Within oscillation electron model the superconducting crystal AB is considered consisting of two subsystems for phase separation. During the phase transition in the AB crystal, the valence bond breaking associated with the crystal lattice destruction. It is caused by the balance energies of the AB and A-A, B-B bonds. The basic principle of the phase transition is caused by bonds being broken and dumbbell configurations of atoms are formed.

The pairing of electrons is guided by a plasma mechanism. Free electrons couple to lower system energy. When molecules are formed from individual atoms by dumbbell configuration, energy is released. The energy balance is caused by a change in the distances between atoms A-A and B-B with decreasing temperature. It is necessary, that square electron plasma energy in a local phase was essentially much less, than the one in an initial phase. This is the condition for the superconducting phase transition in the crystal AB.

The equations of the superconducting phase transition curve Tc(q) are derived within the known experimental data and our theoretical parameters Φ (M, ρ, s, q, β), where square Φ (аb), square Φ (а), square Φ (b) is square electron energy in square eV crystal AB, A, B, respectively, Tc is the phase transition temperature, ρ is density, s is valence electron number, M is molecular (atomic) mass, q and β are parameters. The electron plasma parameters of iron selenide FeSe, magnesium diboride MgB2, complex cuprates YBaCuO, mixed compounds of silver Ag2O and gold oxide Ag3AuS2 were calculated.