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A combination of x-ray-diffraction measurements, using a diamond-anvil cell, and electrical-resistance measurements, employing an octahedral-anvil press, has been used to elucidate the behavior of GeSe and GeTe at high pressure. In GeSe, x-ray data show that the array of six-membered rings in chair conformation along the a direction is the most compressible. The electrical resistivity decreases with increasing pressure and exhibits an order of magnitude drop at about 25 GPa. GeTe transforms from the rhombohedral to the NaCl-type structure at 3 GPa and, at 18 GPa, transforms into a possibly orthorhombic structure with a space group Pbcn, accompanied by a remarkable rise in electrical resistivity. General trends in the pressure-induced structural phase transitions of group-IV and group-VI compounds are discussed in terms of ionicity and covalency.
Onodera et al. (Wed,) studied this question.