Stability of carbon nitride solids

Abstract

An ab initio variable-cell-shape molecular-dynamics algorithm is used to investigate the stability of three carbon nitrides with composition ${\mathrm{C}}_{3}$${\mathrm{N}}_{4}$. The hexagonal \ensuremath{\beta}-${\mathrm{C}}_{3}$${\mathrm{N}}_{4}$ structure, which has been the subject of earlier investigations, is refined and its metastability is verified. Two other metastable structures are identified: a structure resembling zinc-blende CN with one C vacancy per cubic cell and a structure resembling graphitic CN with one C vacancy per four N sites. Both the refined \ensuremath{\beta} phase and the cubic phase have compressibilities comparable to that of diamond. The graphitic and the \ensuremath{\beta} phases lie very close in energy and are slightly favored over the cubic phase.