From first principles: Phase transition mechanisms of hexagonal Sc and Y under pressure

Using ab initio calculations, it is shown that the E2g mode and the elastic shear modulus C 44 for hexagonal Sc or Y begin to soften at almost the same pressure, which is about 20 GPa for hexagonal Sc and about 5 GPa for hexagonal Y. Their softening behavior might be induced by both electronic s→d transfer and p→d transfer, and may be responsible for the phase transitions of hexagonal Sc and Y metals under pressure.