Invited
STRUCTURE AND PHASE TRANSITIONS OF SIMPLE LIQUIDS AND GLASSES UNDER PRESSURE PROBED BY X-RAY ABSORPTION SPECTROSCOPY

The structure of liquids and glasses at extreme conditions of pressure and temperature has been the subject of a considerable amount of both theoretical and experimental work. Within the available experimental techniques, X-ray absorption spectroscopy (XAS) has the capability to provide precise atom specific information on the average distribution of the nearest neighbours, and beyond the pair correlations when combined with suitable data analysis strategies.

In our previous studies, Reverse Monte Carlo (RMC) modelling of XAS data [1] has been applied to provide a deep insight into the atomic correlations at the microscopic level and address important issues, such as the presence and extent of local icosahedral ordering in liquid close-packed metals [2,3]. We have recently extended the application of RMC-XAS [1] to multiatomic substances, such as gas-phase molecular systems, metallic alloys, and chalcogenide glasses. Multiple-edge XAS analysis using RMC methods, combined with other structural data like diffraction, is shown to provide a reliable tool for the reconstruction of the local geometry in disordered matter around selected atomic species. Structural models, compatible with available experimental data, are used to obtain detailed statistical analysis of local coordination, chemical disorder and geometry, shedding light on the structural transformations occurring under variable pressure and temperatures.

[1] A. Di Cicco, A. Trapananti, J. Phys. Condens. Matter 2005, 17, S135.

[2] A. Di Cicco, A. Trapananti, S. Faggioni, A. Filipponi Phys. Rev. Lett. 2003, 91,135505.

[3] A. Di Cicco, F. Iesari, S. De Panfilis, M. Celino, S. Giusepponi, A. Filipponi Phys. Rev. B 2014, 89, 060102.