties of PZT(30/70) films were largely improved by HOPP. We consider that HOPP is compatible with currently existing silicon-based technology, which is characterized by incorporating sputtering and a processing temperature limit of ∼450 °C. The P–E hyteresis loops obtained from a prototype of 128 ×128 uncooled infrared detector arrays prepared by HOPP supported the good ferroelectricity with a high pyroelectric coefficient.

A Ferroelectric Gate Field Effect Transistor with a ZnO/Pb(Zr,Ti)O_{3} Heterostructure Formed on a Silicon Substrate

Hiroyuki Tanaka, Yukihiro Kaneko, and Yoshihisa Kato — 2008-09-19T12:10:00+09:00

Authors: Hiroyuki Tanaka, Yukihiro Kaneko, and Yoshihisa Kato
We have developed a ferroelectric gate field effect transistor (FeFET) with a stacked oxide structure of ZnO/Pb(Zr,Ti)O_{3} (PZT)/SrRuO_{3} (SRO) on a Pt/SiO_{2}-coated silicon substrate. The PZT film which acted as a ferroelectric gate insulator was completely oriented in the (111) direction. The well oriented PZT film was realized by the insertion of the SRO layer, which electrically acted, together with the bottom Pt layer as a bottom gate electrode. In order to realize a sharp heterointerface of ZnO/PZT, we applied chemical–mechanical-polishing (CMP) to the PZT surface giving rise to a minimized surface roughness of less than 0.65 nm (rms). The ZnO film stacked on the smooth PZT surface exhibited a c-axis orientation. Subsequently, the source and drain electrodes of Pt/Ti were formed on the ZnO surface. With a drain-to-source voltage of 0.1 V, the conduction current through the ZnO/PZT heterointerface was characterized. A large on/off current ratio (I_{on}/I_{off}) higher than 10^{5} was obtained between the gate voltage conditions of +10 and -10 V owing to the polarization reversal of the PZT gate. Notably, the on/off ratio was stable for more than 10^{5} s without the application of gate bias.

Microelectromechanical Systems-Based Electrostatic Field Sensor Using Pb(Zr,Ti)O_{3} Thin Films

2008-09-19T12:10:00+09:00

Authors: Takeshi Kobayashi, Syoji Oyama, Masaharu Takahashi, Ryutaro Maeda, and Toshihiro Itoh
We have developed microelectromechanical system (MEMS)-based electrostatic field sensors using Pb(Zr,Ti)O_{3} thin films. Multilayers of Pt/Ti/PZT/Pt/Ti/SiO_{2} deposited on silicon-on-insulator (SOI) wafers have been fabricated into the sensors through MEMS microfabrication technology. The resonant frequency of the fabricated sensors is within 1700–1800 Hz. The developed MEMS-based electrostatic field sensors have shown a good linear response to the voltage of an electrified body, which is comparable to that of commercially available electrostatic field sensors.

In-Plane Lattice Strain Evaluation in Piezoelectric Microcantilever by Two-Dimensional X-ray Diffraction

2008-09-19T12:10:00+09:00

Authors: Hitoshi Morioka, Keisuke Saito, Takeshi Kobayashi, Toshiyuki Kurosawa, and Hiroshi Funakubo
Two-dimensional X-ray diffraction (XRD^{2}) was applied to the in-plane strain evaluation of the piezoelectric microcantilever fabricated from the (001)-/(100)-oriented Pb(Zr_{0.52},Ti_{0.48})O_{3} film deposited on a (001)_{c} LaNiO_{3}/(111) Pt/TiO_{2}/SiO_{2}/Si/SiO_{2}/(001) Si substrate under the applied voltage. In-plane lattice parameters were estimated using XRD^{2} results with two different diffractions originated from PZT, surface normal 002/200 diffractions at χ= 0 and 45° rotated 101/110 diffractions from surface normal (χ= 45°). The out-of-plane and in-plane lattice parameters were linearly increased and decreased by increasing the applied voltage, regardless of the a- and c-axes. A significant 90°-domain rotation from the a-domain to the c-domain was not observed in the microcantilever. The calculated transverse piezoelectric constants (d_{31}) based on the in-plane strain, curvature, and z-displacement indicated similar values of about -140±10 pm/V. This result shows that the in-plane lattice strain mainly contributed to the displacement of the cantilever.

Electrooptic and Piezoelectric Properties of (Pb,La)(Zr,Ti)O_{3} Films with Various Zr/Ti Ratios

2008-09-19T12:10:00+09:00

Authors: Hiromi Shima, Takashi Iijima, Hiroshi Funakubo, Takashi Nakajima, Hiroshi Naganuma, and Soichiro Okamura
A systematic investigation of the electrooptic properties of (Pb,La)(Zr,Ti)O_{3} (PLZT) films was carried out. 700-nm-thick polycrystalline PLZT films with 2 mol % La and various Zr/Ti ratios were formed on Pt/Ti/SiO_{2}/Si substrates, and their reflectance spectra were measured. Zr/Ti ratio significantly affected the surface morphology of the films, and PLZT films with what Ti/(Zr+Ti) ratios ranging from 40 to 70% showed less reflectance light loss that because of their smooth surface. The maximum resonant wavelength shift was attained at a Ti/(Zr+Ti) ratio of 40%. These results suggest that the PLZT film with a Ti/(Zr+Ti) ratio of 40% is optimum for application in optical devices such as a spatial light modulator (SLM). The piezoelectric properties of the PLZT films were also evaluated because their resonant wavelength shift was caused by changes in not only refractive index but also film thickness. The piezoelectric displacement showed a maximum Ti/(Zr+Ti) ratio of 10% and monotonically decreased with increasing Ti/(Zr+Ti) ratio in our PLZT films. The exact Pockels coefficient of the PLZT(2/60/40) film was estimated to be 104 pm/V at 600 nm by subtracting the effect of the change in film thickness from the resonant wavelength shift.

Electro-optic Anisotropy of Epitaxially Grown (Pb,La)(Zr,Ti)O_{3} Films Fabricated by Modified Sol–Gel Process

2008-09-19T12:10:00+09:00

Authors: Masahiro Echizen, Takeshi Fujii, Takashi Nozaka, Takashi Nishida, Hiroaki Takeda, Kiyoshi Uchiyama, and Tadashi Shiosaki
High-quality epitaxially grown (Pb,La)(Zr,Ti)O_{3} (PLZT) films were successfully fabricated on single-crystalline sapphire (012) substrates using a modified sol–gel process. The crystallographic relationship between the PLZT film and the sapphire substrate, and the detailed electro-optic (EO) properties of the films were investigated. Large linear EO coefficients, as large as 510 pm/V, were obtained when an electric field was applied at a 45° angle to the PLZT {110}. In turn, smaller EO coefficients were obtained when an electric field was applied at 0° and 90° angles to the PLZT {110}. A strong EO anisotropy was observed according to the configuration of the input light polarization and the applied electric field.

Effect of Eu/Sr Ratios on Ferroelectric and Fluorescent Properties of Eu-Substituted Strontium Bismuth Tantalate Films

Koji Aizawa and Yusuke Ohtani — 2008-09-19T12:10:00+09:00

Authors: Koji Aizawa and Yusuke Ohtani
The ferroelectric and fluorescent properties of Eu-substituted strontium bismuth tantalate (Eu-SBT) films grown on Pt/Ti/SiO_{2}/Si substrates by spin coating were investigated. The polycrystalline Eu-SBT films with Aurivillius phases were grown at Eu/Sr ratios between 0 and 0.25. Moreover, the lattice constants along the a- and c-axes at Eu/Sr=0.25 in comparison with Eu/Sr=0 decreased by approximately 0.36 and 0.19%, respectively. The remnant polarization values of the Eu-SBT films with Eu/Sr ratios of 0 and 0.25 were approximately 6.6 and 5.8 µC/cm^{2}, respectively. The 80%-fatigue endurance of a Eu-SBT film with Eu/Sr=0.25 was approximately 3.1×10^{9} cycles when a 10 kHz triangular wave with an amplitude of 8 V (approximately 530 kV/cm electric field) was used. The photoluminescence intensity of the Eu-SBT films was increased by Eu doping with negligible change of the remnant polarization. Emission peaks at approximately 600 nm in wavelength, which were associated with the ^{5}D_{0}–^{7}F transitions of Eu^{3+}, were observed in the Eu-SBT films.

Effects of Electron-Cyclotron-Resonance Oxygen Plasma Irradiation on Properties of Insulator/Ge-Semiconductor Interfaces Prior to Germanium Nitride Formation

2008-09-19T12:10:00+09:00

Authors: Yohei Otani, Yukio Fukuda, Tetsuya Sato, Kiyokazu Nakagawa, Hiroshi Toyota, and Toshiro Ono
Electron-cyclotron-resonance (ECR) oxygen (O_{2}) plasma was irradiated onto the surface of germanium (Ge) substrates prior to germanium nitride (GeN_{x}) formation. Germanium metal–insulator–semiconductor (Ge-MIS) structures with a 5-nm-thick silicon nitride/2-nm-thick GeN_{x} gate insulator stack fabricated by ECR plasma nitridation and sputtering deposition without substrate heating were electrically and physically characterized. Although ECR O_{2} plasma irradiation onto the surface of Ge substrates caused no significant difference in the chemical state of GeN_{x}/Ge interfaces in X-ray photoemission spectroscopic measurement, irradiation for an appropriate period improved the state of GeN_{x}/Ge interfaces and the electrical properties of Ge-MIS.

