Thermodynamics of uniaxial phase transition: Ab initio study of the diamond-to-β-tin transition in Si and Ge
The diamond-to-β-tin phase transitions of Si and Ge under uniaxial compression are investigated with ab initio calculations. A thermodynamic analysis is used to identify the transition pressures at uniaxial compression. The transition pressures were found to be pronouncedly lower than those at hydrostatic compression, i.e., 3.9 and 2.5 GPa compared to 11.4 and 9.5 GPa for Si and Ge, respectively. The different contributions to the phase transition are analyzed numerically and discussed.