Dielectric tunable properties of Ba_0.5Sr_0.5TiO₃–MgMoO₄ composite ceramics for microwave applications

Abstract

(1−x) Ba_0.5Sr_0.5TiO₃–xMgMoO₄ (x = 0, 5, 10, 20 and 30 wt%) composite ceramics were prepared via solid state reaction processing. Their structure and dielectric properties were systematically characterized. The introduction of MgMoO₄ resulted in a change in lattice constant of the perovskite phase and partial reaction between MgMoO₄ and Ba_0.5Sr_0.5TiO₃ occurred in the sintering process. Both X-Ray Diffraction (XRD) and Back-scattered Electron Images (BEI) analysis show the co-existence of three phase structures of BST, MgMoO₄ and BaMoO₄. With increasing of MgMoO₄ content, the tunability of the composite ceramics was decreased due to the increase of the amount of non-ferroelectric phases. The Curie temperature Tc of the samples gradually shifted to low temperatures with increasing of MgMoO₄ content. Dielectric constant can be adjusted in the range from 2035 to 150, meanwhile maintain a relatively high tunability and Q values. The sample with 20 wt% MgMoO₄ possesses a tunability of 10 %, a low dielectric constant of 111 and an appropriate Q value of 183 (2.240 GHz), which meet the requirements of high power and impedance matching, thus making it a promising candidate for applications as electrically tunable microwave devices.