Spin-state transition, magnetic, electrical and thermal transport properties of the perovskite cobalt oxide Gd0.7Sr0.3CoO3

摘要

The magnetization, resistivity p, thermoelectric power (TEP) S, and thermal conductivity (K) in perovskite cobalt oxide Gd0.7Sr0.3CoO3 have been investigated systematically. Based on the temperature dependence of susceptibility chi(g)(T) and Seebeck coefficient S(T), a combination of the intermediate-spin (IS) state for Co3+ and the low-spin (LS) state for Co4+ can be suggested. A metal-insulator transition (MIT) caused by the hopping of sigma* electrons (localized or delocalized e(g) electrons) from the IS Co3+ to the LS Co4+ is observed. Meanwhile, S(T) curve also displays an obvious phonon drag effect. In addition, based on the analysis of the temperature dependence of S(77) and p(T), the high-temperature small polaron conduction and the low-temperature variable-range-hopping conduction are suggested, respectively. As to thermal conduction (K)(T), rather low (K) values in the whole measured temperature range is attributed to unusually large local Jahn-Teller (JT) distortion of Co3+ O-6 octahedra with IS state. (c) 2006 Elsevier Ltd. All rights reserved.