Thermal properties of iron at high pressures and temperatures

Abstract

We investigate the thermoelastic properties of close-packed phases of iron at pressures up to 400 GPa and temperature to 6000 K using a tight-binding total-energy method and the cell model of the vibrational partition function. The calculated properties are in good agreement with available static and shock-wave experimental measurements. The compressional behavior of a number of thermoelastic parameters is found to resemble that of a prototypical oxide (MgO) supporting some aspects of universal behavior at high compression: the product of thermal expansivity \ensuremath{\alpha} and bulk modulus is found to be nearly independent of compression at high pressure and the logarithmic volume derivative of \ensuremath{\alpha} is found to decrease with compression. In contrast to the behavior of MgO, \ensuremath{\alpha}${\mathit{K}}_{\mathit{T}}$ and ${\mathrm{\ensuremath{\delta}}}_{\mathit{T}}$ of iron are found to depend strongly on temperature due to contributions from the thermal excitation of electrons. Significant decrease of the elastic constants of hcp iron with temperature was found. \textcopyright{} 1996 The American Physical Society.