Papers by Author: Masatoshi Adachi

Abstract: CaBi4Ti4O15 based thick films were prepared by screen-printing method on Si substrates. Screen-printable pastes were prepared by kneading the CaBi4Ti4O15 powder in a three-roll mill with an organic vehicle. The remanent polarization of 6.3 C/cm2 and coercive field of 130kV/cm were obtained for the CaBi4Ti4O15 with Nb2O5 1wt% thick film fired at 1130°C. The cavity structure was prepared by etching of Si substrate. The displacement-electric field butterfly curves were obtained.

Abstract: In order to prepare lead free multi-layer ceramic (MLC) actuators with Ni inner electrodes, inkjet ink containing NiO was prepared and its rheological properties were examined. The viscosity of the ink followed the Andrade's equation. By using this ink, Ba(Ti,Zr)O3 based MLCs were prepared. The printed NiO layers were reduced to metal Ni and they functioned as the inner electrodes. The remanent polarization of the MLCs increased with the grain growth caused by the increase of firing temperature. The remanent polarization Pr and coercive field Ec of the MLCs fired at 1400°C were 6.4 μC/cm2 and 3.5 kV/cm, respectively. The displacement of the MLCs with 7 active layers was approximately 320nm at 30 kV/cm. The effective d33 shows approximately 160 pm/V when the electric field was 10 kV/cm.

Abstract: MBi4Ti4O15 (M=Ba,Ca) thick films were prepared by screen printing and firing using Pt bottom electrodes and ZrO2 substrates. Screen-printable pastes were prepared by kneading the MBi4Ti4O15 powder in a three-roll mill with an organic vehicle. The microstructures and electric properties of the thick films were examined in comparison with bulk ceramics. The remanent polarization of 6.2 9C/cm2 and coercive field of 130kV/cm were obtained for the CaBi4Ti4O15 thick film fired at 1130OC. The Curie points of MBi4Ti4O15 (M=Ba,Ca) thick films from dielectric peaks were 450OC and 790 OC for M=Ba and M= Ca.

Abstract: Barium titanate (BaTiO3) ceramics with a high-density were fabricated by two-step sintering method from hydrothermally synthesized 100 nm BaTiO3 nano-particles. The best specimen with an average grain size of 1.6 μm and a density of 5.91 g/cm3 (98.3% of the theoretical value). The dielectric constant was 4500 and electromechanical coupling factor kp was 45%. Large piezoelectric constants d33 = 460 pC/N and d31 = -185 pC/N were observed in the specimens. This was an important practical result towards obtaining a high d33 in non-lead-based BaTiO3 ceramics manufactured by a low-cost process. These results also indicated the possibility of using BaTiO3 ceramics in piezoelectric devices at room temperature. Temperature dependence of dielectric constant showed two peaks located at 24 and 126 oC, corresponding to orthorhombic-to-tetragonal phase transition temperature Tot and Curie temperature Tc, respectively. Owing to the size effect of nanocrystals, Tot shifted to 24 oC. The maximum of electromechanical coupling factor kp appeared close to the phase transition temperature. It also caused a very large temperature coefficient of resonance frequency from room temperature to 60 oC. Hysteresis curve measurement showed a very low coercive field Ec = 115 V/mm. A large Poisson’s ratio, about 0.38, was determined from the ratio of overtone frequency and resonant frequency in the planar mode. The high Poisson’s ratio and the large dielectric constants are most likely the origin of the high piezoelectric constants in the ceramics.

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.

Abstract: [BaO]m(Ti0.975Zr0.025)O2 ceramics with Ni electrodes were prepared by a firing in N2 atmosphere. The dielectric, ferroelectric and piezoelectric properties were examined in terms of the composition. The remanent polarization of 9.5μC/cm2 was obtained for m=1.01 by the addition of 0.5wt% SiO2. The longitudinal piezoelectric constant d33 calculated from a unipolar signal (8kV/cm,10Hz) was 430pC/N. Lead-free multi-layered piezoelectric actuators were fabricated using this material by the tape casting, screen-printing of Ni electrodes, laminating under heat and pressure, and firing in N2 atmosphere. The displacement of the actuator with 75μm x 9 active piezoelectric layers was 0.17μm at an applied voltage of 75V and a frequency of 10Hz.

Abstract: Piezoelectric actuators were prepared by the screen printing of piezoelectric thick films and the wet etching of Si substrates for the application of ink jet printer heads. The Pt bottom electrode was used as the vibration plate to obtain a large displacement. The layer structure and integration processes of the Pt bottom electrodes were investigated to be suited to the whole preparation process of the piezoelectric actuator. The displacement of the center of the actuator with 100 μｍ x mm was 0.03 μm at the applied voltage of 30 V and frequency of 4 kHz.