Effect of excess TiO2 on the phase evolution and densification of sol-gel derived (Ba,Sr)TiO3 powders

Nanoscaled (Ba2/3Sr1/3)Ti1+xO3 powders have been prepared by sol-gel technique. Their phase evolution and densification behaviors have been studied by differential thermal analysis (DTA) and high temperature dilatometer, respectively. It is found the addition of 2 mol%-excess amount of TiO2 lowers the activation energy required for the formation of the perovskite phase by about 130 kJ/mol and thus lowers the crystallization temperature of BST powders. However, the excess amount of TiO2 makes the nano-powder difficult to sinter. Transmission electron microscopy reveals that a metastable nano-porous layer has formed on the surface of TiO2-excess nanopowder and this may account for the slow densification rate.