Electroceramics in Japan VIII

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Authors: Tomo Kobayashi, Yuji Noguchi, Masaru Miyayama
Abstract: Intergrowth-structured Bi4Ti3O12-BaBi4Ti4O15 (BiT-BBTi) single crystals were grown by a self-flux method, and the crystal structure and polarization properties were investigated. Transmission electron microscope observations and X-ray diffraction analysis presented direct evidence of the intergrowth structure composed of the alternate stacking of BiT and BBTi layers. The BiT-BBTi crystals showed a giant spontaneous polarization (Ps) along the a axis of 52 μC/cm2, which was larger than those of the crystals of BiT (46 μC/cm2) and BBTi (16 μC/cm2). The large Ps of the BiT-BBTi crystals is suggested to originate from the ferroelectric displacements of the Bi of Bi2O2 layers as well as from the Bi substitution for Ba induced by compositional deviation. It was found that the polarization properties of the BiT-BBTi crystals depend strongly on the composition.
Authors: Masaru Tada, Minoru Osada, Masato Kakihana, Yuji Noguchi, Masaru Miyayama
Abstract: We investigated the influence of photoexcited nonequilibrium electrons in Bi4Ti3O12-d which contains a high density of oxygen vacancies. As increasing oxygen deficiency, the photocurrent undergoes a rapid enhancement, accompanied by a remarkable change of kinetics. In heavily oxygen deficient Bi4Ti3O12-d (d=0.45), we observed dispersive photoconductivity, a behavior resembles with persistent photoconductivity phenomena in some perovskites. We argue that oxygen vacancies acting as trapping centers for electrons are linked to dispersive diffusion in the perovskite blocks, which control carrier recombination.
Authors: Tadashi Takenaka
Abstract: The dielectric, ferroelectric and piezoelectric properties of strontium bismuth tantalate niobate, Sr1-xBi2+xTa2-yNbyO9 [SBTN10x(y)] ceramics were investigated. The samples were fabricated by a conventional ceramic fabrication technique. Curie temperature, Tc, increased with an increase in Nb concentration y, and Tc of SBTN2(y) showed two regions with different slopes that divided near y=1.0. The coercive field, Ec, of SBTN2(y) increased with the increase in y and the highest Ec of 90 kV/cm was obtained. SBTN2(0.6) and SBTN2(1.0) showed the highest coupling factor k33 of 0.17 in the SBTN2(x) system.
Authors: Takashi Takagi, Takashi Fujii, Akira Ando, Yukio Sakabe
Abstract: Piezoelectric properties of potassium niobate (KNbO3; KN) crystal grown using the Vertical Bridgman method were obtained by a resonance-antiresonance method for a length extensional mode. The crystal was poled at 200°C under an electric field of 70 V/mm applied parallel to one of the spontaneous polarization axes. An electromechanical coupling factor (k31) of 0.248, mechanical quality factor (Qm) of 5700, piezoelectric constant (d31) of 9.6 pC/N, elastic compliance (s11E) of 4.02 pm2/ N, and constant (e33T/e0) of 42 were obtained. The optical absorption coefficient of poled crystal has been less than 1.0 cm-1 in the wavelength region of 400-1600 nm. Comparing these values with the reported one for TSSG-KN, indicated that our VB-KN was of good quality.
Authors: Takeru Yoshida, Hajime Nagata, Tadashi Takenaka
Abstract: Doping a small quantity of additive Bi2O3 is effective in suppressing the deliquescence of KNbO3 ceramics. When an optimized ball-milling process was included, dense and nondeliquescent KNbO3 ceramics were obtained by a conventional firing process. However, the presence of Bi prevented grain growth (<0.2 μm) and it was one of the causes of low ferroelectricity. Moreover, the insufficient resistivity made the poling treatment difficult. In order to improve the electric properties, a small quantity of additive MnCO3 was also doped into KNbO3 with 0.5 mass% Bi2O3. Codoping of KNbO3 with MnCO3 and Bi2O3 (abbreviated to KNBixMny; x = 0~1.0, y = 0~1.0 in mass%) improved the ferroelectricity of samples, and it also had an effect on the resistivity and densification of sintered bodies. Well-saturated P-E hysteresis loops were observed with any amount of Mn and the largest remanent polarization Pr was about 16 μC/cm2. The piezoelectric properties of KNBi0.5Mn0.3, which had the highest piezoelectricity in this study, are an electromechanical coupling factor k33 and piezoelectric constant d33 of 0.30 and 101 pC/N, respectively.
