Mapping the P-T phase diagram of high-pressure ferroelectricity in perovskites

The overarching aim of this project is to re-examine the long-debated issue of the pressure-induced inversion symmetry breaking in perovskite oxides. Although this phenomenon is now commonly accepted theoretically, experimental evidence has been elusive, to say the least. The most recent efforts including our own have failed to confirm its occurrence in the most natural candidate and classical ferroelectric perovskite PbTiO3. However, we have realised very recently that KNbO3 (KNO) makes a much better candidate: our first results by room temperature XRD and Raman spectroscopy at high pressures (HP) show that KNO undergoes a phase transition from cubic to tetragonal that is unlike all known perovskites and shows all characteristics expected for the long awaited HP ferroelectric transition. The purpose of this proposal is to extend the phase diagram to low temperatures and map for the first time this original phase boundary with pressure and temperature.