Thermoelectric power of Ba_1-xK_xBiO₃

We report measurements of thermoelectric power of two superconducting samples of Ba_1-xK_xBiO₃ 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 Ba_1-xK_xBiO₃ 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.