Langmuir–Blodgett Fabrication of Nanosheet-Based Dielectric Films without an Interfacial Dead Layer

2008-09-19T12:10:00+09:00

Authors: Minoru Osada, Kosho Akatsuka, Yasuo Ebina, Yoshinori Kotani, Kanta Ono, Hiroshi Funakubo, Shigenori Ueda, Keisuke Kobayashi, Kazunori Takada, and Takayoshi Sasaki
Langmuir–Blodgett (LB) deposition was employed to fabricate high-κ dielectric nanofilms of titania nanosheets. The LB-based layer-by-layer approach using an atomically flat SrRuO_{3} substrate is effective for the fabrication of atomically uniform and highly dense nanofilms. These films exhibited both high dielectric constant (κ∼123) and low leakage current density (J< 10^{-7} A cm^{-2}) for thicknesses down to 5 nm, while eliminating the size-effect problems encountered in current high-κ films. From analyses of interfacial structures by transmission electron microscopy and hard X-ray photoelectron spectroscopy, we have clarified that the films are composed of a well-ordered lamellar structure without an interfacial dead layer. According to first-principles calculations, a highly polarizable nature of titania nanosheets can bring improved dielectric properties, yielding high-κ values even in an ultrathin geometry (<10 nm).

Effects of Flat HfO_{2} Films Derived from Diethanolamine Solution on Structure and Properties of Metal/Ferroelectrics/Insulator/Semiconductor

Kazuyuki Suzuki, Kiyotaka Tanaka, and Kazumi Kato — 2008-09-19T12:10:00+09:00

Authors: Kazuyuki Suzuki, Kiyotaka Tanaka, and Kazumi Kato
HfO_{2} films were prepared using precursor solutions with and without diethanolamine. The microstructure of HfO_{2} films changed with the presence of diethanolamine. This result is thought to be due to the difference in the progress of organic decomposition and the behavior of nucleation and grain growth. The microstructure of HfO_{2} films affected the crystallization and microstructure of Y_{0.5}Yb_{0.5}MnO_{3} films on these HfO_{2} films. The flatness of HfO_{2} and Y_{0.5}Yb_{0.5}MnO_{3} films was improved by the modification of HfO_{2} precursor solutions with diethanolamine.

Development of Pt/MgO(100) Buffer Layers for Orientation Control of Perovskite Oxide Thin Films

2008-09-19T12:10:00+09:00

Authors: Tatsuro Matsumoto, Kazuhiro Tamai, Yuuji Murashima, Kazuki Komaki, and Shigeki Nakagawa
(100)-oriented MgO thin films can be effectively grown at a substrate temperature of room temperature (RT) on Fe seed layers by the facing-targets sputtering (FTS) method. Pt(100) orientation was observed when the Pt layer was deposited on MgO(100)/Fe buffer layers at a substrate temperature above 350 °C. Pt thin films can be grown effectively with (100) orientation and with smaller strain when they are prepared at a substrate temperature above 500 °C. Also, Ba_{1-x}Sr_{x}TiO_{3} (BST) thin films with (100) preferential orientation can be grown on Pt(100)/MgO(100)/Fe buffer layers when Pt and BST films are deposited at a substrate temperature of 500 °C. Pt(100)/MgO(100)/Fe buffer layers are very effective for attaining BST(100) orientation.

Effect of Mn Substitution for Multiferroic BiFeO_{3} Probed by High-Resolution Soft-X-ray Spectroscopy

2008-09-19T12:10:00+09:00

Authors: Tohru Higuchi, Takeshi Hattori, Wataru Sakamoto, Naoyuki Itoh, Tetsuo Shimura, Toshinobu Yogo, Peng Yao, Yi-Sheng Liu, Per-Anders Glans, Chinglin Chang, Ziyu Wu, and Jinghua Guo
The electronic structures of BiFeO_{3} (BF) and Mn-doped BiFeO_{3} [BF(Mn)] have been studied by X-ray absorption spectroscopy (XAS) and soft-X-ray emission spectroscopy (SXES). BF and BF(Mn) have a mixed valence state of Fe^{2+} and Fe^{3+}. Their valence band is mainly composed of the O 2p state hybridized with the majority-spin t_{2g} and e_{g} orbitals of Fe 3d state. The conduction band is composed of the minority-spin t_{2g} and e_{g} orbitals of Fe 3d. The band gaps of BF and BF(Mn) are estimated to be 1.3 eV and 2.7 eV, respectively. The increase in band gap with Mn substitution contributes to a change in the bandwidth of the valence band.

Annealing Temperature Dependences of Ferroelectric and Magnetic Properties in Polycrystalline Co-Substituted BiFeO_{3} Films

2008-09-19T12:10:00+09:00

Authors: Hiroshi Naganuma, Jun Miura, Mitsumasa Nakajima, Hiromi Shima, Soichiro Okamura, Shintaro Yasui, Hiroshi Funakubo, Ken Nishida, Takashi Iijima, Masaki Azuma, Yasuo Ando, Kenji Kamishima, Koichi Kakizaki, and Nobuyuki Hiratsuka
Multiferroic Co-substituted BiFeO_{3} films were fabricated by chemical solution deposition method followed by post deposition annealing at various temperatures. The substitution of cobalt of B-sites for iron in BiFeO_{3} was promoted at relatively high temperatures. The B-site substitution by cobalt promoted increases in saturation magnetization and spontaneous magnetization. By substitution, leakage current density was suppressed in a high-electric-field region, and ferroelectric hysteresis (P–E) loops became measurable even at room temperature. The optimal annealing temperature for the coexistence of a high remanent polarization and a high remanent magnetization was 923 K having a high B-site substitution ratio of cobalt.

Rhombohedral–Tetragonal Phase Boundary with High Curie Temperature in (1-x)BiCoO_{3}–xBiFeO_{3} Solid Solution

2008-09-19T12:10:00+09:00

Authors: Masaki Azuma, Seiji Niitaka, Naoaki Hayashi, Kengo Oka, Mikio Takano, Hiroshi Funakubo, and Yuichi Shimakawa
The crystal structure change of the solid solution BiCo_{1-x}Fe_{x}O_{3} was investigated in order to determine the phase boundary between tetragonal BiCoO_{3} and rhombohedral BiFeO_{3}. It was found that BiCo_{1-x}Fe_{x}O_{3} with x = 0 to 0.6 had tetragonal BiCoO_{3} structures, while those with x = 0.8 to 1 had rhombohedral BiFeO_{3} structures at room temperature. The monoclinic √2a ×√2a ×a phase was found for the x = 0.7 sample. The tetragonal-to-cubic phase transition was first observed at around 700–850 °C in Bi-based perovskite for the x = 0.8 sample.

Crystal Structure and Electrical Properties of {100}-Oriented Epitaxial BiCoO_{3}–BiFeO_{3} Films Grown by Metalorganic Chemical Vapor Deposition

2008-09-19T12:10:00+09:00

Authors: Shintaro Yasui, Hiroshi Naganuma, Soichiro Okamura, Ken Nishida, Takashi Yamamoto, Takashi Iijima, Masaki Azuma, Hitoshi Morioka, Keisuke Saito, Mutsuo Ishikawa, Tomoaki Yamada, and Hiroshi Funakubo
xBiCoO_{3}–(1 - x)BiFeO_{3} (x = 0–0.22) films of 400 nm thickness were grown on (100)_{c} SrRuO_{3}∥(100) SrTiO_{3} substrates by metalorganic chemical vapor deposition. The changes in the crystal structure and electrical properties of the films with x were investigated. The constituent phase changed from rhombohedral to a mixture of rhombohedral and tetragonal, and to tetragonal with increasing x, but the x for this transition is different from that of 200-nm-thick films grown on (100) SrTiO_{3} substrates. The x of the morphotropic phase boundary that consisted of a mixture of tetragonal and rhombohedral symmetries depended on the film thickness. The remanant polarization continuously decreased with increasing x, in good agreement with the results obtained with the {100}-oriented Pb(Zr,Ti)O_{3} epitaxial films owing to the decrease in the crystal anisotropy of the films.

Composition Dependence in BiFeO_{3} Film Capacitor with Suppressed Leakage Current by Nd and Mn Cosubstitution and Their Ferroelectric Properties

2008-09-19T12:10:00+09:00

Authors: Takeshi Kawae, Hisashi Tsuda, Hiroshi Naganuma, Satoru Yamada, Minoru Kumeda, Soichiro Okamura, and Akiharu Morimoto
(Nd,Mn)-cosubstituted BiFeO_{3} (BFO) films with various Nd and Mn compositions were fabricated on a Pt/SrTiO_{3}(100) substrate by pulsed laser deposition. X-ray diffraction patterns and atomic force microscopy images indicated that the suppression of impurity phases and a smooth surface morphology were realized by Nd substitution in the BFO films. Furthermore, by combining with Nd substitution, a small amount of Mn substitution in BFO films is effective for reducing the leakage current density by three orders of magnitude compared with that of a BFO film capacitor. The polarization vs electric field (P–E) curves showed a strong dependence of measurement frequency in the range of 0.1–2 kHz, and well-saturated P–E hysteresis loops were observed at 20 kHz at room temperature. The remanent polarization and coercive field at a maximum electric field of 1.9 MV/cm were approximately 70 µC/cm^{2} and 0.32 MV/cm, respectively.

