Sr<sub>3</sub>[CO<sub>4</sub>]O Antiperovskite with Tetrahedrally Coordinated sp<sup>3</sup>-Hybridized Carbon and OSr<sub>6</sub> Octahedra
Dominik Spahr, Jannes König, Lkhamsuren Bayarjargal, Pavel N. Gavryushkin, Victor Milman, Hanns‐Peter Liermann, Björn Winkler
Abstract
We have synthesized the orthocarbonate Sr3[CO4]O in a laser-heated diamond anvil cell at 20 and 30 GPa by heating to ≈3000 (300) K. Afterward, we recovered the orthocarbonate with [CO4]4– groups at ambient conditions. Single-crystal diffraction shows the presence of [CO4]4– groups, i.e., sp3-hybridized carbon tetrahedrally coordinated by covalently bound oxygen atoms. The [CO4]4– tetrahedra are located in a cage formed by corner-sharing OSr6 octahedra, i.e., octahedra with oxygen as a central ion, forming an antiperovskite-type structure. At high pressures, the octahedra are nearly ideal and slightly rotated. The high-pressure phase is tetragonal (I4/mcm). Upon pressure release, there is a phase transition with a symmetry lowering to an orthorhombic phase (Pnma), where the octahedra tilt and deform slightly.