Low-symmetry polymorph of GaP upends bonding paradigms of metallic high-pressure III-V compounds

TL;DR

This study reveals that the high-pressure phase of GaP is an ordered monoclinic structure, challenging previous assumptions of disorder and suggesting a need to re-examine bonding paradigms in high-pressure III-V compounds.

Contribution

It uncovers a previously unknown ordered monoclinic structure in GaP's high-pressure phase, overturning prior notions of disorder and expanding understanding of high-pressure polymorphism.

Findings

GaP's high-pressure phase II is ordered, not disordered.

Layered patterns with variable interlayer dimerization are observed.

The discovery prompts a re-evaluation of bonding in high-pressure III-V compounds.

Abstract

The pressure-induced polymorphism of binary octect compounds has long been considered a settled problem although the possible atomic disordering of some phases remains a puzzling observation. Taking GaP as a case study, we conclude, through x-ray microdiffraction and first-principles calculations, that its high-pressure phase II (previously reported as being disordered) adopts in fact an ordered base-centered monoclinic structure previously unknown in this class of compounds. The formation of layered patterns with variable degrees of interlayer dimerization, as observed in GaP, marks a paradigm shift of our understanding of ordering in octect high-pressure phases which calls for a more extensive re-examination. A rich polymorphism with fine tuning of chemical and physical properties can be envisioned.