Phase transitions in CdTe to 28 GPa

Angle-dispersive powder-diffraction techniques utilizing an image-plate area detector and synchrotron radiation have been used to study the phase transitions in CdTe above 8 GPa. The well-known phase transition at 10 GPa is not to the β-tin structure as has previously been reported, but to an orthorhombic structure with space group Cmcm. This is the same structure as recently reported for ZnTe-III, and is characterized by a fivefold coordination of close nearest neighbors. The Cmcm phase is stable to at least 28 GPa, and the pressure dependence of the structure has been determined over this range. The continuous nature of the NaCl→Cmcm transition, coupled with the limited resolution and lower sensitivity of previous studies, accounts for the earlier reports of a β-tin phase, and of a transition at 12 GPa from the supposed β-tin phase to an orthorhombic phase with space group Pmm2.