Seminar 19 March 2015: Local ordering in liquid metals probed by x-­ray absorption spectroscopy by F. Iesari

Local ordering in liquid metals probed by x­-ray absorption spectroscopy

F. Iesari, A. Di  Cicco, S. De Panfilis, A. Filipponi

The nature of local point symmetry in simple monoatomic liquids has been a fundamental open question for almost 40 years of computational and experimental studies, following Frank’s initial hypothesis about the presence of icosahedral short­range ordering (ISRO) in liquids. In recent decades, several computational and experimental studies were devoted to investigating locally preferred structures in simple atomic liquids and most of these works support the existence and importance of ISRO. We have performed an extensive investigation on liquid and undercooled liquid metals, combining state­of­the­art x­ray absorption spectroscopy (XAS) and computational techniques (Reverse Monte Carlo), for the purpose of evaluating the amount of ISRO, using reliable criteria for assessing the nature of local geometries in liquids (common-neighbor analysis, spherical invariants). We present original results of typical closed­-packed metals (Cu, Ni) where the presence of ISRO is 10­-14% embedded in a disordered network mainly composed of fragments of highly distorted icosahedra. New preliminary results of Cd and Zn are also presented, where ISRO is still present, but qualitative differences in the bond­-angle distribution can be appreciated, showing a slight difference local ordering respect to the close-packed case.

The seminar will be held in room H (Tchoudinov), Physics Division, 15:00 PM 19 March 2015