Symmetry degeneration and room temperature ferroelectricity in ion-irradiated SrTiO 3

Polar phonon modes associated with room temperature ferroelectricity are observed in SrTiO single crystals irradiated with Ti ions. Quantitative strain analysis reveals that irradiation-induced out-of-plane strain drives the centrosymmetric cubic SrTiO to a tetragonal-like structure in the maximum damaged region. Energy transfer from ions to electrons during ion irradiation yields defects in SrTiO that also plays an important role for the room temperature ferroelectricity. Different from thin film techniques, the ferroelectricity in the ion irradiated SrTiO can occur for much larger thicknesses, depending on the energy and type of ion.