Thermal properties of iron at high pressures and temperatures

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 α and bulk modulus is found to be nearly independent of compression at high pressure and the logarithmic volume derivative of α is found to decrease with compression. In contrast to the behavior of MgO, α${\mathit{K}}_{\mathit{T}}$ and ${\mathrm{\delta }}_{\mathit{T}}$ 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. © 1996 The American Physical Society.