Enhanced dielectric tunability of Ba_0.55Sr_0.45TiO₃-ZnAl₂O₄ composite ceramic

(1-x)(Ba,Sr)TiO₃-xZnAl₂O₄ (x=0.00, 0.05, 0.10 and 0.20) composites were prepared by the traditional solid state reaction. The dielectric, tunable and Raman spectroscopy properties are studied. The curie temperature of the composites does not show much difference due to low solubility between BST and ZnAl₂O₄. For the composition with x=0.20, its tunability is up to 46.4% (@2 kV/mm), nearly 1.5 times of that of pure BST, and meanwhile its dielectric constant and loss are decreased. The results imply that making non- or little-soluble BST-nonferroelectric composites is a very effective way to keep high tunability and low dielectric constant simultaneously. Raman results confirm that there are some residual polar microregions in (1-x)BST-xZnAl₂O₄ composite, and their extrinsic contribution to the dielectric tunability is responsible for a deviation from the ε versus E behavior predicted by Johnson's equation.