Barium strontium titanate-based perovskite materials for microwave applications

Ba1−xSrxTiO3 solid solutions were prepared by solid-state reaction from raw materials. Four compositions with x = 0.25, 0.50, 0.75 and 0.90 have been investigated. The perovskite type and polycrystalline structure of the BST samples were revealed by X-ray diffraction data. The morphology, grain size distribution, porous structure and elemental composition of the sintered ceramics were analyzed by using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) microanalysis. The temperature dependence of permittivity and of dielectric loss tangent at low frequency (1 kHz) showed decrease of Curie temperature with increase of Sr content. Microwave measurements (1 GHz) showed substantial decrease of the dielectric constant from about 1600 to 200 and also of the losses from 12% to less than 2% with the Sr concentration increase from x = 0.25 to x = 0.90. Moreover, the addition of MgO and MnO2 1 wt.% each, improved sintering process and lowered the microwave losses up to 0.2%.