| With the development of high pressure science, many new research areas are emerging. For materials science, high pressure technology provides various extreme conditions which are suitable for materials synthesis. Now, one of the main interests of materials scientists is developing new phases under high pressures and then quenching such phases to ambient conditions.In this dissertation, structure evaluations of hexagonal α-Ce3Al and PbTiO3are studied by using a two stage light gas gun and diamond anvil cells, respectively. X-ray diffraction, synchrotron radiation and high resolution TEM revealed the evidence of phase transitions of these materials. The mechanisms of such transitions were also studied.A series of shock compression experiments on hexagonal α-Ce3Al have been carried out using a two-stage light gas gun. No phase transition was observed in the recovered sample shock compressed at23.5GPa. However, as the shock pressure was increased to27.3GPa, a face-centered cubic Ce3Al phase was detected in the samples recovered at ambient conditions. Further, a Ce2Al phase was found in the37.1GPa shocked sample with a space group Fd-3m and lattice parameter a=8.26(1) A. These Ce-based alloys may have potential industrial applications due to heavy-fermion related properties.On the other hand, we carried out static high pressure experiments on tetragonal pre-provskite PbTiO3. Below10GPa, lattice parameters of pre-provskite PbTiO3decrease upon compression. However, above10GPa, c-axis of the lattice increase up to its maximum value at15.7GPa. During this process, the volume of the unit cell keeps almost the same. With the pressure continues to increase, although the structure could still be fitted by space group1/4m, the Bragg peaks of pre-provskite PbTiO3broaden significantly. Surprisingly, crystalline pre-provskite PbTiO3will gradually transform to amorphous when decompressed from high pressure. This may be caused by the development of defects and disorders during decompression process. |
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