Superconductivity in (Ba,K)SbO 3 .

(Ba,K)BiO 3 constitute an interesting class of superconductors, where the remarkably high superconducting transition temperature T c of 30 K arises in proximity to charge density wave order. However, the precise mechanism behind these phases remains unclear. Here, enabled by high-pressure synthesis, we report superconductivity in (Ba,K)SbO 3 with a positive oxygen-metal charge transfer energy in contrast to (Ba,K)BiO 3 . The parent compound BaSbO 3-δ shows a larger charge density wave gap compared to BaBiO 3 . As the charge density wave order is suppressed via potassium substitution up to 65%, superconductivity emerges, rising up to T c  = 15 K. This value is lower than the maximum T c of (Ba,K)BiO 3 , but higher by more than a factor of two at comparable potassium concentrations. The discovery of an enhanced charge density wave gap and superconductivity in (Ba,K)SbO 3 indicates that strong oxygen-metal covalency may be more essential than the sign of the charge transfer energy in the main-group perovskite superconductors.