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.
Single-phase samples of Sr 1Γx K x BiO 3 were prepared for the broad range of K-content: 0:25 6 x 6 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 T c ΒΌ 12 K exists in the narrow range (x % 0:5-0.6) within the stability field of the tetragonal phase (0:33 6 x 6 0:65), when the threedimensional octahedral framework has close to the ideal perovskite structure arrangement.
The layered type (Ba,K) 3 Bi 2 O 7 and (Ba,K) 2 BiO 4 bismuthates belonging to the A nΓΎ1 B n O 3nΓΎ1 homologous series were investigated. Buckling of the (BiO 2 ) layers in the structure of the n ΒΌ 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.