题目: Bonding, electronic and crystal structure of materials under extreme conditions
报告人: Dr. Wang Shibing
Geological and Environmental Sciences, Stanford University
SSRL, SLAC National Accelerator Laboratory
时间: 2011年10月10日 (星期一) ,上午 9:00
地点: 工艺楼406会议室
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Recent advances in high pressure diamond anvil cell techniques and synchrotron radiation characterization methods have enabled investigation of a wide range of materials properties in-situ under extreme conditions. High pressure studies have made significant contribution to our understanding in a number of scientific fields, e.g. condensed matter physics, chemistry, Earth and planetary sciences, and material sciences. Pressure, as a fundamental thermodynamic variable, can induce changes in the electronic and structural configuration of a material, which in turn can dramatically alter its properties. The novel phases and new compounds existing at high pressure have improved our basic understanding of bonding and interactions in condensed matter.
This talk surveys how pressure affects materials' bonding, electronic and crystal structures in two types of systems: hydrogen rich molecular compounds and strongly correlated transition metal compounds. The interaction of boranes and hydrogen was studied using optical microscopy and Raman spectroscopy and their hydrogen storage potential is discussed in the context of practical applications. The pressure-induced behavior of the SiH4 + H2 binary system and the formation of a newly formed compound SiH4(H2)2 were investigated using a combination of optical microscopy, Raman spectroscopy and x-ray diffraction. The experimental work along with DFT calculations on the electronic properties of the compound up to the possible metallization pressure, indicated that there are strong intermolecular interactions between SiH4 and H2 in the condensed phase. By using a newly developed synchrotron x-ray spectroscopy technique, we were able to follow the evolution of the 3d band of a 3d transition metal oxide, Fe2O3 under pressure, which experiences a series of structural, electronic and spin transitions at approximately 50 GPa. Together with theoretical calculations we revisited its electronic phase transition mechanism, and found that the electronic transitions are reflected in the pre-edge region. Finally, an on-going work on pressure-induced charge transfer of mixed valence compound CsAuI3, also a potential parent compound for high Tc superconductor, will be presented. Preliminary results from x-ray diffraction, Au L-edge x-ray near-edge absorption spectroscopy reveal strong electron-phonon coupling in the system.
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