Clarification of the Phase Diagram of PbHfO 3 in Pressure-temperature Space

We report the high-temperature and high-pressure single-crystal x-ray diffraction study of PbHfO3. The increase of pressure enables an additional intermediate phase, located between the cubic and incommensurate phases, and characterized by superstructure reflections indicating the presence of anti-phase oxygen octahedral tilts. The temperature-dependent diffuse peak at an incommensurate position is much better pronounced at higher pressures (~ 2 GPa) than at lower pressures (~ 1.1 GPa), which we interpret as enhancing of the incommensurate soft mode on pressure increase. Several peculiarities in the behavior of superstructural reflections at M- and X- points are reported and discussed.