HIDDEN HIGH-TO-LOW CRISTOBALITE TYPE TRANSITION IN HGSE AND HGTE AT HIGH-PRESSURE

A transition from the zinc blende (ZB) phase to a distorted-ZB structu re has been found in both HgSe and HgTe. This is a structure type not previously reported in any of the II-VI or III-V systems. The transiti on occurs similar to 1 GPa above the pressure at which the ZB phase be comes unstable against the cinnabar phase, and is thus observable only because of the sluggishness of the ZB to cinnabar transformation. The atomic coordinates of the distorted-ZB structure are remarkably simil ar to those of the cations in the low-cristobalite phases of AlPO4 and GaPO4.