X-ray absorption spectroscopy on titanate perovskites at the Ti K edge

The Ti K edge X-ray absorption has been measured under high pressure at room temperature for ATiO3 perovskites (A = Ca, Sr, Ba and Pb). The pre-edge features have been used to determine the local distortion around the Ti atom as a function of applied features. The ferroelectric local instability decreases when pressure is increased (PbTiO3 ) and eventually vanishes at high pressure (BaTiO3 ). The antiferrodistorsive instability remains unchanged under pressure for CaTiO3 and appears above 5 GPa for SrTiO3 . Moreover, it is shown that at room pressure SrTiO3 was locally ferroelectric. A new phase appears for SrTiO3 above 14 GPa with a strong deformation of the oxygen octahedron