EFFECT OF ORDERING-INDUCED DOMAIN BOUNDARIES ON LOW-LOSS BA(ZN1 3TA2/3)O-3-BAZRO3 PEROVSKITE MICROWAVE DIELECTRICS/

Small substitutions of BaZrO3 into Ba[(Zn,Ni)(1/3)Ta-2/3]O-3 are utili zed in the commercial preparation of low-loss perovskite microwave die lectrics, The structures of a series of these phases with substitution levels ranging from 1% to 5% BaZrO3 were examined using high-resoluti on TEM. For less than or equal to 2.15% BaZrO3 the solid solutions ret ain the ordered ''1:2'' structure of the Ba[(Zn,Ni)(1/3)Ta-2/3]O-3 end -member but are comprised of small ordered domains whose size decrease s as the Zr content is raised, The decrease in the size of the domains parallels a decrease in the processing time required to access a low- loss state, Although for pure Ba[(Zn,Ni)(1/3)Ta-2/3]O-3 reductions in the degree of cation order produce a large increase in the dielectric loss, the Zr-substituted ceramics retain a very low loss, We believe t he low losses of the 1:2 ceramics are derived from the stabilization o f the ordering-induced domain boundaries via the partial segregation o f the Zr cations, For substitutions between 3% and 5% BaZrO3 the size of the ordered domains continues to decrease but the system undergoes an abrupt transformation to a cubic ''1:1'' ordered structure with a d oubled perovskite repeat. The structures of these phases have been int erpreted using a ''random layer'' model in which one site is occupied by Ta and the other by a random distribution of Zn, Zr, and the remain ing Ta cations, i.e., Ba{[Zn(2-y/3)Ta(1-2y/3)Zr-y](1/2)[Ta-1/2]}O-3. A lthough the ordering is confined to-nano-sized domains, these ceramics also exhibit low losses, again reflecting the relative stability of t he domain boundaries. In this case we believe the low losses reflect t he effectiveness of the random layer in stabilizing the anti-phase bou ndaries.