Synthesis and physical properties of new superconducting bismuthates, K1-xAxBiO3 (A=Bi, La, and Ca), are reported. New compounds could only be prepared in a narrow range of composition, restricted by the A-site cation size, with cubic perovskite structure. For the first two systems (A = Bi, La), Tc was found to depend strongly on composition and was enhanced upon heterovalent substitution. The data obtained and comparison with known bismuthates show undoubtedly that band filling controlled by dopant concentration is a crucial parameter for variation of Tc in this class of materials.
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