Effect of sintering additives on the densification and dielectric properties of Sr0.5Ba0.5Nb2O6 ceramics synthesized by a soft-chemistry method

Abstract

Nano-crystalline Sr0.5Ba0.5Nb2O6 powders with addition of LiNbO3 or LiF as sintering additives were prepared bya soft-chemistry synthesis using polyethylene glycol. Calcination at 600 ?C results in nanocrystalline powders(dcryst. ? 30 nm) which were sintered between 1000 and 1300 ?C to ceramic bodies. By addition of 10 and 20 mol% LiNbO3, the sintering temperature was reduced by about 200 K and the activation energy of the initial stage ofsintering decreases from 386 to 271 kJ mol?1. The sintering aid improves the grain growth and dense ceramicbodies were obtained after sintering at 1125 ?C for 1 h. A higher LiNbO3 content favors the formation of a pillarlikemicrostructure. XRD patterns of ceramics sintered above 1000 ?C show only reflections of the Sr0.5Ba0.5Nb2O6phase indicating an incorporation of LiNbO3 in the Sr0.5Ba0.5Nb2O6 structure. Dielectric measurements reveal adiffuse phase transition and a relaxor-like behavior. The phase transition temperature (Tm) depends on the sinteringconditions and is between 117 and 127 ?C for 10 mol% LiNbO3, which is very close to pureSr0.5Ba0.5Nb2O6, while addition of 20 mol% shifts Tm to around 200 ?C and the transition becomes slightly morediffuse. The optical band gap of the samples is ? 3.3 eV and depends slightly on the sintering conditions. We alsotried LiF as sintering aid, but this leads to the formation of considerable amounts of secondary phases in theceramics and relative densities of only 82%.