The investigation of mechanical characteristics was based on the calculations of the elastic properties determined by performing finite distortions of the lattice and deriving the elastic constants from the relationship strain-stress. The mechanical properties as derived from the elastic constants C ij are described by bulk (B) and shear (G) moduli. The method used for obtaining the two moduli is that derived by Voigt , based on a uniform strain. The calculated sets of elastic constants are given in Table . All values are positive. Their combinations obeying the rules pertaining to the mechanical stability of the phase, and the equations providing the bulk B V and shear G V moduli for the tetragonal system are as follows : The calculated values for all three novel phases in Table exhibit large B V of the order of 400 GPa.