Key Engineering Materials Vols. 421-422

Abstract: The Bi0.2K0.8(Zn0.1Ti0.1)Ta0.8O3 and Li doped ceramics prepared via the solid-state reaction technique were investigated. The XRD patterns show the single phase cubic perovskite structure without any evidence of secondary phases when sintered at 1250 oC for undoped Bi0.2K0.8(Zn0.1Ti0.1)Ta0.8O3 and sintered at 1100 oC for Li doped one. The dielectric properties indicate the diffused phase transition (DPT). The dielectric loss of undoped ceramic increases with increasing frequency in temperature range 270 oC down to -150 oC, which suggests low temperature relaxation, while the dielectric loss of Li doped ceramic reveals the interesting lower value over a wide temperature range of about 0 - 300 oC.

Abstract: Apart from aging effect, barium titanate ceramics usually subjected to the mechanical loading when it is used in electronic device. Thus, it is very interesting to investigate the influence of various compressive stresses on ferroelectric aging behavior of Ba(Ti0.99-xFe0.01Nbx)O3 , x=0.005-0.015. In this study, the P-E hysteresis loops were observed by using compressometer in conjunction with a modified Sawyer-Tower circuit. The stress level was varied from 0 to 185 MPa. The results showed that the dissipation energy, saturation polarization (Psat), remnant polarization (Pr) and the coercive field (Ec) decreased with increasing of stress. The aging behavior was still observed in acceptor-dominant of hybrid doped ceramics. The aging was also enhanced under application of the external stress. The explanation based on the defect-dipole and domain-reorientation processes was discussed.

Abstract: In order to investigate the mechanism of hybrid doped ferroelectric, BaTiO3 sample was prepared via conventional mixed-oxide method. The sample was then subjected to doping process with Fe3+ as acceptor dopant and Nb5+ as donor dopant. With varied concentration of acceptor dopant from 0.5 to 1 %M at fixed 1%M of donor, hysteresis property was obtained via Sawyer-Tower circuit. The hysteresis property of the sample was observed to vary over time by influence of ageing effect. By numerical scaling, the stretched exponential decay behavior of the system was obtained to gain the better insight of ageing mechanism of hybrid doped ferroelectric. With stretched exponential fitting, stretching parameter of lower doped Nb5+ were observed lower than that of equivalently doped Nb5+.

Abstract: Nano-sized BaTiO3 powders with narrow size distribution and the high tetragonality were attempted to synthesize by the rotary-hydrothermal process in water system, using two kinds of commercial anatase-type TiO2 (ST21/ST01) with different particle size and Ba(OH)2. The rotary-hydrothermal syntheses were done with the rotary-speed of 20 revolutions per minute at 523 K for 24 h. Highly- and mono-dispersed BaTiO3 powders were successfully synthesized by applying the rotary-hydrothermal process. For rotary-hydrothermal synthesis, it was found that the average size, tetragonality, and quality of the BaTiO3 particle strongly depended on the particle size of the starting material. In the case of using ST01 as a starting material, BaTiO3 nano-powders mainly composed of coarse-faceted particles (average particle size = ca.100 nm) with the tetragonal phase and very little lattice defects were successfully synthesized.

Abstract: Wide band dielectric spectroscopy was applied from kHz to THz region for the analysis of both the ionic and the dipole polarization in Ba0.6Sr0.4TiO3 ceramics. The dielectric permittivity above the dielectric maximum temperature (Tm) is mostly dominated by the ionic polarization, while that below Tm is governed by the dipole polarization. Dielectric permittivity given by the dipole polarization increased and the relaxation frequency decreased with decreasing temperature. These phenomena are related to a increase of the size of polar nanoregions (PNRs).

Abstract: The factors causing a decrease in the resistivity of multilayer ceramic capacitors (MLCCs) with a decrease in the thickness of dielectric layers were examined by carrying out measurements and finite element method (FEM) simulations. The obtained electric field vs. current density plots (E–J characteristics) indicated that the local concentration of electric field increased with the decrease in the thickness of the dielectric layers. The investigation of the local concentration of electric field at the grain boundaries using an FEM showed that the decrease in resistivity was caused by the roughness of the interface between dielectric layers and inner electrodes and the presence of large grains in the dielectric layers.

Abstract: The behavior of hydrogen in (Ba,Sr)TiO3 (BST) thin film capacitors under electric fields was investigated by performing secondary ion mass spectroscopy (SIMS) analyses. It was clearly observed that the ingress of atmospheric hydrogen into BST thin film capacitors occurred through the anode and that it diffused toward the cathode under electric fields. In addition, it was found that the deterioration of the I-V properties of the BST thin film capacitors can be interpreted in terms of the distribution of hydrogen concentration in the BST thin films.

Abstract: An Al2O3-SiO2-PbO-MgO laminated tape system was prepared to investigate the dependence of some physical properties on various sintering temperatures, 840 °C, 880 °C, 920 °C and 960 °C. The results show that the effect of the increasing sintering temperatures was a fluctuating in the density value of the laminates. It was also observed that the dielectric constant and dielectric loss showed the lowest value for the sintering temperature of 880 °C. SEM micrographs of the laminate samples shows a mixture of grain sizes and the samples had a combination of small and large pores with the average grain size around 2.20-2.64 m.

Abstract: Several types of Ag powder were used as electrode paste for a multilayer ceramic substrate. The shrinkage behavior of the silver powders was investigated during the sintering. Bending and cracking were frequently observed on the substrate when coarse powders that show a broad size distribution and aggregation were used. The shrinkage curve of the Ag paste obtained by spray pyrolysis agreed well with that of the substrate. Furthermore, the electrical properties of the Ag paste were also determined. The resistivity of a silver electrode sintered at 900°C was about 2.00×10-6 Ω･cm.

Abstract: BaTiO3 powders with particle size 0.1μm were made by solid state synthesis. To make high tetragonality BaTiO3 powder, mixture of TiO2 and BaCO3 was calcined in vacuum condition. And to make low tetragonality BaTiO3 powder, the mixture was calcined in air condition. With each powder, MLCCs with Ni-internal electrode were fabricated. Relationships between temperature and relative dielectric constant of MLCCs’ dielectric layers were analyzed and their dielectric grains were observed by TEM-EDS. As the result, MLCC made from high tetragonality BaTiO3 powder had good temperature characteristics and core-shell dielectric grains.