Local Structure of BiFeO_{3}–BaTiO_{3} Mixture

Yasuhiro Yoneda, Kenji Yoshii, Shinji Kohara, Shuji Kitagawa, and Shigeo Mori — 2008-09-19T12:10:00+09:00

Authors: Yasuhiro Yoneda, Kenji Yoshii, Shinji Kohara, Shuji Kitagawa, and Shigeo Mori
Local structure analysis of (1-x)BiFeO_{3}–xBaTiO_{3} mixture was carried out by a synchrotron radiation X-ray pair-distribution function (PDF) method. The PDF peak is resolved as a doublet owing to the presence of two phases with distinct local structures. The randomness of the off-center displacement of Bi atoms was different in these two phases, one was an average structure and the other a disordered rhombohedral structure. The volume fraction of each phase changed with BaTiO_{3} composition.

Effect of Oxygen Vacancies on Charge Ordered Structure in YFe_{2}O_{4-δ}

2008-09-19T12:10:00+09:00

Authors: Shigeo Mori, Satoshi Shinohara, Yoji Matsuo, Yoichi Horibe, Kenji Yoshii, and Naoshi Ikeda
The effect of oxygen vacancies on the charge ordered structure at room temperature (RT) in YFe_{2}O_{4-δ} was investigated by transmission electron microscopy (TEM) and it was found that the charge ordered structure is sensitive to the amount of oxygen vacancies. Real-space images of the three-dimensional charge ordered structure revealed that the average size of charge ordered domains can be estimated to be 20 nm. These nanosized charge ordered domains are responsible for the dielectric properties of YFe_{2}O_{4-δ}. The charge ordering processes were also examined by in-situ TEM.

Magnetic and Dielectric Properties of HoFe_{2}O_{4} and R_{1-x}R'_{x}Fe_{2}O_{4} (R, R': Rare Earths)

2008-09-19T12:10:00+09:00

Authors: Kenji Yoshii, Yasuhiro Yoneda, Daisuke Maeda, Yusuke Yokota, Takamasa Michiuchi, Takuma Komatsu, Naoshi Ikeda, Yoji Matsuo, and Shigeo Mori
Rare-earth iron oxides of the form RFe_{2}O_{4} (R = Y, Ho–Lu) show a new mechanism of ferroelectricity owing to the charge ordering of Fe ions below ∼330 K. To determine the physical properties of this system, the magnetic and dielectric properties of HoFe_{2}O_{4} and R_{1-x}R'_{x}Fe_{2}O_{4} were investigated (R, R': rare earths). All the materials showed dielectric constants of ∼1000–10000, as reported for some other RFe_{2}O_{4} oxides. For HoFe_{2}O_{4}, magnetic ordering occurred at a temperature lower than those of RFe_{2}O_{4} reported thus far. On the other hand, the dielectric measurements of this material suggested the development of a correlation between polar regions at higher temperatures, which was also observed for the Sc-substituted system Lu_{1-x}Sc_{x}Fe_{2}O_{4}. These results encourage detailed investigations of these materials from the viewpoints of both fundamental and applied sciences, and suggest the existence of other new properties of RFe_{2}O_{4}.

Modification of Ferroelectric Properties of BaTiO_{3}–CoFe_{2}O_{4} Multiferroic Composite Thin Film by Application of Magnetic Field

2008-09-19T12:10:00+09:00

Authors: Shigeki Sawamura, Naoki Wakiya, Naonori Sakamoto, Kazuo Shinozaki, and Hisao Suzuki
We prepared BaTiO_{3}–CoFe_{2}O_{4} composite thin film on (La_{0.5}Sr_{0.5})CoO_{3}/CeO_{2}/YSZ/Si(100) substrate by pulsed laser deposition. Simultaneous epitaxial growths of BaTiO_{3} and CoFe_{2}O_{4} were achieved. Reciprocal space map measurement revealed that the lattice parameters of BaTiO_{3} parallel and perpendicular to the substrate are 0.4239 and 0.4060 nm, respectively. The fact that both lattice parameters are larger than those of the bulk (a = 0.3994, c = 0.4038 nm) suggests that the BaTiO_{3} film contains a considerable amount of oxygen vacancies, and a relatively large tensile stress is observed along the direction parallel to the substrate. These results indicate that the BaTiO_{3} film has (h00) orientation; however, we consider that the small amount of (00l) orientation component is also included although the (00l) orientation component is not clearly detected by X-ray diffraction. The magnetization–magnetic field (M–H) hysteresis measurement revealed that the film had a high perpendicular coercivity of 7.0 kOe. In addition, a distinct perpendicular magnetic anisotropy was observed. The distribution of magnetic domains was observed by magnetic force microscopy. Polarization–electric field (P–E) hysteresis measurement revealed that the BaTiO_{3}–CoFe_{2}O_{4} composite film had weak ferroelectricity with considerable leakage current. It was also found that the shape of the P–E curve was changed by the application of a lateral magnetic field of 0.2 T. The change would have been caused by the following two possibilities: (1) magnetostriction of CoFe_{2}O_{4} and (2) magnetic resistivity of CoFe_{2}O_{4} or (La_{0.5}Sr_{0.5})CoO_{3}.

Domain Size Effect on Dielectric Properties of Barium Titanate Ceramics

2008-09-19T12:10:00+09:00

Authors: Takuya Hoshina, Kayo Takizawa, Jianyong Li, Takeshi Kasama, Hirofumi Kakemoto, and Takaaki Tsurumi
Barium titanate (BaTiO_{3}) ceramics with various grain sizes were prepared by a conventional sintering method and a two-step sintering method. The permittivity of the ceramics increased with decreasing the grain size down to 1.1 µm on average. The BaTiO_{3} ceramics with an average grain size of 1.1 µm had a high permittivity of 7,700. The transmission electron microscopy (TEM) observation revealed that the 90° domain density increased with decreasing the grain size. The domain size of the ceramics with the highest permittivity of 7,700 was approximately 100 nm. From an ultra wide range dielectric spectroscopy, it was found that the high domain density enhanced the orientational polarizability due to the domain-wall vibration and the ionic polarizability due to the lattice vibration. It was clarified that the increase of the permittivity with decreasing the grain size was due to the domain size effect.

Preparation of Highly Dispersed Barium Titanate Nanoparticles from Barium Titanyl Oxalate Nanoparticles and Their Dielectric Properties

Satoshi Wada, Shuhei Kondo, Chikako Moriyoshi, and Yoshihiro Kuroiwa — 2008-09-19T12:10:00+09:00

Authors: Satoshi Wada, Shuhei Kondo, Chikako Moriyoshi, and Yoshihiro Kuroiwa
Barium titanate (BaTiO_{3}) crystallites with various particle sizes from 10 to 300 nm were prepared by the two-step thermal decomposition method of barium titanyl oxalate nanoparticles with a particle size of 30 nm under vacuum to prepare defect-free BaTiO_{3} nanoparticles with a thin surface cubic layer. Various characterizations revealed that the obtained particles were defect-free, dense BaTiO_{3} nanoparticles. Scanning electron microscopy (SEM) revealed that BaTiO_{3} nanoparticles prepared from oxalate nanoparticles were nonaggregated and highly dispersed. Moreover, the mesoscopic particle structure of BaTiO_{3} nanoparticles was investigated using a synchrotron X-ray diffraction (XRD) analysis and a two-layer model, i.e., the (1) surface cubic layer and (2) bulk tetragonal layer, and it was confirmed that the thickness of the surface cubic layer was always below 5 nm regardless of particle size. Finally, the dielectric property of BaTiO_{3} nanoparticles was measured by powder dielectric measurement at 20.00 °C and 20 MHz, and a high dielectric constant of around 30,000 was obtained for the BaTiO_{3} nanoparticles with sizes between 60 and 85 nm.

Synthesis and Dielectric-Magnetic Properties of Rare-Earth (La, Nd, Sm)-Modified Bi_{4}Ti_{3}O_{12}

2008-09-19T12:10:00+09:00

Authors: Tatsuhiro Shigyo, Hajime Kiyono, Junya Nakano, Hidenobu Itoh, and Junichi Takahashi
Rare-earth (RE = La, Nd, Sm)-substitution into BiT (Bi_{4-X}RE_{X}Ti_{3}O_{12}) was conducted in a composition range of 0 ≤X ≤3.0. BiT powders, into which fixed amounts of RE cations were incorporated, were directly synthesized by low-temperature calcination of coprecipitated precursors. Complete substitution with RE was achieved for samples up to X = 2.5 at 1100 °C. Dielectric permittivity (ε_{r})–temperature curves of the La-2.0, Nd-2.0, and Sm-2.0 ceramics showed ε_{r} maxima in a frequency-dependent manner. The ε_{r} maxima were located at around 540–560 °C (at 1 kHz), which corresponded to the transition from the ferroelectric to paraelectric phase. Increasing Nd-substitution from X = 2.0 to 2.5 resulted in a much suppressed ε_{r} maximum at 200–300 °C, which may be due to substantial reduction in the structural distortion giving rise to ferroelectricity of the BiT-based phase. The appearance and enhancement of magnetization was found for the Nd- and Sm-substituted BiT samples. They revealed specified magnetization–magnetic field curves with a small hysteresis loop, suggesting the presence of a weak canted antiferromagnetic interaction.

