Systematics in the electron transport and magnetic properties of LnBO₃ perovskites

Abstract

Systematics in the electrical and magnetic properties of transition metal perovskites LnBO₃ (Ln=rare-earth ion, B=3d transition metal) with the variation of Ln and B ions are reviewed. The electrical resistivity and activation energy of LnBO₃ compounds increase with the decreasing size of the Ln³⁺ ion for a given B ion. The low-spin to high-spin transition temperature of Co³⁺ ion in LnCoO₃ similarly increases with the decrease in size of Ln³⁺ while the magnetic ordering temperatures in LnVO₃, LnFeO₃, LnCrO₃ and LnSrCo₂O₆ decreases with decreasing size of the rare-earth ion. These results may be understood in terms of the increasing acidity of the rare earth ion with decreasing size and the competition between the Ln³⁺ and the B³⁺ ions for covalency with the oxygen ions. The effect of this competition on the metal oxygen covalency and crystal field parameter is discussed in relation to the results obtained and Goodenough's phase diagram. The possibility of d-f exchange interaction in La_1-xLn_x NiO₃ is also discussed in the light of ESR results.