Anharmonicity in thermal pressure for aluminium

Abstract

An expression for the volume dependence of thermal pressure is formulated using basic thermodynamic identities. It is applied to aluminium metal for which sufficiently reliable data are available for comparison. The calculations are performed using the two models viz. the Thomas-Fermi model and the Stacey-Davis model. It is found that the values of thermal pressure for <i style="mso-bidi-font-style: normal">m</i>=6 in both models are almost the same. Thermal pressure increases with the increase in pressure. The anhormonic effects are found to be dominant below about (<i style="mso-bidi-font-style:normal">P</i>=60 GPa). While above this, harmonic effects become dominant. The anharmonic effects are very important at low pressures and become less significant as the pressure is increased. Values of thermal pressure have been calculated by taking into account the effect of the change in volume on melting. The results obtained for aluminium indicate that the present model is capable of predicting the volume dependence of thermal pressure, which is found to be in good agreement with the available data for a wide range of pressures and temperatures