Vacancy Formation Energies in Close-Packed Crystals Correlated with Melting Temperature Via Thermodynamics and Liquid Structure.

摘要

In earlier work, the vacancy formation energy E/sub v/ in close-packed crystals, in units of the thermal energy k/sub B/T/sub m/ at the melting temperature T/sub m/, has been connected with compressibility and specific heats, plus terms dependent on the liquid structure at T/sub m/. Here, this connection has been examined quantitatively for (a) the insulating condensed rare gases Ne, Ar and Kr, and (b) a variety of close-packed metals. For case (a), E/sub v//k/sub B/T/sub m/ can be calculated directly from thermodynamic data to obtain agreement with experiment for Ar and Kr, though not for Ne. A 'residual' contribution is estimated for Ar and Kr from diffraction and computer experiments on the density dependence of the liquid pair correlation function and is shown to be very small. Agreement is less impressive for case (b) for the eight close-packed metals for which all data required is known, the thermodynamic formula giving an average value E/sub v//k/sub B/T/sub m/=7.8+-1.1 whereas experiment yields 9.4+-1.8. However, for the body-centred cubic alkalis the thermodynamic average value of 4.5+-0.5 is much lower than the experimental value 11.5+-2.0 consistent with the known role of ionic relaxation round the vacancy in such open structures. (author). 16 refs, 2 tabs. (Atomindex citation 19:102086)