Dilute Metals: Superconductivity, Critical Currents, Magnetic Properties
  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. 
V.N.Bogomolov