Searching for Stable Beryllium Carbonates in the BeO–CO₂ System

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 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.