Kenji Uchino

Dielectric and Piezoelectric Properties of 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3 Single Crystals

The dielectric, piezoelectric and elastic properties of 0.91(PbZn1/3Nb2/3)O3–0.09PbTiO3 single crystals have been investigated as functions of temperature and applied electric field. Two multiple phase transitions at 68°C and 178°C, the crystal changing from the rhombohedral ferroelectric phase to tetragonal ferroelectric and then to cubic paraelectric, have been observed. Both the transitions are of first-order, but both are slightly diffused. Significant increases in the dielectric, piezoelectric and elastic constants are observed at the lower transition point. In particular, the sample poled along the pseudo-cubic [001] axis reveals anomalously large piezoelectric and electro-mechanical coupling constants at room temperature in the rhombohedral phase (d[001]//=1500×10-12 C/N, k[001]//=0.92).

Phase transitions in the Pb (Zn1/3Nb2/3)O3-PbTiO3 system

Abstract Two successive phase transitions, changing the crystal symmetry from rhombohedral to tetragonal, and then to cubic on a heating process, have been investigated in the Pb(Zn1/3Nb2/3)O3-PbTiO3 single crystals with the composition near the morphotropic phase boundary. The existence of the morphotropic phase boundary has been confirmed by measuring the dielectric, piezoelectric and pyroelectric constant. Anomalously large electromechanical and piezoelectric constants are observed on the morphotropic phase boundary.

Magnetoelectric Properties in Piezoelectric and Magnetostrictive Laminate Composites

Magnetoelectric laminate composites of piezoelectric-magnetostrictive materials were investigated. The composites were prepared by stacking and bonding Pb(Zr, Ti)O3 (PZT) and Terfenol-D disks. Experimental results indicated that the magnetoelectric voltage coefficient, dE/dH, increased with decreasing thickness and increasing piezoelectric voltage constant (g31) of the PZT layer. We obtained the highest magnetoelectric voltage coefficient of 4.68 V/cmOe at room temperature for the sample with high g33 PZT of 0.5 mm in thickness. This value is about 36 times higher than the best reported value.

Magnetoelectric effect in composites of magnetostrictive and piezoelectric materials

In the past few decades, extensive research has been conducted on the magnetoelectric (ME) effect in single phase and composite materials. Dielectric polarization of a material under a magnetic field or an induced magnetization under an electric field requires the simultaneous presence of long-range ordering of magnetic moments and electric dipoles. Single phase materials suffer from the drawback that the ME effect is considerably weak even at low temperatures, limiting their applicability in practical devices. Better alternatives are ME composites that have large magnitudes of the ME voltage coefficient. The composites exploit the product property of the materials. The ME effect can be realized using composites consisting of individual piezomagnetic and piezoelectric phases or individual magnetostrictive and piezoelectric phases. In the past few years, our group has done extensive research on ME materials for magnetic field sensing applications and current measurement probes for high-power electric transmission systems. In this review article, we mainly emphasize our investigations of ME particulate composites and laminate composites and summarize the important results. The data reported in the literature are also compared for clarity. Based on these results, we establish the fact that magnetoelectric laminate composites (MLCs) made from the giant magnetostrictive material, Terfenol-D, and relaxor-based piezocrystals are far superior to the other contenders. The large ME voltage coefficient in MLCs was obtained because of the high piezoelectric voltage coefficient of the piezocrystals and large elastic compliances. In addition, an optimized thickness ratio between the piezoelectric and magnetostrictive phases and the direction of the magnetostriction also influence the magnitude of the ME coefficient.

Piezoelectric ultrasonic motors : overview

This paper reviews recent developments of ultrasonic motors using piezoelectric resonant vibrations. Following the historical background, ultrasonic motors using standing and traveling waves are introduced. Driving principles and motor characteristics are explained in comparison with conventional electromagnetic motors. After a brief discussion on speed and thrust calculation, finally, reliability issues of ultrasonic motors are described.

