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High-pressure behavior of GaP has been studied by x-ray-absorption spectroscopy in a diamondanvil cell up to 36 GPa. The room-temperature equation of state of phase I has been determined.The transition from a fourfold (zinc-blende) to a sixfold (P-tin) coordination scheme is observed near 26 GPa. Analysis of the data obtained on a sample quickly depressurized from 36 GPa shows that the transition is not reversible and the recovered sample is mainly amorphous.

The authors have measured the dependence of the absorption coefficient on quasi hydrostatic pressure in GaP up to 23.3 GPa in the region of the indirect gap energy (Eg) at room temperature. They have found a linear behaviour of Eg with pressure up to 17 GPa with a pressure coefficient of -14.9+or-0.5 meV GPa-1. Transmission measurements, electronic diffraction, X-ray diffraction, Raman scattering and photographs under microscope have been used to characterise the phase transition. It begins between 21 and 22 GPa. The transited phase, after depressurisation from 32 GPa, contains a mixture of polycrystalline and amorphous GaP.

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