Intragrain compositional gradient barium strontium titanate ceramics fabricated by a sol-assisted sintering technology

Our previous researches show that (Ba,Sr)TiO₃(BST) ceramics with intragrain compositional gradients possess increased temperature stability, and a sol-assisted sintering technique can significantly reduce the sintering temperature and this favors the further improvement of the ceramic properties. Before sintering, preforms consisting of the mixture of barium titanate (BT) and strontium titanate (ST) powders were infiltrated with a BT sol. In this paper, sintering behaviors and compositional gradation, especially at lower sintering temperature for longer holding time were investigated. Dielectric properties were also measured and discussed. The ceramics´ microstructural evolution was examined via scanning electron microscopy. The compositional gradients were studied with X-ray diffraction and energy dispersive spectroscopy. Experimental results showed that the existence of nano-grains formed from the infiltrated sol-gel in the ceramics play a key role in the process of densification. The mechanism of sol-assisted sintering and compositional gradation was experimentally investigated and discussed, which would help to optimize the fabrication scheme. Results suggest that the BST ceramics with intragrain compositional gradients is a promising candidate as tunable microwave elements.