  Structures and parameters of some high and low temperature superconductors
(HTSC, LTSC) are considered basing on the alternative estimate of the O2- ion
radius magnitude (0.5-0.6) A. Phase transitions into the superconducting state
are considered as the Bose-Einstein condensation (BEC). The super HTSC with Tc
= 371 K (YBa2Cu3Se7) and TC ~ 400K (Ag2(Ag3Pb2H2O6)) and LTSC with Tc~0.3K
(SrNbxTi(1-x)O3) are shown to be of the BEC type. Instability of the structure
of the first one results from higher magnitude of the Se2- ion radius in
comparison with the O2- radius. The second one forms quasi one-dimensional
structures and is rather inpractical. The electron density and the effective
mass are estimated for some stoichiometric and non-stoichiometric
(nano-composite) high temperature superconductors, which have some peculiar
features. Large effective masses can indicate existance of polarons
(bipolarons) in such systems. Some new superconductors MgxWO3.
