The pressure dependence of visible and near-infrared reflectivity of the superconducting compound ${\mathrm{Ba}}_{0.6}$${\mathrm{K}}_{0.4}$${\mathrm{BiO}}_3$ has been measured to 40 GPa at room temperature. The reflectivity decreases dramatically up to the maximum applied pressure, in marked contrast to copper oxide–based high-${\mathit{T}}_{\mathit{c}}$ superconducting materials.

• Received 22 November 1989

DOI:https://doi.org/10.1103/PhysRevB.41.11576