STRUCTURE, MICROSTRUCTURE AND MAGNETO-TRANSPORT PROPERTIES OF Pr_(1-x)B_xCoO_(3-δ) (B~(2+)= Ba~(2+), Ca~(2+)) PEROVSKITE MATERIALS

摘要

We have used the "Pechini" method for the efficient preparation of Pr_(1-x)B_xCoO_3 (B~(2+) = Ba~(2+), Ca~(2+)) samples. According to the XRD data, the so-obtained samples present an orthorhombic symmetry (≈2~(1/2) a_c x ≈ 2a_c x ≈2~(1/2) a_c) for x≤0.30 (B~(2+) = Ba~(2+), Ca~(2+)), while the Pr_(0.5)Ba_(0.5)CoO_3 compound has a tetragonal symmetry (a = b ≈ a_c and c ≈ 2a_c) and Pr_(0.6)Ba_(0.4)CoO_3 is a mixture of an orthorhombic and a tetragonal phase. Nevertheless, in the case of the Pr_(0.5)Ba_(0.5)CoO_3 ED reveals the presence of extra order, probably related to the ordering of oxygen vacancies whose number increases with x and is highest for x = 0.50. The magnetic and transport properties of these materials change upon doping: as x increases the samples tend to a ferromagnetic behavior and their resistivity tends to diminish. A peculiar magnetotransport behavior is found in the compounds.