The superconducting bismuth-based mixed oxides

摘要: The present paper describes the synthesis, characterization of mixedvalence bismuthates with 3- or 2-dimensional perovskite-like structures and structural criteria that influence superconductivity in these compounds. Single phase samples Sr1−x K x BiO3 were prepared for broad range K-content: 0.25≤x≤0.65. For symmetry structure changes from monoclinic to orthorhombic finally tetragonal upon increasing K-content thus resulting decrease Bi-O distances reduction network distortions. Superconductivity maximum T c=12K exists narrow (x≈0.5–0.6) within stability field (0.33≤x≤0.65), when 3-dimensional octahedral framework has close ideal perovskite arrangement. At same time compositions optimal Bi-valence (x=0.33 0.43) do not show any sign superconductivity, probably, due layered type (Ba, K)3Bi2O7 K)2BiO4 belonging A n+1B n O3n+1 homologous series investigated. Buckling (BiO2) layers n=2 member was revealed. formation n=1 bismuthate found by Electron Microscopy X-ray powder diffraction studies. Both types compounds are considered be possible candidates new superconducting materials among bismuthates.