Dielectric properties of 0.7BaO·0.3SrO·(1 − y)TiO2·yNb2O5 composite ceramics

The 0.7BaO·0.3SrO·(1 − y)TiO2·yNb2O5 (BSTN) composite ceramics with both the perovskite and the tungsten bronze phases were successfully prepared by controlling some excessive contents of components and traditional ceramic process where 0.1 < y < 0.7. The phase composition and dielectric properties of the composite ceramics were investigated by XRD and LCZ Meter. According to the results, the dielectric properties of the BSTN have both characteristics of the perovskite phase and the tungsten bronze phase. The ɛr and tan δ of the BSTN depend on the relative content of the perovskite phase as well as the solubility of Nb5+ ions in it. The samples in which two phases coexist clearly have higher dielectric constant than the samples that only contain one solid solution, but the tan δ of those two phases coexisting is also higher. The ɛr and tan δ decrease with the increase of applied frequency for same composition. In the BSTN composite ceramics, the phase transition temperature of the tungsten bronze phase depends on the solubility of Ti4+ ions in the phase and the relative content of the perovskite phase. The lowest transition temperature is around 200 °C and it is about 90 °C lower than the pure tungsten bronze phase Sr0.3Ba0.7Nb2O6.