Superconductivity above 20 K in the Ba-K-Bi-O system

Abstract

The results of magnetic susceptibility measurements on multiphase Ba-K-Bi-O samples with overall composition ${\mathrm{Ba}}_{0.9}$${\mathrm{K}}_{\mathrm{x}}$${\mathrm{BiO}}_{3}$ (x\ensuremath{\approxeq}0.2) provide evidence for superconductivity above 20 K in a minority fraction (\ensuremath{\sim}5%) of the sample volume. These results support the expectation that K doping at the inactive Ba donor sites can extend the metallic range of the previously studied ${\mathrm{BaPb}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Bi}}_{\mathrm{x}}$${\mathrm{O}}_{3}$ alloys closer to the ${\mathrm{BaBiO}}_{3}$ Peierls instability where the strong coupling of the conduction electrons to the O phonons could explain the enhanced (${T}_{c}$\ensuremath{\sim}22 vs 13 K) superconducting transition temperatures.