SHORT RANGE ORDER IN ELEMENTAL LIQUIDS OF COLUMN IV

Stanislav Shor ² Martin Mayo ¹ Eyal Yahel ³ Guy Makov ²

¹Theory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge, Cambridge
²Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva
³Physics Department, Nuclear Research Center Negev, Beer-Sheva

Elemental Liquids of Col. IV are at the focus of intensive theoretical and
experimental studies for the last 20 years or so due to findings of liquid-liquid phase transitions (LLPT) and other anomalous physical properties such as increasing sound velocity with temperature or density anomalies. In this work, the short range order (SRO) in liquid elements Si, Ge, Sn, and Pb is analyzed using the quasi-crystalline model (QCM) applied to radial distribution functions (RDF’s), measured across a wide range of temperatures and pressures, considering a reference structure of A5 (β-Sn) symmetry with c/a ratios ranging from 0.3 to 1.0 compared with alternative structures such as SC, BCC, FCC and Diamond.
We report that l-Si, Ge and Sn are described with a β-Sn like SRO
whereas l-Pb with a bcc-like SRO. This implies the existence of strong directional bonding, the strongest in Si and decreasing in strength for Ge and Sn, which remain observable across a wide range of temperatures and pressures and disappearing in Pb, exhibiting a BCC-like SRO reflecting an absence of directional bonding.