Mat. Res. Bull. Vol. 8, pp, 423-432, 1973. Pergamon Press, Inc. Printed in the United States. INTERPRETATION OF THE TRANSPORT PROPERTIES OF La2NiO 4 AND La2CuO 4 COMPOUNDS* J. B. Goodenough Lincoln Laboratory, Massachusetts Institute of Technology Lexington, Massachusetts 02173 (Received February 5, 1973; Communicated by J. B. Goodenough) ABSTRACT Resistivity and thermoelectric-power data for the tetragonal compounds . "En2NiO 4 and La2CuO 4 are interpreted qualitatively in terms of narrow energy bands of strongly correlated d-like electrons. Experimental Situation The compounds Ln2NiO 4 and Ln2CuO 4, where Ln is a rare-earth ion, crystal- lize in the tetragonal K2NiF 4 structure (1, 2), which consists of alternate KF rocksalt and KNiF 3 perovskite layers along the c-axis. A small distortion to orthorhombic symmetry below 533K in La2CuO 4 (1) has little apparent influence on the transport properties (2) and is therefore ignored in the present discussion. The magnetic susceptibility of La2CuO 4 is less than 10 -6 emu/g from room temperature to 4.2K in fields to 17 kOe (1). The susceptibility of La2NiO 4, on the other hand, exhibits a Curie-Weiss law with ~ P= -500K and Ueff = 3.7u B per Ni 2+ ion (3), which is significantly larger than the localized, spin-only value of 2.82U B. The temperature coefficients of the resistivities of sintered bars of La2NiO 4 and Nd2NiO 4 are negative (semiconducting) for T < 500K and positive (metallic) for T > 600K. Furthermore, the temperature coefficient of the thermoelectric power also changes sign, from negative to positive, in the interval 500 < T < 600K (2). *This work was sponsored by the Department of the Air Force. 423