Microstructure and dielectric properties of Ba0.6Sr0.4TiO3–MgAl2O4 composite ceramics

Abstract (1 −  x )Ba 0.6 Sr 0.4 TiO 3 – x MgAl 2 O 4 ( x  = 25, 30, 35 and 40 wt%) composite ceramics were prepared by conventional solid-state reaction method. The microstructures, dielectric properties and tunability of the composites have been investigated. The XRD patterns analysis reveals two crystalline phases, a cubic perovskite structure Ba 0.6 Sr 0.4 TiO 3 (BST) and a spinel structure MgAl 2 O 4 (MA). SEM observations show that the BST grains slightly dwindle and agglomerate with increasing amounts of MA. A dielectric peak with very strong frequency dispersion is observed at higher MA content, and the Curie temperature shifts to a higher temperature with increasing MA content. The ceramic sample with 30 wt% MA has the optimized properties: the dielectric constant is 1503, the dielectric loss is 0.003 at 10 kHz and 25 °C, the tunability is 23.63% under a dc electric field of 1.0 kV/mm, which is suitable for ferroelectric phase shifter.