Abnormal behavior of Cs polyoxides under high pressure

TL;DR

This study reveals that high pressure induces a unique chemical transition in Cs polyoxides, activating core electrons and leading to novel bonding structures unlike typical polyoxides, with potential for experimental validation.

Contribution

It demonstrates how high pressure activates Cs 5p core electrons, causing unprecedented structural and chemical changes in Cs polyoxides, especially CsO, under extreme conditions.

Findings

Cs polyoxides undergo a chemical transition at 221 GPa.

O-O bonds disappear, forming Cs-O covalent bonds.

CsO remains stable as a peroxide under high pressure.

Abstract

High-pressure can transform the structures and compositions of materials either by changing the relative strengths of bonds or by altering the oxidation states of atoms. Both effects cause unconventional compositions in novel compounds that have been synthesized or predicted in large numbers in the past decade. What naturally follows is a question: what if pressure imposes strong effects on both chemical bonds and atomic orbitals in the same material. A systematic DFT and crystal structure search study of Cs polyoxides under high pressure shows a striking transition of chemistry due to the activation of the Cs 5p core electrons. Opposing to the general trend of polyoxides, the O-O bonds disappear in Cs polyoxides and Cs and O atoms form molecules and monolayers with strong Cs-O covalent bonds. Especially, the abnormal transition of structure and chemical bonds happens to CsO, a solid peroxide that is stable under ambient pressure, at 221 GPa, which can be accessed by current high-pressure experiments.