Thermoelectric power of ${\mathrm{Ba}}_{1\mathrm{-}\mathit{x}}$${\mathrm{K}}_{\mathit{x}}$${\mathrm{BiO}}_3$

We report measurements of thermoelectric power of two superconducting samples of ${\mathrm{Ba}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{K}}_{\mathit{x}}$ ${\mathrm{BiO}}_3$ with differing resistivity behaviors. The thermopower is negative between 50 and 300 K. We find in both samples an unusual temperature dependence similar to that in high-oxygen-content samples of Y-Ba-Cu-O with negative thermopower, suggesting a common mechanism producing this behavior in ${\mathrm{Ba}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{K}}_{\mathit{x}}$ ${\mathrm{BiO}}_3$ and the Cu-O-plane superconductors. Our sample with an activated temperature dependence of resistivity shows a change to positive thermopower before becoming superconducting, possibly due to the effect of nonmetallic grain boundaries.