Searching for Stable\nBeryllium Carbonates in the BeO–CO<sub>2</sub> System

In\nthis work, the BeO–CO<sub>2</sub> system was\ninvestigated\nin the pressure range from 0 to 50 GPa based on first-principles calculations\nand modern crystal structure prediction approaches. As a result, one\nstable compound with intermediate stoichiometry BeCO<sub>3</sub> was\npredicted at all considered pressure ranges, while a near-ground-state\ncompound Be<sub>2</sub>CO<sub>4</sub> decomposed into two neighboring\ncompounds under compression. For BeCO<sub>3</sub>, the structure <i>Ama</i>2, two enantiomorphic phases <i>P</i>3<sub>1</sub>21 and <i>P</i>3<sub>2</sub>21, and the modification <i>R</i>3̅<i>c</i> were predicted to be stable.\nAccording to the obtained results, the following sequence of polymorphic\ntransitions : Ama2→P3121→R3̅c at 4.5 and 36 GPa at low temperatures,\nrespectively. The high-pressure modification <i>R</i>3̅<i>c</i> retains its stability at least up to 50 GPa without decomposition\nor polymorphic transition. The <i>Ama</i>2 and <i>P</i>3<sub>1</sub>21 modifications are characterized by the presence of\nchains of [BeO<sub>4</sub>] tetrahedra shared with [CO<sub>3</sub>] triangles, whereas the high-pressure modification <i>R</i>3̅<i>c</i> belongs to the calcite structural type,\nand the [BeO<sub>4</sub>] tetrahedra are replaced by [BeO<sub>6</sub>] octahedra. Beryllium carbonate in the <i>Ama</i>2 and <i>P</i>3<sub>1</sub>21 structures can be recovered at atmospheric\npressure. In addition, the electronic density of state and band structures\nof all predicted modifications of BeCO<sub>3</sub> were calculated.