Searching for Stable Beryllium Carbonates in the BeO–CO2 System

Abstract

In this work, the BeO–CO₂ system was investigated in the pressure range from 0 to 50 GPa based on first-principles calculations and modern crystal structure prediction approaches. As a result, one stable compound with intermediate stoichiometry BeCO₃ was predicted at all considered pressure ranges, while a near-ground-state compound Be₂CO₄ decomposed into two neighboring compounds under compression. For BeCO₃, the structure Ama2, two enantiomorphic phases P3₁21 and P3₂21, and the modification R3̅c were predicted to be stable. According to the obtained results, the following sequence of polymorphic transitions : 𝐴𝑚𝑎2→𝑃3121→𝑅3¯𝑐$Ama2\to P{3}_{1}21\to R\overline{3}c$$Ama2\to P{3}_{1}21\to R\overline{3}c$ at 4.5 and 36 GPa at low temperatures, respectively. The high-pressure modification R3̅c retains its stability at least up to 50 GPa without decomposition or polymorphic transition. The Ama2 and P3₁21 modifications are characterized by the presence of chains of [BeO₄] tetrahedra shared with [CO₃] triangles, whereas the high-pressure modification R3̅c belongs to the calcite structural type, and the [BeO₄] tetrahedra are replaced by [BeO₆] octahedra. Beryllium carbonate in the Ama2 and P3₁21 structures can be recovered at atmospheric pressure. In addition, the electronic density of state and band structures of all predicted modifications of BeCO₃ were calculated.