Microwave dielectric properties and thermally stimulated relaxations of Ba0.6Sr0.4La4Ti4O15−TiO2 composite ceramics by flowing oxygen sintering

Abstract

Phase structure, sintering behavior, microwave dielectric properties and thermally stimulated relaxations of the 0.93Ba0.6Sr0.4La4Ti4O15−0.07TiO2 composite ceramics were investigated through using flowing oxygen atmosphere sintering. Ba0.6Sr0.4La4Ti4O15 (BSLT) sintered at 1500 °C possesses microwave dielectric properties of er = 44, Q × f = 45,000 GHz and τ f = −7.5 ppm/°C. Rutile TiO2 with er = 105, Q × f = 46,000 GHz, τ f = +465 ppm/°C was combined with the BSLT to compensate the negative τ f value in current research. XRD reveals that the ceramic samples possess a hexagonal perovskite structure and a secondary phase of TiO2−δ. The 0.93BSLT−0.07TiO2 compounds sintered in flowing oxygen exhibit small grain sizes and some pores, which are less compactly sintered compared with the ones sintered in air. The densification, grain growth and microwave dielectric properties of 0.93BSLT−0.07TiO2 have a clear dependence on sintering temperature. The 0.93BSLT−0.07TiO2 composite ceramics sintered at 1500 °C possess good microwave dielectric properties: er = 47.2, Q × f = 32,400 GHz and τ f = −3.3 ppm/°C. The extrinsic loss mechanism associated with defects was explored by relying on thermally stimulated depolarization current (TSDC) measurement. It can be manifested that TSDC relaxations are mostly derived from oxygen vacancies and TSDC spectra are evidently affected by the sintering temperature.