A series of compounds with composition BaxLa1–xCoO3 (0 ≦ x ≦ 0.5) is synthesized. The rhombohedrally distorted perovskite LaCoO3 becomes cubic at x = 0.4. The electrical resistivity of the samples decreases with increasing x and the minimum lies between x = 0.2 and 0.3. The compounds with x ≧ 0.2 are ferromagnetic, but also possess a paramagnetic moment. At x = 0.5 the compound is metallic. The results can be explained by Zener double exchange as well as by Goodenough's itinerant electron ferromagnetism.

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Structure and electrical properties of two perovskite systems LaCo1−xMnxO3 and LaCo1−xFexO3 (0 ≦ x ≦ 1) are described. A phenomenological phase diagram based on the relation between cation radii rA, rB and the void radius at the A‐site is proposed that rationalises most of the existing structural data. Results on measurements of electrical resistivity and Seebeck coefficient are discussed.