期刊
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS
卷 69, 期 8, 页码 1912-1922出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jpcs.2008.01.019
关键词
high pressure; equations of state; phase equilibria; thermal expansion; thermodynamic properties
Semi-empirical equations of state (EOS) are used for interpolation and extrapolation of experimental data and/or electronic structure calculations. For calculation of phase equilibria, it is preferable to use an explicit Gibbs free energy EOS, that is, to express the Gibbs free energy directly as a function of the pressure and temperature. Existing explicit Gibbs free energy EOS formulations often give unphysical predictions at high pressures. The origins of these problems are internal inconsistencies and uncontrolled extrapolations. A set of conditions is put forward, that should be fulfilled by semi-empirical EOS formulations in order to constrain them to known physical behaviour, e.g., to the Thomas-Fermi and quasi-harmonic models at high pressures. A new alternative integration path is devised that eliminates the need for the problematic extrapolation of the heat capacity to high temperatures at low pressures. Based on these developments, a new explicit Gibbs free energy EOS is formulated which is suitable for computational applications. The new EOS may be fitted to represent the thermophysical properties of solids with a reasonably small number of adjustable parameters. A sample application for MgO is presented. (C) 2008 Elsevier Ltd. All rights reserved.
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