Abstract
Lead-based relaxor material, Pb(Zn, Nb, Fe, W)O3 for multilayer ceramic capacitors was ground by ball-milling with partially stabilized zirconia balls of 1, 3 and 15mm in diameter in order to examine the effects of particle size on the sintering and dielectric properties. Particle size distribution, contamination from the balls and the residual strain of the powder were examined. The use of small zirconia balls in ball-milling was effective to grind the powder to submicronmeter. Average particle sizes of powders ball-milled for 128 hours using 1, 3, 15mmφ balls were 0.24, 0.35 and 0.68μm, respectively. The structural distortion of the ball-milled powders increased with decreasing particle size in contrast with little change in the lattice strain. The contamination from zirconia balls in ball-milling was examined with fluorescent X-ray analysis, and it was made clear that the ball-milled powders were free from the contamination. The average grain size of sintered ceramics from the fine powder with average particle size of 0.24μm was rather fine than that of sintered ceramics at the same temperature from 0.68μm powder. The densification of the fine powder was enhanced at lower firing temperature, and the dense dielectric ceramics were obtained at the firing temperature of 750°C which was lower by 100°C compared with the optimum firing temperature for the powders with average particle size of about 1μm. Relative permittivity of the fine grained sample fabricated from 0.24μm powder at 750°C was above 104 at room temperature and less DC bias field and less temperature dependences compared to that of coarse grained sample fabricated from the usual powder.