High-Performance Bi_{0.5}Na_{0.5}TiO_{3} Single Crystals Grown by High-Oxygen-Pressure Flux Method

Katsuya Yamamoto, Muneyasu Suzuki, Yuji Noguchi, and Masaru Miyayama — 2008-09-19T12:10:00+09:00

Authors: Katsuya Yamamoto, Muneyasu Suzuki, Yuji Noguchi, and Masaru Miyayama
High-P_{O_2} (oxygen pressure) crystal growth is developed for Bi_{0.5}Na_{0.5}TiO_{3} single crystals based on defect chemistry at high temperatures. Thermogravimetric analysis shows that the vacancy formations of Bi and O at high temperatures are controlled by the surface reaction (oxygen desorption), which is suppressed at a higher P_{O_2}. Bi_{0.5}Na_{0.5}TiO_{3} crystals grown at a P_{O_2} of 1 MPa exhibit a saturated remanent polarization of 44 µC/cm^{2} along [110]_{cubic}, suggesting a spontaneous polarization of 54 µC/cm^{2} along [111]_{cubic} (polar direction) of rhombohedral Bi_{0.5}Na_{0.5}TiO_{3}. High-P_{O_2} heat treatments are proposed to be effective for fabricating high-quality and high-performance ferroelectric/piezoelectric devices using Bi-based ferroelectric oxides.

Preparation of Inkjet-Printed NiO Films for Ba(Ti,Zr)O_{3}-Based Ceramics and Application to Multilayer Ceramics with Ni Electrodes

Yuichi Sakai, Tomoaki Futakuchi, and Masatoshi Adachi — 2008-09-19T12:10:00+09:00

Authors: Yuichi Sakai, Tomoaki Futakuchi, and Masatoshi Adachi
The possibility of fabricating a lead-free multilayer ceramic (MLC) actuator with Ni inner electrodes prepared by inkjet printing has been investigated. Inkjet ink containing NiO powder was prepared. NiO films were prepared on [(BaO)_{1.00}(CaO)_{0.01}](Ti_{0.95}Zr_{0.05})O_{2} green sheets by the inkjet method and co-fired in a reducing atmosphere. After co-firing, the NiO films were reduced to metal Ni films, which acted as electrodes. The remanent polarization P_{r} and coercive field E_{c} of the ceramics were 2.5 µC/cm^{2} and 3.0 kV/cm, respectively. The Curie temperature, orthorhombic–tetragonal transition temperature, and rhombohedral–orthorhombic transition temperature were 110, 45, and 0 °C, respectively. The [(BaO)_{1.00}(CaO)_{0.01}](Ti_{0.95}Zr_{0.05})O_{2} MLCs with Ni inner electrodes were prepared using NiO ink. The diffusion and reaction of Ni to ceramic layers were not observed. The displacement of the MLCs with seven active layers was approximately 0.17 µm when the electric field was 20 kV/cm. It is expected that inkjet printing using NiO ink will be applicable to the fabrication of lead-free MLC actuators with Ni inner electrodes.

Characteristic Pressure Dependence of Spontaneous Polarization in Ferroelectric Liquid Crystal

Hiroyuki Uehara — 2008-09-19T12:10:00+09:00

Authors: Hiroyuki Uehara
The spontaneous polarization and rotational viscosity of the c-director of the ferroelectric liquid crystal 4'-octyloxy-biphenyl-4-carboxylic acid 4-(1-methyl-heptyloxy)-phenyl ester at various pressures were investigated. Spontaneous polarization as a function of T-T_{CA}( p) decreased markedly when pressure was changed from 0.1 to 20 MPa and was independent of pressure as pressure was further increased. Rotational viscosity decreased when pressure was applied. These results suggest that the conformation of liquid crystal molecules changes at pressures below 20 MPa.

Helical Structure in Antiferroelectric Liquid Crystals

Hirokazu Furue, Hiroe Kuramochi, and Daisaku Kakinuma — 2008-09-19T12:10:00+09:00

Authors: Hirokazu Furue, Hiroe Kuramochi, and Daisaku Kakinuma
The helical structure in an antiferroelectric liquid crystal (AFLC) phase may show a complicated temperature dependence such as the change in the helical handedness. However, the mechanism of the helical arrangement of molecules has not been clarified. In this study, we investigated the temperature dependence of the helical structure using several types of AFLC material and the effect of the optical purity on the helical structure in terms of optical rotatory power (ORP) and circular dichroism (CD). Results show that the increase in the helical pitch, which originates from a decline of the optical purity, is not due to the decrease in the macroscopic twisting power but the microscopic coexistence of both the helical handedness. Furthermore, it is clear that the change in the helical handedness is a premonitory phenomenon of the phase transition from the antiferroelectric smectic C (SmC_{A}^{*}) to the lower temperature phase such as the crystal phase. On the other hand, it is confirmed that the change in the helical handedness is not intrinsic to all AFLC media.

Electrically Controlled Piezoelectric Motion of Piezoelectric Chiral Polymeric Fibers

2008-09-19T12:10:00+09:00

Authors: Masahiro Honda, Michiya Sawano, Yasuhiro Uenaka, Katsunori Morii, Ken Yamamoto, and Yoshiro Tajitsu
The electrically controlled piezoelectric motion of a fiber of poly(l-lactic acid) (PLLA), a type of chiral polymer, is investigated. Laser light was propagated into the PLLA fiber, and when the controlling electric field was applied to the fiber, the direction of the outgoing beam from the fiber changed owing to its piezoelectric motion. The change in direction was recorded using two charge coupled device (CCD) video cameras: one faces the tip of the PLLA fiber and the other is placed above the tip of the fiber. First, it was realized that the outgoing beam moved in a zigzag manner when we applied the ac voltage with high harmonic waves to the PLLA fiber. Furthermore, when a component parallel to the PLLA fiber axis of the applied electric field was generated, the trajectory of the outgoing beam changed from a straight line to an ellipse.

Preparation and Properties of BaTiO_{3} Ceramics by Spark Plasma Sintering

Hiroshi Maiwa — 2008-09-19T12:10:00+09:00

Authors: Hiroshi Maiwa
BaTiO_{3} (BT) ceramics are prepared by spark plasma sintering (SPS) and conventional sintering. In conventional sintering, the density and grain size of the ceramics increase with sintering temperature. In SPS, ceramics with more than 97% relative densities can be obtained by sintering at 900 °C for 5 min in air atmosphere. Compared with conventional sintering, SPS suppresses grain growth in ceramics. The average grain size of the BT ceramics obtained by SPS and subsequent annealing at 1000 °C for 12 h is less than 1 µm. The ceramics exhibit a high relative dielectric constant of 6020. The field-induced displacement of the BT ceramics is larger than that of the ceramics sintered conventionally. The dynamic strain/field at 15 kV/cm was 540 pm/V.

Effects of Pressure on Piezoelectric and Dielectric Responses of Relaxor Ferroelectric Solid Solution Pb(Mg_{1/3}Nb_{2/3})O_{3}–PbTiO_{3} Binary System Ceramics near a Morphotropic Phase Boundary Composition

2008-09-19T12:10:00+09:00

Authors: Naohiko Yasuda, Koichi Ozawa, Md. M. Rahaman, Hidehiro Ohwa, Yohachi Yamashita, Makoto Iwata, and Yoshihiro Ishibashi
The piezoelectric and dielectric properties of Pb(Mg_{1/3}Nb_{2/3})O_{3}–PbTiO_{3} (PMNT) ceramics with compositions near a morphotropic phase boundary (MPB) were investigated under pressures p up to 700 MPa at 25 °C. The resonance and antiresonance frequency characteristics of impedance and phase in the k_{31} mode for PMNT (67/33) and (69/31) ceramics were observed under various pressures. The effect of pressure on their responses were clearly observed. The electromechanical coupling coefficient k_{31} in the k_{31} mode increases and the electromechanical quality factor Q decreases with increasing p at pressures lower than 100 MPa. The decrease in Q with p is due to the scattering of ultrasonic waves from the domain boundary. The relative permittivity ε_{r} increases with increasing p. Such increases in both k and ε_{r} with p seem to be related to the increase in topographical domain-wall density associated with monoclinic distortions. At pressures higher than 100 MPa, their electromechanical suppression in PMNT ceramics occurs at each pressure, corresponding to the electromechanical coupling coefficient k. ε_{r} increases with pressure-induced electromechanical suppression. The change in ε_{r} with such suppression corresponds to k. Such a phenomenon seems to be due to the increase in piezoelectric load based on the increase in complex domain wall density coming from the increase in free energy with pressure.

