Sequence of phase transitions in PbHfO3

The temperature changes in the PbHfO 3 structure in the temperature range of 20 < t < 400°C have been studied by X-ray powder diffraction. The sequence of phase changes with an increase in temperature was found to be as follows: orthorhombic phase Pbam (O1), orthorhombic phase C 2 mm (O2), tetragonal phase P 4 mm (T), and cubic phase Pm 3 m (C). The C 2 mm and P 4 mm phases are ferroelectric, which is confirmed by measuring the dependences ɛ( t ). The similarity of the transition pattern obtained with the known transition sequences for ferroelectric (barium titanate, potassium niobate, and lead titanate) and antiferroelectric (lead zirconate) oxides is analyzed.