The study of the $BiO_{6}$ octahedra structure in superconducting $Ba_{0.6}K_{0.4}BiO_3$ single crystal by extended x-ray absorption spectroscopy

EXAFS에 의한 $Ba_{0.6}K_{0.4}BiO_3$ 단결정의 초전도 상태에서 $BiO_{6}$ octahedra 구조의 연구

We have observed the temperature dependences of Bi $L_{III}$ edge spectra by extended X-ray absorption spectroscopy for a high quality single crystal and a powder of the $Ba_{0.6}K_{0.4}BiO_3$ superconductor. $Ba_{0.6}K_{0.4}BiO_3$ has the cubic structure and metallic states. The deformation of the $BiO_{6}$ octahedra, which is due to the anomalies of the Bi-O and Bi-Ba bond length, was showed by the double-shell fit. It was clearly found that these anomalies are owing to the difference in the strength of Bi-O bonds. The temperature dependences of both bond lengths and the Debye-Walter factor ${\sigma}^2$ of the Bi-O and Bi-(Ba,K) bond are discussed to illustrate local structural features of the $Ba_{0.6}K_{0.4}BiO_3$