Relationship between crystal structure and electrical property of K2NiF4-type (Ca1-xNd1-x) CoO4-δ

K2NiF4-type (Ca1-xNd1+x)CoO4-delta (0.0 less than or equal to x less than or equal to 0.2) was synthesized and found to have a tetragonal structure with a space group I4/mmm. The Rietveld method indicates that distortion in the CoO6 octahedron decreases gradually with increasing x. Although (Ca1-xNd1+x)CoO4-delta is paramagnetic above 80 K, the (1/chi)-T curve does not follow the Curie-Weiss law. (Ca1-xNd1+x)CoO4-delta is an n-type semiconductor, and its thermopower varies linearly with temperature. The X-ray photoelectron spectroscopy measurement indicates that the binding energy of the Co (2)p(3/2) level shifts toward the high binding energy site with increasing Co2+ ion content. The electrical property of (Ca1-xNd1+X)CoO4-delta is explained using the model of transport by activated hopping of carriers. Since the gradual increase in the Co-O(l) distance prevents electron transfer in the Co2+-O(1)-Co3+ path, both the electrical resistivity and the activation energy increase with increasing x. (C) 2003 Elsevier B.V. All rights reserved.