Evidence of ferroelectricity in metastable Sm2Ti2O7 thin film

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 Ln(2)Ti(2)O(7) (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.