PHASE-TRANSFORMATION OF BESE AND BETE TO THE NIAS STRUCTURE AT HIGH-PRESSURE

We report the existence of a reversible pressure-induced first-order p hase transition between the zincblende (B3) and the NiAs (B8) phase in the beryllium chalcogenides BeSe and BeTe at pressures of 56+/-5 GPa and 35+/-5 GPa, respectively. The NiAs phase remains stable in both co mpounds with further pressure increase up to at least 72 GPa in BeSe a nd 53 GPa in BeTe. For BeTe, an amorphous phase was observed upon deco mpression in the pressure range from 47 to 32 GPa. The equation of sta te is determined for each compound. We discuss the systematic trends o f the structural phase transition, the stability of the NiAs structure , amorphization, as well as metallization in the beryllium chalcogenid es.