Giant Transverse-Mode Electromechanical Coupling Factor and Piezoelectric Strain in Relaxor Single-Crystal Plates Evaluated Using P–E Hysteresis Loop

Toshio Ogawa — 2008-09-19T12:10:00+09:00

Authors: Toshio Ogawa
The relationships between the giant piezoelectricity of transverse-mode electromechanical coupling factor k_{31} and longitudinal-mode electromechanical coupling factor k_{33} were studied in the cases of Pb[(Zn_{1/3}Nb_{2/3})_{0.91}Ti_{0.09}]O_{3} (PZNT91/09) with (100) plane and (1 - x)Pb(Mg_{1/3}Nb_{2/3})O_{3}–xPbTiO_{3} [PMNT(1 - x)/x] (x = 0.251–0.301) with (110) plane. From the P–E hysteresis loops and the electric field (E) vs strain measurement, a triple hysteresis loop was observed in PZNT91/09, and triple hysteresis and asymmetric hysteresis loops were obtained in x = 0.273–0.293 and x = 0.251–0.262 in PMNT(1 - x)/x, while the giant k_{31} was realized in the relaxor single crystals. Furthermore, the E required to observe the triple and asymmetric loops corresponded to the E of a break in the line for E vs strain. It was considered that the E was a coercive field to generate the DC-field-induced phase transition with giant k_{31}.

Piezoelectric Properties of (Bi_{1/2}Na_{1/2})TiO_{3}-Based Solid Solution for Lead-Free High-Power Applications

Yuji Hiruma, Tomomi Watanabe, Hajime Nagata, and Tadashi Takenaka — 2008-09-19T12:10:00+09:00

Authors: Yuji Hiruma, Tomomi Watanabe, Hajime Nagata, and Tadashi Takenaka
Lead-free piezoelectric ceramics based on x(Bi_{1/2}Na_{1/2})TiO_{3}–y(Bi_{1/2}Li_{1/2})TiO_{3}–z(Bi_{1/2}K_{1/2})TiO_{3} [x + y + z = 1] (abbreviated as BNLKT100y-100z) were prepared by conventional ceramic fabrication process. In this study, we clarified that the mechanical quality factor Q_{m} of the rhombohedral side of the MPB composition is rather superior to that of the tetragonal side, although the piezoelectric constant d_{33} of the rhombohedral side is lower than that of the tetragonal side and MPB composition. As a second work, the effects of Mn doping on the variations in T_{d} and piezoelectric properties including high-power characteristics were investigated using BNLKT4-8, which is a rhombohedral composition. The Q_{m} of w wt % MnCO_{3}-doped BNLKT4-8 (abbreviated as BNLKT4-8Mnw) markedly increased with increasing Mn concentration w, while T_{d}, coupling factor k_{33}, and d_{33} slightly decreased. The high-power characteristics of BNLKT4-8Mn0.6 were superior to those of hard PZT at a vibration velocity v_{0–p} > 0.6 m/s. Therefore, a Mn-doped BNT-based solid solution with rhombohedral symmetry is a promising candidate for lead-free high-power applications.

Fabrication of High-Density (Bi,La)(Zn,Mg,Ti)O_{3}–PbTiO_{3} Solid Solutions with Ferroelectric and Piezoelectric Functionalities by Microstructural Control

2008-09-19T12:10:00+09:00

Authors: Masafumi Kobune, Wataru Adachi, Kazuya Kitada, Atsushi Mineshige, Tetsuo Yazawa, Hideshi Yamaguchi, and Koichiro Honda
The Bi(Zn_{0.5}Ti_{0.5})O_{3}–PbTiO_{3} solid solution was modified by the replacement of A- and B-site cations in the perovskite crystal with lanthanum and magnesium so as to realize ferroelectric and piezoelectric functionalities. This substitution reduces the covalency and increases the ionic bonding in the crystal. The tetragonal perovskite solid solution with composition 0.33(Bi_{0.7}La_{0.3})(Zn_{0.15}Mg_{0.35}Ti_{0.5})O_{3}·0.67PbTiO_{3} was demonstrated to exhibit ferroelectric and piezoelectric functionalities with high Curie temperature (T_{c} = 300 °C) and parameters of relative permittivity (ε_{33}^{T}/ε_{0} = 410), remanent polarization (P_{r} = 30 µC/cm^{2}), coercive field (E_{c} = 47 kV/cm), piezoelectric coefficient (d_{33} = 94 pC/N), and tolerance factor (t = 0.993). This material is thus suitable for use as a high-temperature piezoelectric with performance comparable to that of Pb(Zr,Ti)O_{3} (PZT).

Synthesis of KNbO_{3} Piezoelectric Ceramics Using Citrate Precursors

Ken-ichi Kakimoto, Takeshi Ito, and Hitoshi Ohsato — 2008-09-19T12:10:00+09:00

Authors: Ken-ichi Kakimoto, Takeshi Ito, and Hitoshi Ohsato
An aqueous-based citrate precursor route has been adopted for the synthesis of KNbO_{3} nanopowders. The required amount of KNO_{3} or C_{6}H_{5}O_{7}K_{3}·H_{2}O solution was mixed with citric Nb solution to form white precipitates, followed by heat treatment at 800 °C to produce KNbO_{3} nanopowders with an average particle size of 250–300 nm. The as-received nanopowder showed a well-sinterable property without using any additives, and the obtained KNbO_{3} ceramics showed saturated ferroelectric hysteresis loops of P_{r} = 22.9 µC/cm^{2} and E_{c} = 7.8 kV/cm at 1 Hz. The excellent piezoelectric properties of k_{p} = 0.35, Q_{m} = 131, k_{31} = 0.23, d_{31} = -31 pC/N, and d_{33} = 110 pC/N were obtained for KNbO_{3} ceramics derived from KNO_{3} solution, whereas k_{p} = 0.29, Q_{m} = 96, k_{31} = 0.20, d_{31} = -45 pC/N, and d_{33} = 115 pC/N were obtained for KNbO_{3} ceramics derived from C_{6}H_{5}O_{7}K_{3}·H_{2}O solution.

Synthesis of Nondoped Potassium Niobate Ceramics by Ultrasonic Assisted Hydrothermal Method

2008-09-19T12:10:00+09:00

Authors: Mutsuo Ishikawa, Yoichi Kadota, Norihito Takiguchi, Hiroshi Hosaka, and Takeshi Morita
Non doped potassium niobate (KNbO_{3}) crystal powders were synthesized by ultrasonic-assisted hydrothermal method for use in lead-free piezoelectric ceramics. By using the ultrasonic assist technique, the yield constant of the KNbO_{3} crystal powders became 96% with 3 h of reaction time. It was 4 times faster than that of the previous non ultrasonic assist hydrothermal method for the KNbO_{3} crystal powders. This result indicated that the high-intensity ultrasound radiation was effective for overcoming the serious problem of slow hydrothermal reaction. The reaction temperature was 190 °C, which was 20 °C lower than that of previous hydrothermal method. After sintering of hydrothermal KNbO_{3} powders at 1030 °C for 1 h, the obtained ceramics pellet was characterized by admittance measurement, and the piezoelectric performance was examined. From the admittance measurements corresponding to the radial and thickness vibration modes, the coupling factors k_{r} and k_{t} and the piezoelectric constants d_{31} and d_{33} were determined to be 0.17 and 0.28, and -31 and 51 pm/V, respectively.

Preparation of Barium Titanate–Potassium Niobate Solid Solution System Ceramics and Their Piezoelectric Properties

2008-09-19T12:10:00+09:00

Authors: Satoshi Wada, Momoyo Nitta, Nobuhiro Kumada, Daisuke Tanaka, Masahito Furukawa, Satoshi Ohno, Chikako Moriyoshi, and Yoshihiro Kuroiwa
Barium titanate (BaTiO_{3}, BT)–potassium niobate (KNbO_{3}, KN) solid solution system ceramics were prepared by normal sintering, and their piezoelectric properties were measured. The phase diagram of the BT–KN system was investigated by dielectric measurement and X-ray diffraction (XRD). The Curie temperature (T_{C}) was almost constant at approximately 130 and 430 °C for ceramics with KN contents below and above 50 mol %, respectively. At room temperature, two phases, ferroelectric tetragonal and ferroelectric orthorhombic, coexisted in the composition range from 0.7BT–0.3KN to 0.1BT–0.9KN. This system was found to be a limited solid solution system that involves BT- and KN-rich phases. Their piezoelectric properties were investigated on the basis of the electric-field dependence of strain measurements. For ceramics with KN contents below 30 mol %, the apparent piezoelectric constant (d_{33}) decreased approximately with increasing KN content, whereas above 30 mol %, the apparent d_{33} increased as a function of KN content.

Hydrothermal Synthesis of (K,Na)NbO_{3} Particles

Fan Zhang, Lu Han, Shan Bai, Tiedong Sun, Tomoaki Karaki, and Masatoshi Adachi — 2008-09-19T12:10:00+09:00

Authors: Fan Zhang, Lu Han, Shan Bai, Tiedong Sun, Tomoaki Karaki, and Masatoshi Adachi
(K,Na)NbO_{3} (KNN) particles were successfully prepared by hydrothermal synthesis. The results showed that Na^{+} reacted more readily with Nb to form NaNbO_{3} than K^{+}. For the purpose of obtaining KNN particles with K/Na=1, a mixed alkaline solution with K^{+}/Na^{+} ratios ranging from 3.5/1 to 4/1 was required as a starting solution. The morphology and size of KNN particles synthesized strongly depended on K/Na ratio in the KNN particles. The KNN particles synthesized from the starting alkaline solution with K^{+}/Na^{+}=3.5/1 were the smallest with a pelletlike morphology affected by NaNbO_{3}- and KNbO_{3}-based particles. Surfactants such as sodium dodecylbenzenesulfonate (SDBS) and sodium hexametaphosphate (SH) were used to synthesize well dispersed and small KNN particles. Platelike KNN particles with 100 nm thickness and 1.5 µm width were obtained in this study.

