TRANSPORT AND MAGNETIC-PROPERTIES OF R-EQUAL-TO-DELTA-LESS-THAN-OR-EQUAL-TO-0.25)(DELTA (0)

Materials with La2NiO4+delta composition, delta ranging between 0 and 0.25, have been prepared either by solid state reaction or electrochem ical oxidation; their electrical conductivity, thermoelectric power, a nd magnetic susceptibility behaviors are reported. The compounds remai n semiconducting in the whole range of composition and, at low tempera ture, the resistivity increases with delta. The sign of the Seebeck co efficient changes for delta approximate to 0.2 and the thermal variati on shows complex behavior. La2NiO4.03 exhibits a thermally activated h opping and an antiferromagnetic ordering, When delta increases, variab le range hopping or nearest neighbor hopping, involving at least two t ypes of carriers, can account for the transport properties. The magnet ic behavior of materials with delta less than or equal to 0.18 reveals either 3D or 2D magnetic correlations whereas the susceptibility of L a2NiO4.25 (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.