The superconducting bismuth-based mixed oxides

The present paper describes the synthesis, characterization of mixed-valence bismuthates with three- or two-dimensional perovskite-like structures and structural criteria that influence superconductivity in these compounds. -phase samples of Sr1−xKxBiO3 were prepared for the broad range of K-content: 0.25⩽x⩽0.65. For these bismuthates the symmetry of the structure changes from monoclinic to orthorhombic and finally to tetragonal upon increasing the K-content thus resulting in the decrease of the Bi–O distances and reduction of the network distortions. Superconductivity with maximum Tc=12 K exists in the narrow range (x≈0.5–0.6) within the stability field of the tetragonal phase (0.33⩽x⩽0.65), when the three-dimensional octahedral framework has close to the ideal perovskite structure arrangement. yered type (Ba,K)3Bi2O7 and (Ba,K)2BiO4 bismuthates belonging to the An+1BnO3n+1 homologous series were investigated. Buckling of the (BiO2) layers in the structure of the n=2 member occurs due to the ordering of alkaline- and alkaline-earth cations between two independent positions. The formation of the one-layer bismuthate was revealed by Electron Microscopy and XRPD studies. Both types of compounds are considered to be possible candidates for new superconducting materials among bismuthates.