Structural and superconducting properties of isoelectronic Sb-substituted Ba1−xKxBiO3

Abstract Single phase samples of (Ba 1− x K x )(Bi 1− y Sb y )O 3 have been synthesized over a limited compositional range using a two-step procedure: high-temperature firing in a low oxygen partial pressure followed by low-temperature oxygen annealing. For y > 0 samples are superconducting only in a simple cubic structure with T c gradually decreasing as y increases for fixed x . As in the case of potassium only ( y =0) substituted material, the highest T c is found in the compositional range adjacent to the structural phase transition into the lower symmetry nonsuperconducting phase. Mossbauer effect measurements indicate that Sb is close to +5 valent state with small mixed valent behavior which increases with Sb content.