Evidence of ferroelectricity in metastable Sm2Ti2O7 thin film

Abstract

The synthesis by the sol–gel route of metastable Sm₂Ti₂O₇ thin film is reported. While for standard conditions of pressure and temperature, the Sm₂Ti₂O₇ compound crystallizes in a cubic/pyrochlore structure, in the form of a thin film (grown on (110)-oriented SrTiO₃ substrate), a monoclinic/layered perovskite structure is stabilized by strain effects induced by the substrate. Under these conditions, (00l)-oriented Sm₂Ti₂O₇ oxide is isostructural to ferroelectric Ln₂Ti₂O₇ (with Ln = La, Ce, Pr and Nd) phases, which is already well known. Studies by Selected Area Electron Diffraction (SAED) reveal the existence of a systematically twinned structure and the presence of a fault in the stacking of the perovskite layers. Piezoresponse Force Microscopy (PFM) measurements confirm undoubtedly the ferroelectricity in this metastable phase.