High Pressure Synchrotron Radiation X-Ray Diffraction Study On Typical Oxygen Group Metal Compounds Nanomaterials

As a kind of excellent semiconductor, oxygen group metal compound, which shows good electrical and optical properties, has becoming an important research object in nano-materials and condensed matter science recently. High-pressure researches on Oxygen group metal compound nano-materials has become a hot spots in the field of high-pressure studies and has significant scientific implications. In this paper, three kinds of representative oxygen group metal compounds, lead sulfide, zinc selenide and silver sulfide, were chosen for synchrotron radiation X-ray diffraction experiment to study the morphology, exposed surfaces, size influences to high-pressure character.PbS nanocrystals with regular cubic shape and octahedral shape were investigated by in-situ high-pressure synchrotron X-ray diffraction method for the first time. High-pressure property of both samples were studied to characterize the difference between nano-crystal sample and bulk material, or difference between samples with different morphology. It was found that, both cubic and octahedron samples undergo a series of pressure-induced first-order structural phase transition fromα-PbS phase toβ-PbS and finally toγ-PbS phase. The onset phase transition pressure of both samples is 3.6GPa, higher than bulk material and lower than other nanoparticle PbS. The second critical phase transition pressure is 25GPa. Through the fitting of Birch-Murnaghan equation of state, we could make a conclusion that bulk modulus of octahedral PbS withα-PbS phase is at least 16.4% large than cubic samples, after phase transition toβ-PbS and finally toγ-PbS, bulk modulus of cubic sample are twice about octahedral sample. Studies of several possible factors which affect the bulk modulus shows the bulk modulus difference in low pressure area is caused by different exposure crystal surface. Theoretical simulation of crystal surface energy was carried out, during the compress process, surface engery of (111) increase faster than (100). This is consistent with our experiment. This provides us a new possibility to modify the physical property of the nanomaterial via controlling the surface of the nanocrystal.Zinc selenide nanoparticles (~6nm) were studied by high-pressure synchrotron radiation X-ray diffraction for the first time. Phase transition behaviors were investigated, and found that ZnSe sample undergoes a pressure-induced first-order structural phase transition from ZB phase to RS phase at about 17.2GPa. The onset pressure of phase transition is 4GPa higher than bulk material, and the appearance of phase which was found in bulk material was not observed. Fitting results of equation-of-status shows the bulk modulus of ZB phase and RS phase are 103.9GPa and 89.5GPa. In the low pressure area, bulk modulus of ZB phase ZnSe nanoparticles is larger than that of bulk material.Hexagonal silver sulfide nano-sheets (~20 nm) were investigated by high-pressure synchrotron radiation X-ray diffraction. It is found for the first time that silver sulfide nano-sheet began to transform into amorphous at 16.5GPa, and during down stroke process the nano-sheet recovered its crystallization.