Authors: Koichi Yako, Hirofumi Kakemoto, Takaaki Tsurumi, Satoshi Wada
Abstract: Engineered domain configuration was induced into barium titanate (BaTiO3) single crystals, and the d33 piezoelectricity was investigated as a function of domain size. Prior to the domain engineering, the dependence of domain configuration on the temperature and the electric-field was investigated, and above Curie temperature (Tc), when the electric-field over 16 kV/cm was applied along [111]c direction, the fine engineered domain configuration appeared. On the basis of the above information, the 33 resonators with different domain sizes were successfully prepared. Their piezoelectric measurement revealed that the d33 of the 33 resonators with fine-engineered domain configurations were higher than those of BaTiO3 single-domain crystals. Moreover, d33 increased with decreasing domain sizes. The highest d33 of 289 pC/N was obtained in the BaTiO3 crystal with a domain size of 13μm.
Authors: Satoshi Wada, Takuya Hoshina, Hiroaki Yasuno, Masanori Ohishi, Hirofumi Kakemoto, Takaaki Tsurumi, Masatomo Yashima
Abstract: Powder dielectric measurement of barium titanate (BaTiO3) fine particles from 17 to 1,000 nm revealed a maximum dielectric constant at a certain particle size. The sizes with maximum dielectric constants were strongly dependent on preparation methods. When BaTiO3 fine particles were prepared in vacuum of 10-2 torr, a dielectric maximum of 15,000 was observed at 70 nm. On the other hand, when BaTiO3 fine particles were prepared in air, a dielectric maximum of 5,000 was observed at 140 nm. Structure refinement of BaTiO3 particles using a Rietveld method revealed that all of BaTiO3 particles were composed of two parts; (a) surface cubic layer and (b) bulk tetragonal layer. Moreover, a thickness of surface cubic layer for BaTiO3 particles prepared in vacuum was much thinner than that for BaTiO3 particles prepared in air. To explain the differences, a new model on the basis of “surface relaxation” was proposed.
Authors: Tatsuo Sakashita, Kentaro Nakamura, Giuseppe Pezzotti, Hirokazu Chazono
Abstract: Residual stresses in Ni-MLCC were investigated by Raman microprobe piezo-spectroscopic (PS) methods. The shape of the Raman spectrum of BaTiO3 in Ni-MLCC depended on the angle between the polarizing direction of the incident laser beam and the direction of the internal electrode. From a set of precise calibrations, we show that the orientation dependence arises from the interaction between internal stresses and the polycrystalline microstructure; by taking into account such an orientation dependence, we were able to establish a technique for the measurement of the distribution of residual stresses in Ni-MLCC.
Authors: Takeshi Kobayashi, Jiunnjye Tsaur, Masaaki Ichiki, Ryutaro Maeda
Abstract: Flat PZT cantilevers have been successfully fabricated from the Pt/Ti/PZT/Pt/Ti/SiO2/SOI multi-layered structure through MEMS technologies. A displacement of the tip of the cantilever driven at 6 V is measured to be 7.6 μm and the transverse piezoelectric constant calculated from the displacement is –103 pm/V. 1D optical scanners have been designed, simulated, fabricated and tested. The rotation angles of the mirror of the scanners were 60-70% of the simulated values.
Authors: Tomoya Ohno, Masayuki Fujimoto, Hisao Suzuki
Abstract: This paper describes the deposition of PZT thin films on soda-lime glass substrate with ITO bottom electrode by CSD (Chemical Solution Deposition). The transmittance of the obtained PZT thin film on ITO/glass substrate was about 60 % in the visible light region. The deposited transparent PZT thin film exhibited the ferroelectricity of Pr=36.3 μC/cm2 and Ec=71.3 kV/cm. In addition, the piezoelectric property of the resultant PZT thin film was relatively large and exhibited the measured effective d33 of 120 pC/N after the polarization.

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