Abstract
Phase equilibria of materials at high pressures and high temperatures are determined by high-pressure and high-temperature experiments, and also by thermodynamic calculation with calorimetric data. The thermodynamic calculation is very useful to examine whether the experimentally determined phase relations are in equilibrium with sufficient accuracy, and to determine the equilibrium phase boundary at pressure-temperaure conditions where equilibrium is difficult to attain in high-pressure experiments. The issues are illustrated in coesite-stishovite transition and rutile-αPbO2 transition in TiO2. Calculated boundaries of postspinel transition in Mg2SiO4 are shown to compare with experimentally determined boundaries along with evaluating effect of cation-disorder in spinel on the boundary slope.
