  Properties of oxides are interpreted as a result of existence of the virtual
sublattices formed by the atomic quantum states. An infinite cluster with the
superconductivity of the Bose-Einstein condensate kind can be formed in the
ground state sublattice at certain oxigen atoms concentration in the
effectively diluted system of metal atoms (above the percolation threshold).
Then the electron pairs concentration n/2 can be much less than the metal atoms
concentration N in the oxide. The similar situation takes place in metals with
superconductivity of the BCS type. Above the percolation threshold the
superconductivity Tc may be limited by the magnetic properties of the oxigen
2p4quantum state sublattice. Data on the critical current density allow us to
estimate the electronic pair density n/2 and to obtain an information
concerning the superconductivity nature.
