Dielectric tunable properties of Ba_(0.5)Sr_(0.5)TiO_3-MgMoO_4 composite ceramics for microwave applications

摘要

(1 -x) Ba_(0.5)Sr_(0.5)TiO_3-xMgMoO_4 (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 MgMoO_4 resulted in a change in lattice constant of the perovskite phase and partial reaction between MgMoO_4 and Ba_(0.5)Sr_(0.5)TiO_3 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, MgMoO_4 and BaMoO_4. With increasing of MgMoO_4 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 MgMoO_4 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% MgMoO_4 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.