Depolarization Temperature Shift of Li_{0.08}Na_{0.92}NbO_{3} Lead-Free Piezoelectric Ceramics by High-Electric-Field Poling

2008-09-19T12:10:00+09:00

Authors: Rintaro Aoyagi, Akihiro Takeda, Makoto Iwata, Masaki Maeda, Takashi Nishida, and Tadashi Shiosaki
The increase in depolarization temperature induced by the poling of (Li_{x}Na_{1-x})NbO_{3} ceramics having an Li concentration of x = 0.08 (LNN8) was studied. Initially, the Curie temperature T_{C} was measured to be approximately 300 °C, and it increased after the application of poling at high electric fields; this increase in Curie temperature depended on the poling conditions employed. When poling was performed at 120 °C at an electric field of 5 kV/mm for 5 min, there was no change in T_{C} and the depolarization temperature was slightly lower than T_{C}. However, both these temperatures increased up on poling at a higher electric field. The X-ray diffraction patterns obtained suggested that the domain volumes of the ceramics were altered by poling at a high electric field and that this structural change caused a change in depolarization temperature.

C-axis-Oriented (Sr,Ca)_{2}NaNb_{5}O_{15} Multilayer Piezoelectric Ceramics Fabricated Using High-Magnetic-Field Method

Hiroyuki Shimizu, Yutaka Doshida, Satoshi Tanaka, and Keizo Uematsu — 2008-09-19T12:10:00+09:00

Authors: Hiroyuki Shimizu, Yutaka Doshida, Satoshi Tanaka, and Keizo Uematsu
We formed a c-axis-oriented (Sr,Ca)_{2}NaNb_{5}O_{15} (SCNN) sheets using a rotation magnetic field, and succeeded in realizing a c-axis-oriented SCNN multilayer piezoelectric ceramic (O-MLPC). The Lotgering factor of both the c-axis-oriented SCNN sheet and inner piezoelectric ceramic of the O-MLPC were approximately 0.80 after sintering. The applied voltage dependences of displacement for both the O-MLPC and a conventional multilayer piezoelectric ceramic (MLPC) with randomly oriented ceramics were examined. As a result, we confirmed that the displacement characteristic of the O-MLPC increased up to a value 2.5 times larger than that of the MLPC.

Vibration Control of Piezoelectric Lead Zirconate Titanate Ceramics Using Negative Capacitance

2008-09-19T12:10:00+09:00

Authors: Jun Takarada, Kenji Imoto, Ken Yamamoto, Munehiro Date, Eiichi Fukada, and Yoshiro Tajitsu
We report on the results of an experiment on the damped vibration process of a lead zirconate titanate (PZT) bimorph connected to a negative-capacitance circuit (NCC), which acts as a capacitor with negative capacitance. NCCs are of two types: a soft NCC that softens the piezoelectric material, and a hard NCC that hardens the piezoelectric material. It was found that the amplitude and the damping time constant of the damped vibration of PZT ceramics connected to a hard NCC change markedly compared with those of PZT ceramics not connected to a hard NCC. In particular, the damping time constant becomes very small. The result suggests that the PZT ceramics become very viscous when connected to a hard NCC.

A Shear-Mode Ultrasonic Motor Using Potassium Sodium Niobate-Based Ceramics with High Mechanical Quality Factor

Enzhu Li, Hirofumi Kakemoto, Takuya Hoshina, and Takaaki Tsurumi — 2008-09-19T12:10:00+09:00

Authors: Enzhu Li, Hirofumi Kakemoto, Takuya Hoshina, and Takaaki Tsurumi
(K,Na)NbO_{3}–LiNbO_{3}–CuO lead-free piezoelectric ceramics that show a high mechanical quality factor Q_{m} were synthesized and used as a drive element of an ultrasonic motor. The Q_{m} of the (K,Na)NbO_{3} ceramic could be enhanced by chemical modification using Li and Cu as well as microstructure control to obtain ceramics with fine grains. The grain size dependence of the Q_{m} was consistent with a model based on the formation of internal bias field to stabilize the domain structure. A shear mode was used to drive the ultrasonic motor because the piezoelectric d_{31} and d_{33} constants of the ceramics were not sufficient for the motor applications. A shear-mode motor driven with four piezoelectric ceramic plates was developed using the lead-free ceramics with a high Q_{m} of 1400, a high d_{15} of 207 pC/N, and a high k_{15} of 0.72. The highest revolution speed of 486 rpm was achieved at 34.5 kHz with the input voltage of approximately 180 V_{p–p} (peak to peak).

Simulation and Fabrication of Embedded Capacitors in the Multilayer Printed Circuit Board

Hee-Wook You, Se-Ho Kim, and Jung-Hyuk Koh — 2008-09-19T12:10:00+09:00

Authors: Hee-Wook You, Se-Ho Kim, and Jung-Hyuk Koh
Embedded system technology can improve electrical performance and reduce assembly cost compared with those discrete component technologies. In this paper, simulation and characterization of embedded capacitors will be presented. The embedded capacitors were simulated and characterized employing eight layered printed circuit boards. Fabrication process of multilayer embedded capacitors will be presented. Theoretical considerations regarding the embedded capacitors have been paid to understand the frequency dependent impedance behavior. Frequency dependent impedances, capacitances, and quality-factors of fabricated embedded capacitors were investigated. As a result, parasitic inductance was developed mainly through via holes and it has almost same value regardless of different capacitances. Frequency dependent capacitance values of fabricated embedded capacitors were well matched with those of simulated embedded capacitors. Temperature dependent capacitance and loss tangent of fabricated embedded capacitor were presented.

Phase Shift of a Coplanar Waveguide by Bias Voltage on Thick Lead Zirconate Titanate Film at Microwave Frequency

Kouji Shibata, Takashi Iijima, and Yoichiro Masuda — 2008-09-19T12:10:00+09:00

Authors: Kouji Shibata, Takashi Iijima, and Yoichiro Masuda
A coplanar waveguide was fabricated by depositing a 1-µm-thick Au film on a multilayer dielectric, consisting of a 2-µm-thick lead zirconate titanate (PZT) film over an Al_{2}O_{3} substrate, through etching. Following this, the reflection constant, transmission constant, and phase variation were measured for this transmission line as bias voltage was varied from 30 to 50 V. As a result, it was confirmed that the phase variation becomes about 15° at a 50 V bias at a frequency of 10 GHz. We then confirmed the basic input-output characteristics of this type of structure in the microwave band. Finally, the relative permittivity of a PZT thick film as a coplanar waveguide was estimated using the measurement results of relative permittivity according to the split cavity resonator method, and phase variation under the condition in which a bias voltage was applied.

Crystal Structural Characterization and Microwave Dielectric Properties of Ca(Ta_{2-x}Nb_{x})O_{6} Ceramics

Akinori Kan and Hirotaka Ogawa — 2008-09-19T12:10:00+09:00

Authors: Akinori Kan and Hirotaka Ogawa
The effects of Nb substitution for Ta on crystal structures and the microwave dielectric properties of Ca(Ta_{2-x}Nb_{x})O_{6} (CTN) ceramics were investigated in this study. The X-ray powder diffraction (XRPD) patterns of CTN ceramics with the composition x ranging from 0 to 1 show a single phase, which corresponds to an orthorhombic phase with an aeschynite-type structure (space group: Pnma), whereas those of the samples with compositions higher than x=1.5 are indexable to an orthorhombic phase with a columbite-type structure (space group: Pbcn). In the composition range of 1.1–1.4, the two phases coexist in the CTN ceramics. As for the covalencies of CTN ceramics, those of the Ca–O and Ta/Nb–O bonds strongly depend on the crystal structure. In addition, the microwave dielectric properties of CTN ceramics significantly varied at compositions ranging from 1 to 1.5, depending on the weight fraction of the aeschynite and columbite phases. As a result, the microwave dielectric properties of CTN ceramics at x=1.5 showed a Q·f of 102,500 GHz with a ε_{r} of 16 and a τ_{f} of -56 ppm/°C. Moreover, a near zero τ_{f} value was obtained at x=1.25 because of the coexistence of the aeschynite and columbite phases.

Microwave Dielectric Properties of Ca_{0.8}Sr_{0.2}TiO_{3}–Li_{0.5}Sm_{0.5}TiO_{3} Ceramics with Near-Zero Temperature Coefficient of Resonant Frequency

Kang Yan, Naoto Shiichi, Tomoaki Karaki, and Masatoshi Adachi — 2008-09-19T12:10:00+09:00

Authors: Kang Yan, Naoto Shiichi, Tomoaki Karaki, and Masatoshi Adachi
The structural evolution and microwave dielectric properties of (1-x)Ca_{0.8}Sr_{0.2}TiO_{3}–xLi_{0.5}Sm_{0.5}TiO_{3} (x=0–1.0) solid solutions were investigated. Most samples exhibit the single orthorhombic perovskite structure and a homogeneous microstructure with high density except for the composition with x=0.5 which included a small amount of the TiO_{2} phase. Increasing Li_{0.5}Sm_{0.5}TiO_{3} content results in a structural change in symmetry around x=0.8. A-site ordering structures were observed in compositions with x≥0.80. The dielectric constant (ε_{r}) decreased with increasing x. The quality factor (Q×f) decreased first up to x=0.5 with increasing x, then increased again up to x=0.82, and then decreased as x increased to x=1.0. The temperature coefficient of the resonant frequency (τ_{f}) decreased from high positive values to negative values with increasing x. A near zero τ_{f} was achieved at x=0.81. Optimized microwave dielectric properties were estimated to be ε_{r}=95, Q×f=3303 GHz, and τ_{f}=-1.8 ppm/°C at x=0.81.

