Investigate On Stuctural And Electrical Properties Of PbMoO₄ Crystals And Dumbbell-Like ZnO Microcrystals At High Press

In this thesis, structural and electrical properties of PbMoO₄ and dumbbell-like ZnO microcrystals under high pressure have been studied by Raman spectroscopy, energy dispersed X-ray diffraction and electrical measurements. Pressure effects on the structure and the electrical transport behavior of the matter have been discussed.In-situ high-pressure Raman spectrum of PbMoO₄ shows that all Raman peaks disappears at 12.5 GPa, which indicates the PbMoO₄ sample would undergo an amorphous transition between 10.8GPa and 12.5GPa. Upon a decompression process from 26.5GPa to 9.4GPa, a very broad Raman peak still exists in low frequency region, however the peak at the wave number of 858 cm-1 can be re-found at 2.4GPa again, suggesting that the amorphous PbMoO₄ has recovered to crystalline phase.The results obtained from electrical conductivity measurements shows that the conductivity of PbMoO₄ increases with pressure and temperature increasing. However, the pressure effect on the electrical conductivity increase of PbMoO₄ is more obvious than temperature.On the other hand, structural and electrical properties of uniform dumbbell-like ZnO microcrystals have been also studied under high pressure. The sample was synthesized via a facile solution method under mild conditions. The dumbbell-like ZnO microcrystals, with lengths of 3.5-5.4μm and diameters of 1.3-1.8μm, has a single-crystal hexagonal structure and grow along the[0001] direction. High-pressure Raman scattering and X-ray diffraction were used to characterize the dumbbell-like ZnO, and we find that the dumbbell-like ZnO undergoes a phase transition from wurtzite phase to rock-salt phase in the pressure range of 9.1-11.3GPa. This phase transition is reversible, and has pressure sluggish phenomena. Besides, by using resistivity measurement on dumbbell-like ZnO microcrystals under high pressure we also find that the value of resistivity climbs with increasing pressure, and reaches its maximum value at 9.1GPa. With further increasing the pressure, the resistivity dramatically decreases until 11.2GPa, which indicates that ZnO microcrystals experiences a phase transition from wurtzite structure to rock-salt structure. We also measured the resistivity of samples which were annealed under various temperatures to illustrate the influence of oxygen vacancy on the sample resistivity. The impedance spectrum of dumbbell-like ZnO microcrystals shows two partially overlapped semicircles in the Nyqusit presentation, which represents grain boundary conduction and bulk conduction respectively. And the proportion of two arcs varies under various pressures, which attributes to pressure induced to sample resistivity changing. In conclusion, we uses high-pressure X-ray diffraction, Raman scattering, DC electrical conductivity, and AC impedance spectroscopy to detailedly investigate the structures and electrical properties of PbMoO₄ and dumbbell-like ZnO microcrystals under high pressure.