Two-component structure of metal-oxide superconductors

Abstract

Similar essential properties of Ba-K-Bi-0 (BKBO) bismuthate and cuprate superconductors imply a common pairing mechanism in spite of the apparent isotropic structure of bismuthates being contradictory to the two-dimensional structures of cuprates. However, this distinction is likely not to be the case as structural studies of BKBO materials composed of nm-sized domains of two phases, superconducting and semiconducting, have not revealed true structures of BKBO superconducting phases. The thorough studies of phase relations in the Ba-Bi-O (BBO) parent system have resulted in the discovery of a large number of discrete barium-bismuth oxides. Bi-rich layered oxides are assumed to be matrices intercalated with potassium and transformed into layered superconductors with ordered ion arrangements. The structures of samples corresponding to two-phase regions formed of Ba-rich oxides and the prime perovskite BaBiO3 have been found to be disordered. We believe that phase relations in the form of discrete compounds and disordered materials are inherent in any metal-oxide systems including superconducting ones. The two-component structure of oxide superconductors is due to the synthesis of superconducting materials run under conditions of simultaneous formation of two phases.