Analysis of Dielectric Response of TiO_{2} in Terahertz Frequency Region by General Harmonic Oscillator Model

2008-09-19T12:10:00+09:00

Authors: Naoki Matsumoto, Tadasu Hosokura, Keisuke Kageyama, Hiroshi Takagi, Yukio Sakabe, and Masanori Hangyo
The terahertz range dielectric response of polycrystalline TiO_{2} (rutile) ceramics and rutile single crystals were investigated by analyzing infrared-active phonons by both Fourier-transform far-infrared (FT-FIR) reflectivity measurement and terahertz time-domain spectroscopy (THz-TDS). The dielectric functions at room temperature measured by THz-TDS are well expressed using the general harmonic oscillator model. We found that the imaginary part of the dielectric permittivity of the TiO_{2} ceramic is threefold higher than that of the rutile single crystal at 300 K. The large dielectric loss is attributed to the additional damping of the A_{2u} mode or/and an increase in the phonon damping. The low-temperature dielectric loss of the rutile single crystals is exceedingly low. However, TiO_{2} ceramics shows little temperature dependence. These results indicate that extrinsic scattering significantly affects the dielectric loss of the TiO_{2} ceramics in the THz region.

Quality Factor of Forsterite for Ultrahigh Frequency Dielectrics Depending on Synthesis Process

Minato Ando, Hitoshi Ohsato, Isao Kagomiya, and Tsutomu Tsunooka — 2008-09-19T12:10:00+09:00

Authors: Minato Ando, Hitoshi Ohsato, Isao Kagomiya, and Tsutomu Tsunooka
Forsterite is a candidate ultrahigh frequency dielectric for wireless communications. The quality factor Q of forsterite (Mg_{2}SiO_{4}) for microwave dielectrics is affected by calcination conditions. The shape of calcined powder particles remains the same as that of fine grains of raw silica materials. This is one of the key points for high Q, because of the realization of a high green density. From the observation of the section of calcined grains by definition (EPMA), it was clarified that Si ions remain in the core part of the grains. The remaining silica affected Q by forming a glassy phase and enstatite (MgSiO_{3}).

Generation of Two Self-Pumped Phase-Conjugated Waves at 532 nm by Nanosecond Pulsed Laser

Hiroshi Miyao, Mihoko Wakui, and Masafumi Yamashita — 2008-09-19T12:10:00+09:00

Authors: Hiroshi Miyao, Mihoko Wakui, and Masafumi Yamashita
Self-pumped phase-conjugated (SPPC) images produced by two SPPC beams generated from a single nanosecond-pulsed laser beam are successfully obtained at beam power ratios of up to 4:1. The two SPPC beams are incident on opposite faces [(-100) and (100)] of a photorefractive barium titanate (BaTiO_{3}) crystal, and the SPPC images are reproduced on the respective crystal faces with high quality due to the reduced interference between the two SPPC beams owing to the delay between the nanosecond pulses of each beam. The quality of the images and the maximum power ratio at which both images are observable are superior to the continuous-wave configuration.

First-Principles Study of Lead-Free Piezoelectric SnTiO_{3}

Yoshitaka Uratani, Tatsuya Shishidou, and Tamio Oguchi — 2008-09-19T12:10:00+09:00

Authors: Yoshitaka Uratani, Tatsuya Shishidou, and Tamio Oguchi
We perform first-principles electronic structure calculations for the lead-free perovskite SnTiO_{3}. Structural optimization is carried out to get the stable tetragonal P4mm structure. Frozen-phonon calculation shows the lattice instability at the centrosymmetric tetragonal P4/mmm structure and the local stability of the P4mm structure. By using the Berry-phase method, the electric polarization and the piezoelectric coefficients are evaluated and found to be comparable with those of PbTiO_{3}.

Brillouin Scattering Studies of Dynamics of Polar Nanoregions in Pb[(In_{1/2}Nb_{1/2})_{0.65}Ti_{0.35}]O_{3} Single Crystals

V. Sivasubramanian, Shinya Tsukada, and Seiji Kojima — 2008-09-19T12:10:00+09:00

Authors: V. Sivasubramanian, Shinya Tsukada, and Seiji Kojima
The dynamical properties of polar nanoregions have been investigated in Pb[(In_{1/2}Nb_{1/2})_{0.65}Ti_{0.35}]O_{3} single crystals by Brillouin scattering. Longitudinal acoustic phonons begin to show softening below the Burns temperature T_{B}∼700 K. The Brillouin shift in the longitudinal acoustic phonon mode exhibits clear anomalies at the cubic–tetragonal phase transition temperature of around T_{ct}∼550 K and at the tetragonal–rhombohedral one of around T_{tr}∼460 K. Broad and narrow central peaks begin to appear below T_{B} and the intermediate temperature T^{*}∼600 K, respectively. Relaxation rate was calculated in the longitudinal phonon mode and central peaks. Below T^{*}, the relaxation rate calculated from the longitudinal phonon mode agrees well with that of the broad central peak, suggesting the coupling between local polarization and strain fluctuations due to the formation of long-lived polar nanoregions. The polarization of the central peaks in the cubic phase suggests that polar nanoregions have the tendency to form long-range polar ordering.

Electron Charge Density Study of (Na_{1-x}K_{x})NbO_{3} in Cubic Structure

2008-09-19T12:10:00+09:00

Authors: Chikako Moriyoshi, Jun-ichi Kato, Yoshihiro Terado, Satoshi Wada, Masaki Takata, and Yoshihiro Kuroiwa
The electron charge density study by synchrotron-radiation powder diffraction has been performed for the cubic structure of (Na_{1-x}K_{x})NbO_{3} (NKN: 0≤x≤1) at 1000 K to investigate the atomic substitution effect on chemical bonding. Our precise analysis using the maximum entropy method (MEM)/Rietveld method demonstrates that the covalent bonding is formed on the Nb–O bond whereas the Na/K atoms are ionic in the entire composition range. The thermal motion of the Na ion in NaNbO_{3} is fairly larger than that of the K ion in KNbO_{3}. The charge density distributions around the O atoms in NaNbO_{3} are extended in the directions perpendicular to the Nb–O bond, which can be related to the rotational mode of the Nb–O_{6} octahedron driving the antiferroic phase transition. No such anisotropy is clearly observed in KNbO_{3} around the O atoms. These behaviors are closely related to the change in the tolerance of the perovskite structure caused by the atomic substitution.

Phase Diagram of Mixed Crystals of Bi_{4-x}Sm_{x}Ti_{3}O_{12}

2008-09-19T12:10:00+09:00

Authors: Makoto Iwata, Akihiro Toya, Rintaro Aoyagi, Masaki Maeda, and Yoshihiro Ishibashi
Phase transitions in Bi_{4-x}Sm_{x}Ti_{3}O_{12} single crystals in the Sm concentration range of x≤0.61 were studied. The phase transition near 670 °C was found to remain almost unchanged in the concentration range of 0≤x≤0.61. Below the transition temperature of 670 °C, dielectric anomaly showing phase transitions was found in BSmT-x, depending on the concentration x. It was confirmed that the triggered transition from the tetragonal phase to the monoclinic phase, observed in Bi_{4}Ti_{3}O_{12}, splits into two phase transitions by adding Sm cations, i.e., from the tetragonal phase to the orthorhombic phase and further to the monoclinic phase. The temperature-concentration phase diagram of the BSmT-x system was clarified.

Dielectric Properties and Phase Transition in CaCu_{3}Ti_{4}O_{12} at High Temperatures

Akira Onodera, Masaki Takesada, Keiichi Kawatani, and Shogo Hiramatsu — 2008-09-19T12:10:00+09:00

Authors: Akira Onodera, Masaki Takesada, Keiichi Kawatani, and Shogo Hiramatsu
The dielectric properties and structural behavior of perovskite-related CaCu_{3}Ti_{4}O_{12} were studied at high temperatures. The dielectric constant increases gradually with increasing temperature and shows a shoulder-like round anomaly at approximately 630 K at 10 kHz. At 732 K, a new dielectric anomaly was found, where the peak value of the dielectric constant, ε_{peak}\simeq2.8×10^{6} at a frequency of 10 kHz. The lattice constant and X-ray intensity of the (880) reflection also exhibit an anomaly at 732 K. These findings indicate that CaCu_{3}Ti_{4}O_{12} undergoes a structural phase transition at 732 K.

Magnetic Properties of Optical Quantum Transition Line Shapes and Line Widths of Electron–Piezoelectric Potential Phonon Interacting Materials under Circularly Oscillating Fields

Joung Young Sug, Su Ho Lee, Jun Yong Choi, Geon Sa-Gong, and Jong Jae Kim — 2008-09-19T12:10:00+09:00

Authors: Joung Young Sug, Su Ho Lee, Jun Yong Choi, Geon Sa-Gong, and Jong Jae Kim
We study optical quantum transition line shapes (QTLSs) and optical quantum transition line widths (QTLWs) in relation to magnetic-field dependence properties of the electron–piezoelectric potential phonon interaction system. We consider two systems — one is subject to right circularly oscillating external fields and the other is subject to left circularly oscillatory external fields. The main purpose of this work is to compare QTLSs, which indicate absorption power, in the two oscillating external fields. Our results indicate that the QTLSs of right circularly oscillating external fields is larger than the QTLSs of left circularly oscillating external fields, while the opposite result is obtained for the QTLWs.

