Anomalous Electrical Behavior in Ferromagnetic La1-xBaxCoO3-δ Materials (0 < x ≤ 0.50)

We prepared in this work La(1-x)Ba(x)CoO(3-delta) (0 < x <= 0.50) compounds using the nitrate decomposition method, and focus in the study of the transport properties of the ferromagnetic compounds (x > 0.15, T(c) similar to 200 K) in the temperature range 77 K <= T <= 300 K. We find that while for x < 0.20 these materials show semiconducting behavior, their electrical conduction being dominated by small-polaron holes, for x > 0.20 they show metallic behavior for T > 100 K, with a transition to semiconducting behavior being observed for T <= 100 K. For x = 0.20, small changes in the oxygen stoichiometry of the samples - due to slight variations in the thermal treatments - greatly affect the transport properties of the materials that can show either two metal-insulator transitions as the temperature increases or a semiconducting behavior. Very interestingly all these ferromagnetic samples are very sensitive to the polarity of the applied electrical current, and display peculiar "diodic" behaviors. All these observations are explained on the basis of an inhomogeneous electronic structure in the Ba-doped cobalt perovskites.