Effect of Different Annealing Atmosphere on Ferroelectric Properties of 0.7BiFeO3-0.3PbTiO3 Thin Films

0.7BiFeO3-0.3PbTiO3 (BFPT7030) thin films were deposited on LaNiO3/SiO2/Si substrate by sol-gel process. The thin films were annealed in air, O2 flow, air flow and N2 flow in air environment by a rapid thermal annealing technique. Films annealed in air, O2 flow and air flow were fully crystallized and showed highly (100) preferred orientation. BFPT7030 thin film annealed in N2 flow could not obtain hysteresis loops because of the bad crystallization. The BFPT7030 thin films annealed in air showed the largest Pr of 30 µC·cm−2 and the lowest leakage current density, while the film annealed in air flow showed the lowest Pr of 13 µC·cm−2 and the largest leakage current. XPS results demonstrate that the Fe3+: Fe2+ is 2.09:1, 1.65:1 and 1.5:1 for films annealed in air, O2 flow and air flow, respectively, and the Bi and Pb relative content in the films annealed in O2 flow and air flow is less than that of the film annealed in air. Fluctuation of Fe ions valence state and the volatilization of Bi are the main reasons for the generation of oxygen vacancies. Adding O2 gas is helpful to prevent the generation of oxygen vacancies. Although volatilization of Pb would lead to inferior microstructure, no oxygen vacancies is generated during the process of volatilization of Pb.