High-pressure crystal structure of HgTe-IV

The crystal structure of HgTe-IV has been determined using angle-dispersive diffraction techniques, with synchrotron radiation and an image-plate area detector. The structure is not beta tin, as previously reported, but is found to be site ordered and orthorhombic with space group Cmcm. This is the same structure as has recently been found for CdTe-III/IV and ZnTe-III. However, HgTe exhibits a behavior different from either CdTe or ZnTe, in having a strongly first-order transition from a NaCl phase (HgTe-III) to Cmcm. The volume decrease at the transition is 1.2(1)%, and the Cmcm structure just above the transition is strongly distorted from NaCl. Two slightly different, but distinct, configurations of the structure give very similar fits to the diffraction data. Both configurations have significantly different coordination from CdTe-III/IV and ZnTe-III.