Structural and ferroelectric properties of tantalum-doped bismuth titanate thin films prepared by sol-gel method

Bi₄Ti_2.96Ta_0.04O₁₂ (BTTO) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by sol-gel method. The effects of Ta-substitution and annealing temperature (500-800°C) on the microstructure and ferroelectric properties of Bi₄Ti₃O₁₂ thin films were investigated. X-Ray diffraction analysis reveals that the intensities of (117) peaks are realitively broad and weak at annealing temperatures smaller than 700°C. With the increase of annealing temperature from 500°C to 800°C, the grain size of BTTO thin films increases. The BTTO thin films annealed at 700°C exhibit the highest remanent polarization (2P_r) of 40 μC/cm² and lowest coercive field (2E_c) of 120 kV/cm. It is obvious that the measured 2P_r of the BTTO thin film is larger than that of Bi₄Ti₃O₁₂ thin films (2P_r=25 μC/cm²) The improved ferroelectric properties can be attributed to the substitution of Ta⁵⁺ to Ti⁴⁺ in Bi₄Ti₃O₁₂ assisted the elimination of defects such as oxygen vacancy and vacancy complexes.