Investigation Of MO₂(M=Ti, Zr, Mn) Phase Transitions Under High-Pressure And High-Temperature

There have been numerous contradictory results concerning the crystal structures and the phase transitions sequence in MO₂. Based on the facts, we choose representative MO₂ dioxide—rutile(TiO₂), baddeylite(ZrO₂), pyrolusite(MnO₂).Under quasihydrostatic conditions using argon as medium, the pressure-induced phase transitions of MO₂(M= Ti, Zr, Mn) have been investigated by in-situ Raman spectrum method and energy-dispersive X-ray in-situ power-diffraction method with synchrotron in a laser-heated diamond anvil cell (DAC). These experiments were conducted to certain pressure ranges and temperature ranges.In this study , Raman spectrum of orthorhombic (Pbca) structure in TiO₂ and ZrO₂ are presented for the first time based on our experiments respectively.Raman spectrum study under high-pressure and high-temperature in rutile indicates that at room temperature and elevated pressure, the rutile-type TiO₂ begins to transform to baddeleyite-type phase at 13.4GPa, and then the baddeleyite phase transforms to a Pbca phase at 29.4GPa. The formation of Pbca phase from baddeleyite phase needs the condition of high temperature, it transforms back to baddeleyite structure completely at pressure of a little below its formation, which suggests the boundary of the two phases can be determined at about 28 GPa. At room temperature, Pbca phase retains up to 63.4GPa, the highest pressure in this study.The investigation of phase transitions of ZrO₂ under high-pressure and high-temperature conditions by raman spectroscopy indicates that at room temperature, the baddeleyite-type ZrO₂ begins to transform to a new phase at 3.4 GPa ,which identified as Pbca phase, and then Pbca phase transforms to a PbCl₂ phase. The formation of Pbca phase from baddeleyite phase doesn't need the...