Satoshi Wada

Role of structure gradient region on dielectric properties in Ba(Zr,Ti)O3–KNbO3 nanocomposite ceramics

Crystal structures of KNbO3 (KN)/BaZrxTi1−xO3 [BZT, (0.1 ≤ x ≤ 1)] nanocomposite ceramics have been investigated using synchrotron radiation X-ray powder diffraction, where BZT nanoparticles thinly coated with KN crystals through the heteroepitaxial interface are sintered. The Rietveld analysis based on the multicomponent model reveals that the ceramic grain has the core/multishell structure consisting of a BZT core, distorted BZT and KN multishells. The variations of the volume ratio of the distorted BZT shell region corresponding to the structure gradient interface region and the dielectric property of the ceramics show similar trends as a function of x. From these results, we propose that the structure gradient region is electrically soft, and provides a crucial contribution to the dielectric properties of the nanocomposite ceramics.

Preparation of titanium metal/barium titanate composites with boundary layer structure by hydrothermal method and their dielectric properties

To develop metal/insulator composite capacitors with a high effective dielectric constant, we focus on the microstructure of boundary layer (BL) capacitors. Titanium metal/barium titanate (Ti/BT) composites consisting of Ti metal grains and BT boundary nanolayers were successfully prepared from pressed Ti-BT core–shell particle compacts by a hydrothermal method below 230 °C. In this hydrothermal method, BT polycrystalline shell layers connected to each other by crystal growth via a dissolution and reprecipitation mechanism in barium hydroxide [Ba(OH)2] aqueous solutions. The thickness of BT boundary layers may increase with an increase in the Ba(OH)2 concentration and determine electrical properties. These Ti/BT composites prepared in 250 and 500 mmol/dm3 Ba(OH)2 solutions exhibit effective dielectric constants of over 5000 and 3000, and loss tangents below 0.075 and 0.060 in the frequency range of 100 Hz–100 kHz at room temperature, respectively.

Ferroelectric and piezoelectric properties of (Ba 0.7 Ca 0.3 )(Ti 1−x Sn x )O 3 lead-free ceramics

The ferroelectric and piezoelectric properties of Sn⁴⁺ modified (Ba_0.7Ca_0.3)(Ti_1-xSn_x)O₃, (with x = 0.000 to 0.100 in steps of 0.025) lead free electroceramics were investigated. With Sn⁴⁺ substitution, a structural phase transition from pure tetragonal to pseudo-cubic structure has been observed; which strongly influence the ferroelectric/ piezoelectric nature of the samples. At room temperature, all the samples exhibit typical polarization-electric field hysteresis as well as field induced strain butterfly loop which confirms the ferroelectric and piezoelectric nature. As Sn⁴⁺ content increases, the ferroelectric properties seems to be suppressed while the piezoelectric properties gets improved up to x = 0.075 and then decreased. Moderately high remanent polarization (P_r) and low coercive field (E_c) were observed for all compositions, which may be essential for storage and switching applications.