Within inharmonious plasma oscillation model the superconducting crystal AB is considered consisting of two
subsystems 2AB=A2+B2. In high-temperature superconductors spontaneous division into two phases: superconducting
and isolating was revealed. Phase separation was caused by plasma instability. It is obtained the transition
superconducting phase temperature dependence Tc = F (q12, q1, q2, V12, V1, V2) on the isotopic substitution physical
parameters: q – initial and component interaction parameters, V - volume in initial and component crystal lattices. The
isotopic transition superconducting phase temperature displacement ΔTc is associated with the change of the initial and
component interaction and crystal lattice parameters. From the plasma mechanism of superconductivity follows
superconducting crystals exist at room temperature.