Electrical properties and spin state of the Co3+ ion in (Nd1-xGdx)CoO3

Orthorhombic perovskite-type (Nd1-xGdx)CoO3 was synthesized in the range 0.0less than or equal toxless than or equal to1.0. Rietveld analysis indicates that an average Co - O distance is independent of x. The Co - O(1) - Co angle has a maximum value at x - 0.2 - 0.4, while the Co - 0(2) - Co angle decreases with increasing x. From measurements of the electrical resistivity (rho) and the Seebeck coefficient (alpha). (Nd1-xGdx)CoO3 exhibits hopping conductivity at high temperature. Deflection points (T-L and T-H) are observed in the log rho-1000/T curve. and these points correspond to a change in the spin state of the CO3+ ion. (C) 2002 Elsevier Science B.V. Ail rights reserved.