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»ã±¨±êÌâ(Ó¢ÎÄ)£ºZEOLITES, AMORPHISATION and PERFECT GLASSES

»ã±¨ÄÚÈݼò½é£ºUnder pressure, crystals transform into amorphous structures well below the melting point Tm. The amorphisation of zeolite crystals is particularly interesting, as this can also be achieved at ambient pressure by employing only modest temperatures. Different thermobaric stress rates reveal the dynamics of microporous collapse as well as the existence of a supercooled intermediate. This is topologically equivalent to the zeolitic precursor, but also extremely strong – approximately twice as strong as silica, usually considered the strongest glass-forming liquid. A low entropy or “perfect glass” is formed on depressurising or cooling, whose mechanical properties are distinct from a glass conventionally quenched from the molten state. Both types of glass are polymorphs and the amorphisation process can be envisaged as a pair of first order phase transitions: crystal-liquid and liquid-liquid (Greaves et al, Nature Materials, 2, 622-629 (2003); Science 308, 1299 (2005)). The talk will introduce these ideas and also report recent work on the amorphisation of zeolitic imidazolate frameworks (ZIFs). Like inorganic zeolites the structural relaxation times of amorphising hybrid ZIFs extend over several minutes, comparable to time scales encountered at the glass transition Tg, and uncovering the existence of novel organic-inorganic supercooled liquids.

»ã±¨ÈËÐÕÃû£ºG.N. Greaves
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»ã±¨È˼ò½é(Ó¢ÎÄ)£ºSenior Research Professor of University of Alberta UK. Professor Greaves is well-known for his substantial contributions to disordered materials, particularly glass and amorphous solids. He is the authority of the British synchrotron radiation materials science and pioneered the development of X-ray absorption fine structure spectroscopy techniques in 1980s. He was the first material scientist to study glass material using X-ray scattering of synchrotron light sources and Spectroscopic Studies, and achieving a breakthrough and original results about how to "observe" these materials. Especially his "improved random frame" model, although in the early proposed, controversial, has now become the most important research silicate glass reference. Recently, he became the main leaders in the development and application of online research in oxide high-temperature molten salt structure and dynamics using X-ray and neutron scattering techniques. He has published a number of related papers in the liquid and glass . "multi-amorphous" aspect of this important phenomenon has attracted a large number of great interest not only in the oxide material and glass materials from the academic field, and even in theoretical chemistry and condensed matter physics scientist. It is very prominent and cutting-edge new research directions in low-density crystals "amorphous" caused by hypertension and phase transformation kinetics of solid state physics . Greaves has won the "Shanghai Overseas teacher" and the Shanghai Municipal Bureau of Foreign Experts "high-end foreign experts" project support at Shanghai University, cooperation and communication.

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»ã±¨È˵¥Ôª(Ó¢ÎÄ)£ºInstitute of Mathematics, Physics and Computer Sciences, Aberystwyth University, UK Department of Materials Science & Metallurgy, University of Cambridge

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