Effect of Pyrolysis Atmosphere on Ferroelectric Properties of Bi_3.25La_0.75Ti₃O₁₂ Films Prepared by Sol-Gel Method

The effect of pyrolysis atmosphere is investigated for Bi_3.25La_0.75Ti₃O₁₂ (BLT) films prepared on Pt/TiO₂/SiO₂/p-Si(100) substrates by sol-gel processes. The pyrolysis is carried out at 400°C for 20min under air or O₂ atmosphere and the successive anneal is performed at 700°C for 30min under O₂ atmosphere. The pyrolysis under O₂ is enough for complete removal of organic species, however after pyrolysis under air, carbon and hydrogen atomic species as organic fragment are partly remained in the film. This incomplete removal of organic fragments affects the grain growth and cause more defects in the film or between interfaces during the annealing for the crystallization of BLT film. The growth direction and grain size of the BLT film is revealed to affect ferroelectric properties. The remanent polarization P_r for the BLT films of pyrolysis in O₂ and air are measured to be 18.85μC/cm² and 12.56μC/cm², respectively. The defects degrade the fatigue property dramatically for the film of pyrolysis in air. It can be concluded that the pyrolysis is an important procedure to control ferroelectric properties.