Pressure-induced γ → α-NaTiOPO4 phase transition

The effect of applied pressure on α- and γ-NaTiOPO4 (NaTP) was studied at wide temperature range using the X-ray diffraction technique. Neither a phase transition nor a noticeable cell volume decrease was observed for the α-NaTP polymorph up to 8 GPa, even when heating up to 1073 K. The applied pressure retains the γ-NaTP structural topology up to 8 GPa for r.t. experiments, although a 4% decrease of cell volume had been observed. Hot pressing was found to provoke the γ-NaTP → α-NaTP phase transformation, starting at 773 K and 4.45 GPa. A complete transition has been observed at 873 K and 7.7 GPa. A mechanism for the pressure-driven γ-NaTP → α-NaTP phase transition has been proposed.