Crystal structures and P–T phase diagrams of SrC2O5 and BaC2O5

Abstract

AbstractIn this study, we present the results of a search for new stable structures of SrCO and BaCO in the pressure range of 0–100 GPa based on the density functional theory and crystal structure prediction approaches. We have shown that the recently synthesized pyrocarbonate structure SrCO‐ is thermodynamically stable for both SrCO and BaCO. Thus, SrCO‐ is stable relative to decomposition reaction above 10 GPa, while the lower‐pressure stability limit for BaCO‐ is 5 GPa, which is the lowest value for the formation of pyrocarbonates. For SrCO, the following polymorphic transitions were found with increasing pressure: at 40 GPa and 1000 K, at 90 GPa and 1000 K. SrCO‐ and SrCO‐ are characterized by the framework and layered structures of [CO] tetrahedra, respectively. For BaCO, with increasing pressure, decomposition of BaCO‐ into BaCO and CO is observed at 34 GPa without any polymorphic transitions.