Second harmonic generation and ferroelectric phase transitions in thick and ultrathin Pb0.35Sr0.65TiO3 films on (001) MgO substrates

Abstract

Second harmonic generation of a 16-nm-thick ultrathin Pb0.35Sr0.65TiO3 film and a 243-nm-thick Pb0.35Sr0.65TiO3 film grown on (001) MgO substrates by pulsed laser deposition is investigated. It is concluded that in the ultrathin film the ferroelectric phase is still present and the diffuse phase transition is absent. In contrast, the thick film exhibits a pronounced diffuse phase transition. Theoretical analysis based on the polarization diagrams shows that the compensated c-domain fraction is dominant in both films whereas the nonlinear susceptibility of the ultrathin film has a different tensor property from the thick film.