Effect of lead additive on the ferroelectric properties and microstructure of Sr_xPb_yBi_2zTa₂O₉ thin films

Ferroelectric thin films of bismuth-containing layered perovskite Sr_xPb_yBi_2zTa₂O₉ have been prepared using the metalorganic decomposition method. The effect of both Sr and Pb content on the crystal structure, microstructure, and ferroelectric properties of Sr_xPb_yBi_2.3Ta₂O₉ films was investigated. A maximum remanent polarization of 2P_r=19.2μC/cm² was obtained for the Sr_xPb_0.2Bi_2.3Ta₂O₉ film with 20 mol % Sr-deficient composition as prepared at 800°C, which could be the compromising effects of Sr content on both grain growth and second phase formation of BiTaO₄. The substitution of Pb for Bi is accompanied by the occurrence of oxygen vacancies to compensate the charge balance, which is responsible for grain growth mechanism in Sr_0.8Pb_0.2Bi_2.3Ta₂O₉ films. Fatigue endurance of Sr_0.8Bi_2.3Ta₂O₉ films becomes problematic after 10⁹ cycles with a decrease in remanent polarization to 85% of the original value. This phenomenon was related to electron injection and creation of electron traps due to the occupation of Sr vacancies by Bi cations. It is demonstrated that the fatigue endurance of Sr_0.8Bi_2.3Ta₂O₉ film can be improved by doping with 20 mol % PbO.