Transport and magnetic properties of La2NiO4+delta (0<=delta<=0.25)

Materials with La2NiO4+delta composition, delta ranging between 0 and 0.25, have been prepared either by solid state reaction or electrochemical oxidation; their electrical conductivity, thermoelectric power, and magnetic susceptibility behaviors are reported. The compounds remain semiconducting in the whole range of composition and, at low temperature, the resistivity increases with delta. The sign of the Seebeck coefficient changes for delta approximate to 0.2 and the thermal variation shows complex behavior. La2NiO4.03 exhibits a thermally activated hopping and an antiferromagnetic ordering, When delta increases, variable range hopping or nearest neighbor hopping, involving at least two types of carriers, can account for the transport properties. The magnetic behavior of materials with delta less than or equal to 0.18 reveals either 3D or 2D magnetic correlations whereas the susceptibility of La2NiO4.25 (La8Ni4O17) follows a Curie-Weiss law below 170 K; a change in the electronic configuration of the nickel ions arises beyond this temperature. (C) 1996 Academic Press, Inc.