Crystal orientation dependence of piezoelectric properties of lead zirconate titanate near the morphotropic phase boundary

The piezoelectric and dielectric constants in different crystal orientations of the lead zirconate titanate (PZT) have been phenomenologically calculated for the compositions near the morphotropic phase boundary at room temperature. For a tetragonal PZT, the effective piezoelectric constant d33 monotonously decreases as the crystal cutting angle from the spontaneous polarization direction [001] increases. However, for a rhombohedral PZT, the effective piezoelectric constant d33[001]// along the perovskite [001] direction was found to be much larger than those along the spontaneous polarization direction [111]. This crystal orientation-related enhancement is emphasized as the composition approaches the morphotropic phase boundary. This suggests that by adopting the perovskite [001] orientation with a rhombohedral composition near the morphotropic phase boundary, the piezoelectric constant d33 for PZT can be greatly enhanced.

Electrostrictive effect in lead magnesium niobate single crystals

Transverse and longitudinal elastic strain have been measured for electric fields applied along the 〈100〉 direction in single crystals of lead magnesium niobate [Pb(Mg1/3Nb2/3)03], using a bonded strain gauge technique. A quadratic electrostrictive relation holds between induced elastic strain and electric polarization for temperatures near the low‐frequency dielectric maximum. The electrostriction coefficients are almost temperature independent with values Q11=2.50×10−2 m4/C2 and Q12=−0.96×10−2 m4/C2. To check the direct measurements, the hydrostatic Q coefficient was determined independently by measuring the pressure dependence of the dielectric permittivity. The value Qh =0.60×10−2 m4/C2 obtained is in good agreement with that calculated from the direct measurements.

Piezoelectric and Magnetoelectric Properties of Lead Zirconate Titanate/Ni-Ferrite Particulate Composites

Piezoelectric and magnetoelectric properties of magnetoelectric particulate composites with Lead Zirconate Titanate (PZT) and Ni-ferrite were investigated. The maximum magnetoelectric voltage coefficient, (dE/dH)max, increased with higher sintering temperature up to 1250°C. Composites sintered at 1300°C, had dissolution of Fe ions into PZT, or interdiffusion between PZT and ferrite. Connectivity of the ferrite particles and sintering temperature were important factors for fabrication of this particulate composite. The composite added with 20 wt.% amount of Ni-ferrite, sintered at 1250°C for 2 hours, had the highest magnetoelectric voltage coefficient of 115 mV/cm · Oe at room temperature. This value is comparable to that of the BaTiO3-CoFe2O4 based composites reported by Philips laboratory, and is 44% higher than other magnetoelectric particulate composites.

Large electrostrictive effects in relaxor ferroelectrics

Lead magnesium niobate and other relaxor ferroelectrics are promising transducer materials for use as active elements in adaptive optic systems and similar applications. These ceramics are dominantly in the paraelectric phase, and dimension control is obtained through the high intrinsic quadratic electrostrictive effect. Since stable ferroelectric domain structures do not occur, the problems of dimensional creep and non-reproducibility (aging and de-aging effects) of the conventional poled piezoelectric ceramic are largely eliminated. Suitably chosen compositions in the Pb3MgNb2O9-PbTiO3 family give electrostriction strains ten times larger than those of conventional BaTiO3-based ceramics. Low expansion coefficients are an added advantage for thermal stability.

Microstructure and piezoelectric properties of 0.95(Na0.5K0.5)NbO3–0.05BaTiO3 ceramics

For 0.95(Na0.5K0.5)NbO3–0.05BaTiO3 (0.95NKN-0.05BT) ceramics sintered at 1040–1075°C, abnormal grain growth occurred but the grain size decreased when the sintering temperature exceeded 1075°C. The dielectric constant (ϵ3T∕ϵ3), electromechanical coupling factor (kp), and piezoelectric constant (d33) were considerably increased with increasing relative density and grain size. Evaporation of Na2O deteriorated the piezoelectric properties by decreasing the resistivity. To minimize Na2O evaporation, specimens were muffled with 0.95NKN-0.05BT powders during the sintering. Improved piezoelectric properties of d33=225pC∕N, kp=36%, and ϵ3T∕ϵ3=1058 were obtained for specimen sintered at 1060°C for 2h with muffling.