Preparation And Nonlinear Dielectric Properties Of Ba_0.6Sr_0.4TiO₃/MgO Composites Ceramics

Ferroelectric Ba_xSr_1-xTiO₃ solid solutions have considerable dielectric nonlinearity. This desired property makes them promising candidate materials for tunable devices in microwave communication technology such as phase shifter. In this work, Ba_0.6Sr_0.4TiO₃ powder was prepared by a citrate method, and the yielded powder and MgO nano-powder were used to prepare composite ceramics with nominal composition of Ba_0.6Sr_0.4TiO₃+xwt%MgO (x=10-60). The effects of sintering temperature and composition on the structure, densification and dielectric properties have been investigated with the purpose of enhancing the sinterability and nonlinear dielectric properties of the composites.Ba_0.6Sr_0.4TiO₃ powder was synthesized by using a citrate method. The contributing factors to the phase purity and morphology of the products have been examined. It was found that superfine and uniform Ba_0.6Sr_0.4TiO₃ powder can be produced by calcining at 650℃.The effects of sintering temperature on the structure, densification behavior and dielectric properties have been exploited. It has been demonstrated that the reactive Ba_0.6Sr_0.4TiO₃ and MgO powders allow a relatively low densification temperature for Ba_0.6Sr_0.4TiO₃/MgO composite ceramics. The preferred sintering temperature has been ascertained to be 1230℃based on the dielectric property data, with the specimens sintered at this temperature attaining relatively high relative densities of 94.3%-96.3%.The effects of composition on the structure and dielectric properties have been inspected. The results indicated that increasing the relative content of MgO led to a decline of the dielectric constant and the loss along with a degradation of the dielectric nonlinearity. A preferred composition was determined to be Ba_0.6Sr_0.4TiO₃+60wt%MgO in terms of the dielectric property data. The composition shows a dielectric constant of 416 and a dielectric loss of 0.1% at 10 kHz, a tunability of 17.5% under 10 kHz and 20.0 kV/cm bias together with a figure of merit of 129.