Helium ordered trapping in arsenolite under compression: Synthesis of He2As4O6

TL;DR

This study combines experimental and theoretical methods to demonstrate helium trapping in arsenolite under high pressure, leading to a new stable compound that resists amorphization and alters the material's properties.

Contribution

It provides the first evidence of helium trapping in arsenolite, resulting in a novel compound with enhanced stability and modified properties under pressure.

Findings

Helium is trapped between arsenolite cages above 3 GPa.

Helium trapping prevents pressure-induced amorphization.

The new compound He2As4O6 remains stable beyond 30 GPa.

Abstract

The compression of arsenolite (cubic As2O3) has been studied from a joint experimental and theoretical point of view. Experimental X-ray diffraction and Raman scattering measurements of this molecular solid at high pressures with different pressure-transmitting media have been interpreted with the help of ab initio calculations. Our results confirm arsenolite as one of the softest minerals in absence of hydrogen bonding and provide evidence for helium trapping above 3 GPa between adamantane-type As4O6 cages, thus leading to a new compound with stoichiometry He2As4O6. Helium trapping alters all properties of arsenolite. In particular, pressure-induced amorphization, which occurs in pure arsenolite above 15 GPa, is impeded when He is trapped between the As4O6 cages; thus resulting in a mechanical stability of He2As4O6 beyond 30 GPa. Our work paves the way for the modification of the properties of other molecular solids by compression depending on their ability to trap relatively small atomic or molecular species and form new compounds. Furthermore, our work suggests that compression of molecular solids with noble gases as helium could result in unexpected results compared to other pressure-transmitting media.