  Traditionally, when one describes the crystallographic structure of oxides,
the oxygen ion radius r02 is assumed to be approximately equal to 1.4A. The
oxygen ions occupy in this case 80-90% of the crystal volume. Metal atoms are
considered then as ions playing a role of donors with rather small radius of
(0.5 - 0.8) A. However, the atomic packing picture and, therefore, physical
properties such as electric conductivity and superconductivity of oxides will
be essentially different, if we assume r02- ~ 0.56 A. Such magnitude of the
radius is known from the quantum mechanics calculations [2]. According to this
picture, 80-90 % of the crystal volume is occupied by the metal atom orbitals
with radius (1.3-1.9) A, while the oxygen ions play a role of acceptors, which
reduce occupancy of these orbitals ("indirect" dilution of the metal). A
"direct" dilution of metals takes place in stoichiometric matrices. When
r02-~0.56 A, channels with diameter 3.6 A present in the hexagonal matrix
Ag3Pb2H2O6 directed along the "c" axis.
  The channels are filled by chains of the Ag2 molecules with atomic diameter
of 2.6 A and the molecule concentration n_B = 25.6 10^20 cm^-3.
  The Bose-Einstein condensation (BEC) temperature T_cB ~ 400K is calculated
for the electron effective mass value m*=7.5m_e, where m_e is the isolated
electron mass. Three-dimensional networks of Na2 chains form in Na solutions in
NH3 and WO3 as well (respectively, with n_B=4.71 10^20 cm^-3;
  T_c sim 180K; m*=5.0m_e and n_B=4.74 10^20 cm^-3; T_c sim 91K; m*=10m_e).
Close magnitudes of the Ag2 and Na2 chains parameters respectively in NH3 and
WO3 favors the opinion that all these structures have a composite structure and
similar mechanisms of the high temperature superconductivity.
