All C ij values are positive, suggesting mechanically stable phases. qtz C 6 has the largest C ij values, while qtz BP and qtz AlP have significantly smaller elastic constants. The new phases are fully described by the bulk (B), shear (G) and Young's (E) moduli obtained by Voight's averaging of the elastic constants using ELATE software . The last three columns of Table show the elastic moduli, with values that follow the trends observed for C ij . It is evident that AlP is significantly more compressible than BP, both in the case of the cubic (zb) and the hexagonal (qtz and NiAstype) phases.