2-COMPONENT STRUCTURE OF METAL-OXIDE SUPERCONDUCTORS

Similar essential properties of Ba-K-Bi-0 (BKBO) bismuthate and cuprat e superconductors imply a common pairing mechanism in spite of the app arent isotropic structure of bismuthates being contradictory to the tw o-dimensional structures of cuprates. However, this distinction is lik ely not to be the case as structural studies of BKBO materials compose d of nm-sized domains of two phases, superconducting and semiconductin g, have not revealed true structures of BKBO superconducting phases. T he thorough studies of phase relations in the Ba-Bi-O (BBO) parent sys tem have resulted in the discovery of a large number of discrete bariu m-bismuth oxides. Bi-rich layered oxides are assumed to be matrices in tercalated with potassium and transformed into layered superconductors with ordered ion arrangements. The structures of samples correspondin g to two-phase regions formed of Ba-rich oxides and the prime perovski te BaBiO3 have been found to be disordered. We believe that phase rela tions in the form of discrete compounds and disordered materials are i nherent in any metal-oxide systems including superconducting ones. The two-component structure of oxide superconductors is due to the synthe sis cf superconducting materials run under conditions of simultaneous formation of two phases.