Recent articles in Jpn. J. Appl. Phys.

Preparation of BaTiO_{3} Films on Si Substrate with MgO Buffer Layer by RF Magnetron Sputtering

Fabrication of BaTiO_{3} Thin Films Using Modified Chemical Solutions and Sintering Method

Oxygen Sensing Properties of SrTiO_{3} Thin Films

Fabrication of (Ba_{0.6},Sr_{0.4})TiO_{3} Thick Films by Aerosol Deposition Method for Application to Embedded Multilayered Capacitor Structures

Effect of Interface Structure on Electrical Properties of (Ba,Sr)TiO_{3} Thin Films on Glazed Alumina Substrate

Microwave Tunable Devices Composed of Coplanar Waveguide Line with (Ba_{0.6},Sr_{0.4})TiO_{3}/Au/Cr/(Ba_{0.6},Sr_{0.4})TiO_{3} Sandwich Structure

Epitaxial Growth and Ferroelectric Properties of PbTiO_{3} Nanoislands and Thin Films Grown on Single-Crystalline Pt Films

Raman Spectroscopy Study of Oxygen Vacancies in PbTiO_{3} Thin Films Generated Heat-Treated in Hydrogen Atmosphere

Origin of Compressive Residual Stress in Alkoxide Derived PbTiO_{3} Thin Film on Si Wafer

Rapid Crystallization of Sol–Gel-Deposited Lead Zirconate Titanate Thin Films by 2.45 GHz Microwave Irradiation

Low-Temperature Crystallization of PbZr_{0.3}Ti_{0.7}O_{3} Film Induced by High-Oxygen-Pressure Processing

A Ferroelectric Gate Field Effect Transistor with a ZnO/Pb(Zr,Ti)O_{3} Heterostructure Formed on a Silicon Substrate

Microelectromechanical Systems-Based Electrostatic Field Sensor Using Pb(Zr,Ti)O_{3} Thin Films

In-Plane Lattice Strain Evaluation in Piezoelectric Microcantilever by Two-Dimensional X-ray Diffraction

Electrooptic and Piezoelectric Properties of (Pb,La)(Zr,Ti)O_{3} Films with Various Zr/Ti Ratios

Electro-optic Anisotropy of Epitaxially Grown (Pb,La)(Zr,Ti)O_{3} Films Fabricated by Modified Sol–Gel Process

Effect of Eu/Sr Ratios on Ferroelectric and Fluorescent Properties of Eu-Substituted Strontium Bismuth Tantalate Films

Effects of Electron-Cyclotron-Resonance Oxygen Plasma Irradiation on Properties of Insulator/Ge-Semiconductor Interfaces Prior to Germanium Nitride Formation

Langmuir–Blodgett Fabrication of Nanosheet-Based Dielectric Films without an Interfacial Dead Layer

Effects of Flat HfO_{2} Films Derived from Diethanolamine Solution on Structure and Properties of Metal/Ferroelectrics/Insulator/Semiconductor

Development of Pt/MgO(100) Buffer Layers for Orientation Control of Perovskite Oxide Thin Films

Effect of Mn Substitution for Multiferroic BiFeO_{3} Probed by High-Resolution Soft-X-ray Spectroscopy

Annealing Temperature Dependences of Ferroelectric and Magnetic Properties in Polycrystalline Co-Substituted BiFeO_{3} Films

Rhombohedral–Tetragonal Phase Boundary with High Curie Temperature in (1-x)BiCoO_{3}–xBiFeO_{3} Solid Solution

Crystal Structure and Electrical Properties of {100}-Oriented Epitaxial BiCoO_{3}–BiFeO_{3} Films Grown by Metalorganic Chemical Vapor Deposition

Composition Dependence in BiFeO_{3} Film Capacitor with Suppressed Leakage Current by Nd and Mn Cosubstitution and Their Ferroelectric Properties

Local Structure of BiFeO_{3}–BaTiO_{3} Mixture

Effect of Oxygen Vacancies on Charge Ordered Structure in YFe_{2}O_{4-δ}

Magnetic and Dielectric Properties of HoFe_{2}O_{4} and R_{1-x}R'_{x}Fe_{2}O_{4} (R, R': Rare Earths)

Modification of Ferroelectric Properties of BaTiO_{3}–CoFe_{2}O_{4} Multiferroic Composite Thin Film by Application of Magnetic Field

Domain Size Effect on Dielectric Properties of Barium Titanate Ceramics

Preparation of Highly Dispersed Barium Titanate Nanoparticles from Barium Titanyl Oxalate Nanoparticles and Their Dielectric Properties

Synthesis and Dielectric-Magnetic Properties of Rare-Earth (La, Nd, Sm)-Modified Bi_{4}Ti_{3}O_{12}

High-Performance Bi_{0.5}Na_{0.5}TiO_{3} Single Crystals Grown by High-Oxygen-Pressure Flux Method

Preparation of Inkjet-Printed NiO Films for Ba(Ti,Zr)O_{3}-Based Ceramics and Application to Multilayer Ceramics with Ni Electrodes

Characteristic Pressure Dependence of Spontaneous Polarization in Ferroelectric Liquid Crystal

Helical Structure in Antiferroelectric Liquid Crystals

Electrically Controlled Piezoelectric Motion of Piezoelectric Chiral Polymeric Fibers

Preparation and Properties of BaTiO_{3} Ceramics by Spark Plasma Sintering

Effects of Pressure on Piezoelectric and Dielectric Responses of Relaxor Ferroelectric Solid Solution Pb(Mg_{1/3}Nb_{2/3})O_{3}–PbTiO_{3} Binary System Ceramics near a Morphotropic Phase Boundary Composition

Giant Transverse-Mode Electromechanical Coupling Factor and Piezoelectric Strain in Relaxor Single-Crystal Plates Evaluated Using P–E Hysteresis Loop

Piezoelectric Properties of (Bi_{1/2}Na_{1/2})TiO_{3}-Based Solid Solution for Lead-Free High-Power Applications

Fabrication of High-Density (Bi,La)(Zn,Mg,Ti)O_{3}–PbTiO_{3} Solid Solutions with Ferroelectric and Piezoelectric Functionalities by Microstructural Control

Synthesis of KNbO_{3} Piezoelectric Ceramics Using Citrate Precursors

Synthesis of Nondoped Potassium Niobate Ceramics by Ultrasonic Assisted Hydrothermal Method

Preparation of Barium Titanate–Potassium Niobate Solid Solution System Ceramics and Their Piezoelectric Properties

Hydrothermal Synthesis of (K,Na)NbO_{3} Particles

Depolarization Temperature Shift of Li_{0.08}Na_{0.92}NbO_{3} Lead-Free Piezoelectric Ceramics by High-Electric-Field Poling

C-axis-Oriented (Sr,Ca)_{2}NaNb_{5}O_{15} Multilayer Piezoelectric Ceramics Fabricated Using High-Magnetic-Field Method

Vibration Control of Piezoelectric Lead Zirconate Titanate Ceramics Using Negative Capacitance

A Shear-Mode Ultrasonic Motor Using Potassium Sodium Niobate-Based Ceramics with High Mechanical Quality Factor

Simulation and Fabrication of Embedded Capacitors in the Multilayer Printed Circuit Board

Phase Shift of a Coplanar Waveguide by Bias Voltage on Thick Lead Zirconate Titanate Film at Microwave Frequency

Crystal Structural Characterization and Microwave Dielectric Properties of Ca(Ta_{2-x}Nb_{x})O_{6} Ceramics

Microwave Dielectric Properties of Ca_{0.8}Sr_{0.2}TiO_{3}–Li_{0.5}Sm_{0.5}TiO_{3} Ceramics with Near-Zero Temperature Coefficient of Resonant Frequency

Analysis of Dielectric Response of TiO_{2} in Terahertz Frequency Region by General Harmonic Oscillator Model

Quality Factor of Forsterite for Ultrahigh Frequency Dielectrics Depending on Synthesis Process

Generation of Two Self-Pumped Phase-Conjugated Waves at 532 nm by Nanosecond Pulsed Laser

First-Principles Study of Lead-Free Piezoelectric SnTiO_{3}

Brillouin Scattering Studies of Dynamics of Polar Nanoregions in Pb[(In_{1/2}Nb_{1/2})_{0.65}Ti_{0.35}]O_{3} Single Crystals

Electron Charge Density Study of (Na_{1-x}K_{x})NbO_{3} in Cubic Structure

Phase Diagram of Mixed Crystals of Bi_{4-x}Sm_{x}Ti_{3}O_{12}

Dielectric Properties and Phase Transition in CaCu_{3}Ti_{4}O_{12} at High Temperatures

Magnetic Properties of Optical Quantum Transition Line Shapes and Line Widths of Electron–Piezoelectric Potential Phonon Interacting Materials under Circularly Oscillating Fields