Raman Study Of The Phase Transformations Of TiO₂ Under Static High-Pressure

The new characters of material which is not found at ambient pressure can be found at high-pressure, then the researchs reveal new characters ,new quality and even discover new materials, it is the new way to research the characters of material at ambient pressure and explain the phenomenon at ambient pressure.In-situ high pressure Raman spectroscopyplays an important role for understanding not only the fundamental physical properties of condensed matter, but also the physical and chemical processes in the Earth's dynamic interior. Detailed information on the variety of phonon spectra, electron-phonon interaction and the anharmonic effect on lattice vibration at pressure could be obtained from the Raman spectra recorded under HP condition. Furthermore , phase transitions are researched by high-pressure Raman spectroscopy.In this thesis, single crystal of rutile and powder anatase TiO₂ were studied by Raman spectroscopy at quasi-hydristatic pressures using diamond anvil cell(DAC) at room temperature. The emphases of the research are Raman spectroscopy at room temperature and ambient pressure and at room temperature and high-pressure. At the same time, we studied the law which two character peaks moved and changed with increasing pressure before the phase transition of single crystal of rutile at room temperature. In contrast to phase transition in other references, we find the law of phase transition of two sample and provide experiment data which revealed the law of phase transition of two samples .一,Experimental detailsThe single crystal of rutile was grown by Floating Zone method by teacher Guo in this experimental.The powder anatase TiO₂ was bought from the frist reagent factory of ShenYang. T301 stainless steel of thickness 0.25mm was used for gasketing. After preindention to 50-60μm in thickness, a 140-200μm diameter hole was drilled at the center of the indented region. A 4:1 mixture of methanol and ethanol was used as the pressure-transmitting medium. The pressure of the diamond-anvil cell was determined from the shift of the ruby fluorescence line.二,The main conclusions(1) Single crystal of rutile TiO₂ begins to transform into baddeleyite structure(MI) at about 12.91GPa, the phase transition is finished at about 14.16GPa. Because the Raman spectroscopy contained almost all the peaks of baddeleyite structure(MI),we conclude that the sample is not single crystal in this time, it is polycrystal. We did not find the next phase transition until about 21.65 GPa for the other same sample. On decompression at about 7.11 GPa the baddeleyite structure(MI) transforms intoα-PbO2 structure(TiO₂â…¡). This process and press of phase transition are different from the experiment conclusion of H.Arashi. For this difference, we can consider the reason of experiment sample and experiment technique. Although these are all single-crystal sample, the preparation method and the integrality of structure of single-crystal are not certain same, and grain size is not same. Although the pressure was all determined from the shift of the ruby fluorescence line, because of experiment instrument, it is impossible that there is difference of 0.5GPa. (2) We studied the law which two character peaks moved and changed with increasing pressure before the phase transition of single crystal of rutile at room temperature. With increasing pressure, two character peaks move to high wavenumber in line and the speed of moving of 613.87 wavenumber(Eg) is larger than 451.22 wavenumber(A1g). The speed of moving is 3.284cm^-1 /GPa and 3.389cm^-1 /GPa. With increasing pressure, the relatively intensity of two character peaks is changed too.The relatively intensity of 613.87 wavenumber(Eg) is more weak than 451.22 wavenumber(A1g).When approach phase transition pressure, the speed of moving of two peaks is changed; after phase transition beginning the speed of moving of two peaks is diffirent obviously from the speed before phase transition beginning, so this proved that the structure of sample changed indirectly.(3) Powder anatase TiO₂ begins to transform intoα?PbO2 structure(TiO₂â…¡) at about 4.26GPa, the phase transition is finished at about 8.34GPa. The phase transition is irreversible.α-PbO2 structure ( TiO₂â…¡) begins to transform into baddeleyite structure(MI) at about 12.94GPa, the phase transition is finished at about 18.74GPa. We did not find the next phase transition until about 21.39 GPa. On decompression at about 7.94 GPa the baddeleyite structure(MI) transforms intoα-PbO2 structure(TiO₂â…¡).The conclusion is the same of references, the only difference is the pressure point of phase transition that is happened in the decompression process. After the analyse, we consider that pressure point 7 GPa of phase transition in the decompression process is an average.But in truth ,phase transition is happened in pressure region. So it is impossible that there is difference of phase transition point in reference. Our data is more exact.