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 sites, and extra phase formation were studied in Ba(Zn1/3Ta2/3)O3 ceramics doped with 0–4 mol% BaWO4 under varying sintering conditions. The sintering atmosphere was either air or ZnO-powder muffling. The LRO were analyzed by Rietveld refinement method using X-ray diffraction data. The Q·f values were 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 ZnO-muffling were analyzed in detail. The air sintered specimens showed Ba7Ta6O22 as a major extra phase accompanied by ZnO-loss; in ZnO-muffled specimens BaWO4 was a dominant extra phase. During the ZnO-loss process point defects in the Zn/O sites could be introduced into BZT.