Manabu Hagiwara 교수

Dense and phase-pure (Bi1/2K1/2)TiO3 (BKT) ceramics with various average grain sizes from 0.18 to 1.01 μm were prepared from a hydrothermally synthesized powder and their phase transition behaviors were studied by means of dielectric measurements. A drastic increase of the maximum dielectric permittivity (εm) with increasing the grain size was found in the temperature dependence of permittivity. The sample with the largest grain size clearly showed both a frequency dependence of dielectric maxim

The temperature evolution of polar order in an $A$-site complex perovskite $(\mathrm{B}{\mathrm{i}}_{1/2}{\mathrm{K}}_{1/2})\mathrm{Ti}{\mathrm{O}}_{3}$ (BKT) has been investigated by measurements of dielectric permittivity, depolarization current, and stress-stain curves at elevated temperatures. Upon cooling from high temperatures, BKT first enters a relaxor state and then spontaneously transforms into a ferroelectric state. The analyses of temperature and frequency dependence of permittivity

Dense and phase-pure (Bi1/2K1/2)TiO3 (BKT) ceramics with various grain sizes from 0.18 to 1.01 µm were prepared by conventional sintering of a hydrothermally synthesized fine powder. The decrease in grain size resulted in the reductions in tetragonality, remanent polarization, and the piezoelectric d33 coefficient, whereas the room-temperature dielectric permittivity slightly increased with decreasing grain size. The measurement of the temperature dependence of permittivity revealed that BKT exh

The electrical properties of a piezoelectric single crystal of calcium aluminate silicate Ca 2 Al 2 SiO 7 (CAS) were studied at elevated temperatures and its applicability to high-temperature pressure sensors was investigated. The CAS bulk single crystal was grown by the Czochralski method. The piezoelectric d 14 and d 36 constants were respectively evaluated as 6.04 and 4.04 pC/N by the resonance and antiresonance method. The temperature dependence of the piezoelectric constant was investigated

0.6 BiFeO 3 –0.4( Bi 0.5 K 0.5 ) TiO 3 (0.6 BF –0.4 BKT ) ceramic samples with 0.0–4.0 mol% CuO were prepared by the solid‐state reaction. The CuO addition aided the densification of the samples and slightly increased the lattice constant. The relaxor‐like defuse dielectric peak of 0.6 BF –0.4 BKT became sharper with increasing the CuO content. Polarization–electric field curve of the undoped 0.6 BF –0.4 BKT was a pinched loop in the as‐sintered state, while that was a square hysteresis with a l

The electric transient response method is an effective technique to evaluate material constants of piezoelectric ceramics under high-power driving. In this study, we tried to incorporate nonlinear piezoelectric behaviors in the analysis of transient responses. As a base for handling the nonlinear piezoelectric responses, we proposed an assumption that the electric displacement is proportional to the strain without phase lag, which could be described by a real and constant piezoelectric e-coeffic

The effect of the size and morphology of piezoelectric BiFeO₃ particles on the performance of BiFeO₃–PDMS composite generators is revealed.

The delafossite-type CuFeO2 (CFO) is a promising p-type thermoelectric oxide reported to show a large Seebeck coefficient, but the lack of a texturing method for CFO ceramics limits their thermoelectric performance. Here, we show that textured CFO ceramics with an enhanced thermoelectric power factor can be obtained by a facile process based on the reactive templated grain growth (RTGG) method. Nanorods of α-FeOOH were synthesized by a hydrothermal reaction and used as templates for the RTGG pro

Bismuth potassium titanate (Bi1/2K1/2)TiO3 (BKT) with disordered A-site Bi3+ and K+ ions is known to undergo a spontaneous phase transition between a high-temperature relaxor (R) state and a low-temperature ferroelectric (FE) state at around 300 °C. Here, we demonstrate that the thermal history of BKT ceramics has a great effect on the stability of the R and FE states. To modulate the distribution of Bi3+ and K+ ions, as-sintered BKT ceramics were postannealed at 900 °C and then cooled to 500 °C

The nonlinear piezoelectric and dielectric responses in the shear mode against an applied field were investigated using hard and soft Pb(Zr,Ti)O 3 (PZT)-based piezoelectric ceramics. The shear strain was measured using a double-beam leaser Doppler vibrometer. The third-order harmonic components of the strain and the current of soft PZT markedly increased with the increase in the field while those of hard PZT were maintained at low values. In hard PZT, the elastic nonlinearity in the shear mode w

Fine powders of bismuth potassium titanate (Bi1/2K1/2)TiO3 (BKT) synthesized by hydrothermal reactions have been reported to have good sinterability and high chemical stability against long-time sintering. In this study, detailed chemical and structural characterizations were performed on a hydrothermal BKT powder sample to identify the origin of such properties. The results of X-ray diffraction, infrared transmittance, and diffuse reflectance measurements revealed that the hydrothermal BKT part