Effect of chemical element doping and sintering atmosphere on the microwave dielectric properties of barium zinc tantalates

The microwave dielectric properties, long range ordering (LRO) of Zn/Ta sit es, and extra phase formation were studied in Ba(Zn-1/3 Ta-2/3)O-3 ceramics doped with 0-4 mol% BaWO4 under varying sintering conditions. The sinterin g atmosphere was either air or ZnO-powder muffling. The LRO were analyzed b y Rietveld refinement method using X-ray diffraction data. The Q.f values w ere extremely low for samples prepared under ZnO-muffling regardless of the degrees of LRO. Maximum Q.f values were 160,000-200,000 GHz at 0.5-1.5 mol % BaWO4 doping. The extra phases formed during sintering in air and under Z nO-muffling were analyzed in detail. The air sintered specimens showed Ba7T a6O22 as a major extra phase accompanied by ZnO-loss; in ZnO-muffled specim ens BaWO4 was a dominant extra phase. During the ZnO-loss process point def ects in the Zn/O sites could be introduced into BZT. (C) 2001 Elsevier Scie nce Ltd. All rights reserved.