Superconductivity near 30 K was discovered recently in a copper-free phase, Ba1-xKxBiO3 (refs 1, 2). This material has structural and electronic properties in common with both the cuprate high-transition-temperature (high-Tc) superconductors and with BaPb1-xBixO3, which has a Tc of ∼12 K (ref. 4). Here we report the growth and structural characterization of single crystals of Ba1-xKxBiO3. A maximum Tc of 30.5 K is found from d.c. susceptibility measurements for crystals of approximate composition Ba0.6K0.4BiO3. The structure for a crystal with x = 0.37 is determined by X-ray diffraction and is found to be a simple cubic perovskite with a = 4.2869 (6) Å. A commensurate lattice distortion occurs for x = 0.04, which is identified as a distortion of the BiO6 octahedra. Effects of structural distortions and concomitant changes in electronic properties in this non-magnetic system may contain clues to the role of phonons and electronic interactions in the microscopic pairing mechanism of high-Tc superconductors.
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