Thermoelectric properties of GeTe at high hydrostatic pressure up to 8.5 GPa and its valence‐band structure

The thermopower and the relative electrical resistance of rhombohedral α‐GeTe and orthorhombic γ‐GeTe polycrystalline samples with hole density between 3.9 × 10 20 and 2 × 10 21 cm −3 are measured under hydrostatic pressure up to 8.5 GPa at room temperature. The phase transition of α‐GeTe to the cubic rocksalt structure (β‐GeTe) reported earlier at 3.5 GPa under nonhydrostatic pressure is not observed up to 8.5 GPa. Orthorhombic γ‐GeTe also exhibits no phase transition. The pressure dependences of the thermopower provide support for the multiple valence‐band model of GeTe.