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Within electron plasma model, a complex crystal of ABСD as a result of phase separation into four subsystems is considered. During the phase transition in the ABCD crystal, the valence bond breaking associated with the crystal lattice destruction. It is caused by the balance energies of the A-B-C-D and A-A, B-B, C-C, D-D 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, B-B, C-C, D-D, with decreasing temperature. It is necessary, that square electron dense plasma energy in the initial phase was essentially much less, than the one in the local phase. This is the condition for the superconducting phase transition in the crystal ABCD. The electron dense plasma parameters in crystals Pd7Se2, Cu3Au, GeNb3, FeSe, MgB2, YBa2Cu3O7, Bi2Sr2Ca2Cu3O10+x, Tl2Ba2Ca2Cu3O10, HgBa2Ca2Cu3O8+x were calculated. q (abcd) = 2β Φ2 (abcd) / (Φ2(a)+ Φ2(b)+ Φ2(c)+ Φ2(d)), where parameters are square Φ2 (M, ρ, s, q, β), square Φ2 (аbcd), square Φ2 (а), square Φ2 (b), square Φ2 (c), square Φ2 (d) are square electron energy in square eV2 crystal abcd, a, b, c, d respectively, Tc is the phase transition temperature, ρ is density, s is valence electron number, M is molecular (atomic) mass, q and β are interaction constants. The equations of the superconducting phase transition curve Tc (q) are derived within the known experimental data and our theoretical parameters. A method for finding the phase transition temperature of a crystal was proposed. From the Tc (q) equation, the parameters of superconductors CuS, LiFeAs, complex oxides of titanium and bismuth, taking into account doping with SrTiO3, BaTiO3, Li2TiO3, BaBiO3, BaKBiO3, were determined.
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