EFFECT OF STOICHIOMETRY ON THE DIELECTRIC-PROPERTIES AND LIFE PERFORMANCE OF (PB0.875BA0.125)[MG1/3NB2/3)0.5(ZN1/3NB2/3)0.3TI0.2]O3 RELAXOR DIELECTRIC CERAMIC .1. DIELECTRIC-PROPERTIES

Effects of stoichiometry (A/B mole ratio, i.e., the ratio of elements on the A-site to those on the B-site in the perovskite structure) on the dielectric properties and microstructure of a partially A-site substituted relaxor, (Pb0.875Ba0.125)A [(Mg1/3Nb2/3)0.5(Zn1/3Nb2/3)0.3Ti0.2]BO3 were investigated in the A/B range between 0.95 and 1.05. Specimens, with A/B equal to or greater than 1.01, were sintered at lower temperatures than those with A/B equal to or less than 1.00. A maximum dielectric constant (K(max)) value of 13300 was obtained when A/B was 1.01. When A/B was less than 1.01, K(max) decreased, due to the formation of pyrochlore phase. K(max) also decreased with A/B values greater than 1.01, probably due to a grain boundary phase. Resistivity measurements did not suggest a stoichiometry dependence. However, breakdown voltage decreased with an increase in A/B, possibly due to the segregation of PbO with low dielectric constant at grain boundaries.