Superconductivity near 30 K without copper: the Ba_0.6K_0.4BiO₃ perovskite

Abstract

It is well known that the breakthrough of Bednorz and Müller¹ in discovering superconductivity in (La, Ba)₂CuO₄ was inspired in part by their knowledge of the superconducting properties of Ba(Pb, Bi)O₃ (ref. 2). With a transition temperature, T_c, of ∼12 K, that compound was not generally considered anomalous despite the fact that its T_cis 3–5 times higher than that of traditional superconductors with comparable density of states^3–5. The increases in T_c for copper-oxide-based materials continue to generate worldwide excitement, but from both a chemical and theoretical point of view it would also be exciting if high-T_csuperconductivity were observed in another class of materials. Here we report the results of experiments leading us to the single-phase perovskite Ba_0.6K_0.4BiO₃, which has a magnetically determined onset temperature of 29.8 K—a T_c considerably higher than that of conventional superconductors and surpassed only by copper-containing compounds. Superconductivity in this compound occurs within the framework of a three dimensionally connected bismuth-oxygen array. These results suggest that further research toward exploring the limiting T_cs for bismuth-oxide-based, high-temperature superconductors might be fruitful.