Papers by Author: Takashi Iijima

Abstract: Lead-free ferroelectric (Bi_0.5Na_0.5)TiO₃ (BNT) thin films were prepared by chemical solution deposition. BNT and Mn-doped BNT precursor thin films crystallized in the perovskite single phase at 700 °C on Pt/TiO_x/SiO₂/Si substrates. The leakage current density of the perovskite BNT films, especially in the high applied field region, was reduced by doping with a small amount of Mn. Also, Mn doping markedly improved the ferroelectric properties of the films. 0.5 and 1.0 mol% Mn-doped BNT thin films exhibited well-shaped ferroelectric polarization (P) electric field (E) hysteresis loops at room temperature. Furthermore, the 1 mol% Mn-doped BNT films showed a typical field-induced strain loop, and the effective d₃₃ values were estimated to be about 60 pm/V.

Abstract: Barium titanate (BaTiO3, BT) – bismuth titanate magnesium oxide (Bi(Mg0.5Ti0.5)O3, BMT) solid solution system ceramics were prepared by conventional sintering method in pursuit of the enhancement of the BT Curie temperature (TC, 132 °C). Normal ferroelectric polarization vs. electric-field (P-E) hysteresis loops were observed for BT-BMT ceramics with BMT contents below 20 and above 60 molar%. On the other hand, broad P-E double hysteresis loops were observed for BMT contents from 30 to 50 molar%. The origin was investigated using synchrotron XRD measurement and Rietveld analysis. The crystal structure was assigned to ferroelectric phase with domain-pinning by certain defect structures. A modified phase diagram was proposed on the basis of the temperature dependence of the crystal structure.

Abstract: Barium titanate (BaTiO3, BT) – bismuth lanthanum zinc titanium oxide [(BiyLa1-y)(Zn0.5Ti0.5)O3, ByL1-yZT] solid solution ceramics were prepared to enhance Curie temperature (TC) of BT, 132 °C, to 200 °C. As the raw materials, nanoparticles were used to make sintering temperatures lower. Optimization of calcination and sintering conditions resulted in a formation of a perovskite single-phase, and their densities were always greater than 94 %. The synchrotron XRD measurement revealed that the crystal structures were assigned to rhombohedral 3m. Temperature dependence of dielectric property revealed that for the 0.5BT-0.5BZT ceramics, TC was 230 °C. Moreover, La-doping into BT-BZT ceramics resulted in decrease of TC significantly. Finally, their piezoelectric properties were measured by electric-field dependence of strain at room temperature, and for the 0.6BT-0.4BZT ceramics, the apparent d33 was measured at 250 pC/N.

Abstract: Bi4Ti3O12 based thick films were prepared by screen printing and firing using Pt bottom electrodes and ZrO2 substrates. The influence of excess Bi2O3 as sintering aid was investigated. Furthermore, substitution of Ti-site and Bi-site for V5+ and Nd3+ was performed. Screen-printable pastes were prepared by kneading the Bi4Ti3O12 based powder and Bi2O3 powder in a three-roll mill with an organic vehicle. The microstructures and ferroelectric properties of the thick films were examined in comparison with bulk ceramics. The remanent polarization of 9.6 μC/cm2 and coercive field of 64 kV/cm were obtained for the Bi3.0Nd1.0Ti2.99V0.01O12 thick film with 10 wt% of excess Bi2O3 fired at 1200OC.