Toward Analysis of Structural Changes Common for Alkaline Carbonates and Binary Compounds: Prediction of High-Pressure Structures of Li₂CO₃, Na₂CO₃, and K₂CO₃

The behavior of alkaline carbonates at high pressure is poorly understood. Indeed, theoretical and experimental investigations of the pressure induced structural changes have appeared in the literature only sporadically. In this article we use evolutionary crystal structure prediction algorithms based on density functional theory to determine crystal structures of high-pressure phases of Li₂CO₃, Na₂CO₃, and K₂CO₃. Our calculations reveal several new structures for each compound in the pressure range of 0–100 GPa. Cation arrays of all high-pressure structures are of the AlB₂ topological type. The comparison of cation arrays of ambient and high-pressure structures with that of binary A₂B compounds indicates an analogy between high-pressure behavior of alkaline carbonates and alkaline sulfides (oxides, selenides, tellurides), which under compression go through the following series of phase transitions: anti-CaF₂ → anti-PbCl₂ → Ni₂In → AlB₂. All structures presented in this trend are realized in the high-pressure trend of alkaline carbonates, although some intermediary structures are omitted for particular compounds