1. Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China 2. Institute of High Energy Physics,Chinese Academy of Sciences,Beijing 100049,China 3. Institute of Geochemistry,Chinese Academy of Sciences,Guiyang 550002,China
Abstract：The pressure-induced phase transition of rutile-structured TiO2 was investigated by in-situ Raman spectrum method in a laser-heated diamond anvil cell (DAC). The experiment was conducted at 35 GPa under quasihydrostatic conditions using argon as medium. At room temperature,the rutile-type TiO2 begins to transform to baddeleyite-type phase at 13.4 GPa and completes at 21 GPa,and this new high-pressure structure retains up to 35 GPa,the upmost pressure used in this study. At the pressure of 29.4 GPa the sample of baddeleyite-type TiO2 was heated by an YAG laser to about 1 000-1500 ℃,and then the baddeleyite phase transformed to a Pbca phase. The Pbca phase was heated again at 35.0 GPa and it was still stable. The sample then began to be decompressed,and the Pbca phase of TiO2 transformed to baddeleyite structure at 26.3 GPa,which stayed stable to 11.4 GPa. 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 that on its formation,which suggests the boundary of the two phases can be determined at about 28 GPa. At 7.6 GPa,and the Raman spectrum shows the characteristics of the mixture of two phases of baddeleyite-type and α-PbO2-type,which indicates that the baddeleyite phase transforms to α-PbO2 phase at about 7 GPa. The α-PbO2-type TiO2 is metastable under ambient condition.
Key words：Rutile;High-pressure and high-temperature phase transformations;Raman spectra;Baddeleyite phase;Pbca phase;α-PbO2 phase
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