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In rare earth cobaltites, the cobalt ions are present mainly in the diamagnetic low‐spin CoIII state at low temperatures. The CoIII ions transform to high‐spin Co3+ ions with increase in temperature. At higher temperatures, there is electron‐transfer from Co3+ to CoIII ions producing intermediate states. We see spin‐state transitions in these cobaltites in the range 250–870 K. At very high temperatures, the cobaltites show evidence for localizeditinerant electron transitions. In La1−xSrxCoO3, there is onset of ferromagnetism at x > 0.125, at which point there is a structural discontinuity and electrons become itinerant. The composition with x = 0.5 is metallic and Tc = 230 K. The ferromagnetic component in La1−xSrxCoO3, increases with x in the range 0.125–0.50. In LaCo1−xFexO3, the iron ions are always present in the high‐spin state and the d‐electrons get more localized with increase in x. Effect of substitution by ions like Th4+ and Ni3+ in LaCoO3 have also been examined. Catalytic properties of rare earth cobaltites appear to be related to the spin state equilibria.
The electrical and magnetic properties of NdTiO3+δ have been measured and correlated with unit cell parameters and composition of the samples. NdTiO3+δ exhibited the GdFeO3-type structure across the whole of the composition range, which in our investigations was found to extend approximately from NdTiO3.05 to NdTiO3.15. Over this range, the lattice contracted slightly, consistent with a rotation of the TiO6 octahedra in the a–c plane. At compositions closest to NdTiO3.05, the materials were semiconducting and displayed a ferromagnetic transition at a temperature of about 90K. At compositions above about NdTiO3.11, the materials were metallic and did not show any magnetic transitions. Several samples of composition close to NdTiO3.11 showed a metal–insulator transition at typically ∼105K. Electron microscopy revealed the presence of a microdomain texture in some samples, indicating that the results apply to an average structure rather than a genuine single phase. The results mirror those found for non-stoichiometric LaTiO3+δ and can be explained in a similar fashion.
