Phosphorous dimerization in GaP at high pressure

TL;DR

This study reveals that gallium phosphide adopts a new high-pressure phase with phosphorous dimerization at 43 GPa, combining experimental and computational methods to understand its structure and stability.

Contribution

It introduces the super-Cmcm (oS24) structure of GaP at high pressure, highlighting phosphorous dimerization and its implications for high-pressure polymorphism in semiconductors.

Findings

GaP adopts super-Cmcm structure at 43 GPa and 1300 K

oS24 structure is more stable than other polymorphs above 20 GPa

Phosphorous dimerization occurs in high-pressure GaP

Abstract

Using combined experimental and computational approaches we show that at 43 GPa and 1300 K gallium phosphide adopts the super-Cmcm structure, here indicated with its Pearson notation oS24. First-principles enthalpy calculations demonstrate that this oS24 structure is more thermodynamically stable above about 20 GPa than other proposed polymorphs, such as cubic ZB and SC16 or the ubiquitous orthorhombic Cmcm phase (oS8). It is found that oS24-structured GaP exhibits short P-P bonds, according to our high-resolution structural analysis. Such phosphorous dimerization in GaP, observed for the first time and confirmed by ab initio calculations, sheds light on the nature of the super-Cmcm structure and provides critical new insights into the high-pressure polymorphism of octet semiconductors. Bond directionality and anisotropy, in addition to 5-fold phosphorous coordination, explain the relatively low symmetry of this high-pressure structure.