Effects of Al2O3 on dielectric properties of core–shell Ba0.7Sr0.3Ti0.9925Tm0.0103@Al2O3 ceramics

Abstract

The sol-gel method and conventional sintering were used to prepare Ba0.7Sr0.3Ti0.9925Tm0.01O3(BST) and core–shell-structured BST@Al2O3 ceramics. The microstructure and phase composition of the BST and BST@Al2O3 were examined using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results indicated that an amorphous Al2O3 film with a thickness of approximately 5–15 nm was coated on the BST cores. No new phase was observed in the BST@Al2O3 powder and ceramics with a single perovskite structure. The grains of the BST@Al2O3 ceramics were refined by the coated Al2O3. When the Al2O3 content was <5 wt%, the dielectric constant of the BST@Al2O3 ceramics remained above 200000 at a low frequency of 0.12 kHz and above 8000 at 200 kHz. The dielectric loss was significantly reduced compared to that of BST. The Curie peak of the BST@Al2O3 ceramics was broadened, and the Curie temperature of the BST@Al2O3 ceramics decreased. Thus, dielectric materials with high dielectric constants and low dielectric losses were successfully prepared, and a wide and flattened Curie peak was observed for BST@Al2O3 ceramics.