Predicted crystal structures of SiCN compounds. The calculation of total enthalpy with pressure indicates that (a) t-SiCN may change into (b) h-SiCN and (c) o-SiCN under high pressures of 21.9 and 21.6 GPa, respectively.^[116] (a) t-SiCN was a narrow gap semiconductor with a band gap of 0.89 eV, and (b) h-SiCN and (c) o-SiCN are metallic. The calculated hardness of (a) t-SiCN is 41.5 GPa. The Si, C, and N atoms are painted in blue, brown and white colors, respectively.