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

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≊0.2) provide evidence for superconductivity above 20 K in a minority fraction (∼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{-}\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 ($T_c$∼22 vs 13 K) superconducting transition temperatures.