Toshihiro Okamatsu

The Effect of Rare Earth (Ln = Gd, Dy, Y and Yb) Doping on the Microstructure and Reliability in BaTiO3-Based Monolithic Ceramic Capacitors (MLCs)

The effect of rare earth (Ln = Gd, Dy, Y and Yb) and Mg ions on the microstructure and reliability of BaTiO3-based monolithic ceramic capacitors (MLCs) with Ni electrodes was investigated. The X-ray diffraction results about the lattice volume of sintered specimens suggested that Gd and Dy ions predominatly substituted into the Ba-site, Yb ions gave exclusive substitution at the Ti-site, while Y ions occupied either the Ba- and Ti-site. The reliability of ceramic capacitors was increasing with increasing the ionic radius of the rare earths in this study. The nonlinearity coefficient() etsimated from the leakage currents and the lifetime measured from the highly accelerated lifetime testing (HALT) showed a negative correlation which was observed only from Dy and Y ions doped specimens. The quantity of Ln and Mg in the grains tended to increase with increasing the Ln ionic radius. In order to improve the reliability and the insulation property of BaTiO3 based MLCs with Ni electrodes, it is important that acceptor ions at the Ti-site compensate donor ions which are rare earth ions at the Ba-site, so the overall quantity of the dopants required for the charge compensation with acceptor and donor ions increases accordingly.

Effects of Grain Boundary and Segregated-Phases on Reliability of Ba(Ti,Zr)O3-Based Ni Electrode MLCs

The reliability in the highly accelerated life test (HALT) for multilayer ceramic capacitors (MLCs) composed of the Ba(Ti,Zr)O3-Gd-Mg-Mn-Si system was markedly improved by controlling the amount of SiO2 and the ratio of Ba/(Ti+Zr). We observed the following characteristics in the microstructures when the reliability was improved. 1) The segregated-phases, which consisted of Mg oxides and Si oxides, were dispersed well in the dielectric layers and their size was considerably small. 2) The corrosion resistance of grain boundaries was improved. 3) The electric potential as a contrast in the focused ion beam scanning ion microscopy was homogeneous in both the grains and the grain boundaries. We can design these microstructures by controlling the additives to generate BaMg2Si2O7 and BaSi2O5, which have low melting points.

Structural Characteristics of (Ba0.94Gd0.06)(Ti0.97Mg0.03)O3 in Cubic Structure Determined by High-Energy Synchrotron-Radiation Powder Diffraction

Structural study by high-energy synchrotron-radiation powder diffraction has been performed for (Ba0.94Gd0.06)(Ti0.97Mg0.03)O3 (BGTM) at 473 K to investigate the substitution effects of Gd and Mg on the cubic structure of BaTiO3. Our precise electron-density analysis using the maximum entropy method (MEM)/Rietveld method demonstrates that the bonding electron density between the Ti and O atoms in BGTM decreases with the substitution of Gd and Mg elements, which provides a significant contrast to the fact that the Ti–O bond length is shortened in BGTM. No obvious change is observed on the Ba–O ionic bonding. It is considered that the lowering of the cubic–tetragonal phase transition temperature in BGTM is attributed to the decrease in covalency on the Ti–O bond in BGTM. The features of thermal motions of the constituent atoms are discussed on the basis of the mean square thermal displacement parameters by taking account of the chemical bonding nature and tolerance factor of the BaTiO3 system.