SEARCH FOR NEW HIGH-TC OXIDE STRUCTURES

The structures of superconducting La2CaCu2O6, Ba2YCu3O7, TlBa2CaCu2O7, Bi2Sr2CaCu2O8, Pb2YCu3O(x), TlBa2Ca2Cu3O9 with T(c) greater-than-or-similar-to 60 K and semiconducting (Ho, Ce)3Cu2Sr2PbO11 are combinations of u or u' (Ca, Sr)CuO2, v CaTiO3, w' VH or NaCl and x' TiH2 or CaF2 subunits. 122 structures were obtained by combination of up to 8 subunits. 16 of these structures contain the three elements, important for high-T(c) superconductivity: a u' or w' hole donating layer, the v or x' superconducting CuO2 plane and the insulating element u between the CuO2 layers. The unit cell constants and the size of metal atoms of theoretical structures can be estimated from a = 385 pm, c = 160 u + 200 v + 265 (w + x') pm. The coordination numbers CN of metal atoms can be derived from the combining subunits. The oxygen content, formal valence of metal atoms and sum of CN values are related to the number of v and x' units. The metal atoms Cu and Ni or Ti, Tl, Ag, Pb, etc. with 20-30% reduced radii at increased valence are favourable for hole donation in u' or w' units with CN = 4 or 6'.