Phase stability and properties of the hole doped perovskite cobaltites (La1-xRx)0.7Ba0.3CoO3-δ (0.0≤x≤1.0; R = Pr, Nd)

The structural, magnetic and electrical properties of the hole doped cobaltites, with compositions (La1-xRx)(0.7)Ba0.3CoO3 (0.0 less than or equal to x less than or equal to 1.0; R = Pr, Nd), have been studied. Substitutions of Pr and Nd for La destabilize the stoichiometric perovskite structure at the benefit of the ordered oxygen deficient perovskite '112'-type structure, due to decrease in size of the rare earth ion. Our studies show that for our synthesis condition, the samples of nominal compositions, R1-yBayCoO3 (R = Pr, Nd), can form with the perovskite structure only for y < 0.3. In the single-phase regions, the thermo-magnetic irreversibility and coercive field increase with the substitution of Pr and Nd for La. The low temperature resistivity minimum and negative magneto-resistance in the insulating regions of these polycrystalline compounds have been ascribed to grain boundary effects. (C) 2002 Elsevier Science Ltd. All rights reserved.