Domain microstructures and ferroelectric phase transition in Pb0.35Sr0.65TiO3 films studied by second harmonic generation in reflection geometry

Abstract

Second harmonic generation (SHG) measurements were performed in the reflection geometry using the femtosecond Ti:sapphire laser at the wavelength of 810nm for Pb0.35Sr0.65TiO3 films, which were epitaxially deposited on (001) MgO substrates by pulsed laser ablation under different oxygen pressures. We formulated the procedures to measure the ratios of the compensated fractions of both c domains and in-plane domains and the ratios of the components of the nonlinear susceptibility tensor under only a non-normal incidence of the fundamental beam. We applied this technique to characterize the domain microstructures of the Pb0.35Sr0.65TiO3 films at three typical temperatures (78, 150, and 300K) and found these films to exhibit a larger compensated fraction of c domains. The ratios of the components of the nonlinear susceptibility tensor were calculated to be relatively constant regardless of the temperature and the oxygen pressure. On the other hand, their SHG intensities were found to increase as the oxygen pressure goes lower, which is attributed to the higher density of the oxygen vacancies in the films. These films also exhibit the diffuselike phase transition in a very wide temperature range, which is attributed to the structural inhomogeneity and the nonuniform distribution of Pb2+ and Sr2+ in the Pb0.35Sr0.65TiO3 films.