Thermal behavior in ferroelectric SrBi2Ta2O9 thin films

Specific heat and X-ray diffraction of Bi-layered perovskite SrBi2Ta2O9 and Bi-rich Sr0.8Bi2.2Ta2O9 thin films prepared by the sol-gel method were measured from room temperature to 800 K. The specific heat of stoichiometric SrBi2Ta2O9 film shows one slight anomaly at 520 K (T-c). In Sr0.8Bi2.2Ta2O9 films, the ferroelectric T-c shifted to 620 K and an additional shoulder in C-p was observed at 410 K (T*). The X-ray diffraction of Sr0.8Bi2.2Ta2O9 films showed structural changes at T* and T-c This evidence suggests the existence of a new intermediate phase in Bi-rich Sr0.8Bi2.2Ta2O9.