Monolithic ceramic bodies that have a mixed-oxide marginal region and a metallic surface, where the ceramic body includes an oxide of a first metal (I), while the mixed-oxide marginal region includes the oxide of the first metal (I) and the oxide of a further metal (II) having a high affinity for oxygen, and the metallic surface includes the further metal (II). The mixed oxide marginal region includes a continuous concentration gradient of the first metal (I), from 100% in the core to 0% in the transitional region to the metallic surface of the ceramic body, and a continuous concentration gradient of the further metal (II), starting from 0% in the core to 100% in the transitional region to the metallic surface of the ceramic body, where the oxygen concentration in the mixed-oxide marginal region remains constant, and the monolithic structure of the ceramic body has no phase boundaries.