Upward ferroelectric self-poling in (001) oriented PbZr0.2Ti0.8O3 epitaxial films with compressive strain

Upward self-poling phenomenon was observed in PbZr0.2Ti0.8O3 ferroelectric films which were grown on (001) SrTiO3 substrate with either p-type La0.7Sr0.3MnO3 or n-type SrRuO3 buffered layer, or on n-type (001) Nb-SrTiO3 substrate. Both upward self-poling and epitaxial strain are strong in the super-thin PbZr0.2Ti0.8O3 epitaxial films, while they become weak and finally disappear in thick epitaxial films or thin epitaxial films with high-density oxygen vacancies. Besides, both of them disappear in PbZr0.2Ti0.8O3 polycrystalline films on Pt/TiO2/SiO2/Si substrate. Therefore, the main origin of upward self-poling is epitaxial strain rather than p-n/Schottky junction or charged vacancies in PbZr0.2Ti0.8O3 epitaxial films here.