Metal-insulator transition in double perovskite Sr2Fe(Re,W)O6 compound

In this report, we present results of systematic studies of X-ray, electrical resistivity (p) and thermoelectric power (TEP, S) on polycrystalline Sr2FeRe1-xWxO6 (x = 0-1.0) samples. For the undoped Sr2FeReO6 (x = 0) sample, analysis of the p(T) data suggests that the electron-electron scattering plays a major role in governing the conduction mechanism. The resistivity data of the low doped samples (x = 0.1-0.2) exhibits metal-insulator transition. For samples with x = 0.3-1.0, the electrical transport at low temperatures behaves like that of a semiconductor/insulator, where p(T) data show close agreement with Mott's variable range hopping theory implying weak localization of the charge carriers. On the other hand, at high temperatures the charge conduction follows thermally activated semiconductor type character. For all the samples, S is found to be positive indicating hole conduction. The samples with x = 0-0.2 show almost linear dependence of S on T. The Fermi energy estimated from the slope of the S(T) curves ties in the range 0.5-0.3 eV for samples with x = 0-0.2. For samples with x = 0.3-0.6, S(T) data show a broad peak which shifts to a low-temperature side as x increases. This feature has been qualitatively discussed in the light of percolation model. (C) 2003 Elsevier B.V. All rights reserved.