Phase segregation in the Gd1-xSrxFeO3-δ series

Gd1-xSrxFeO3-delta ferrites have been studied by means of X-ray powder diffraction in the whole composition range. Single-phase solid solution is found for x < 0.09 and for x > 0.63. At intermediate Sr content, phase segregation takes place. Compounds with x <= 0.05 crystallize in the orthorhombic structure, space group Pbnm. Oxygen-deficient Gd1-xSrxFeO3-delta with x >= 2/3 are cubic or nearly cubic. The oxygen vacancies stabilize the cubic phase for x = 2/3 whereas highly oxidized samples show an orthorhombic distortion, which has not been observed earlier. Magnetic and electrical properties have been measured for the single-phase solid solutions. Gd1-xSrxFeO3-delta compounds with x >= 2/3 order antiferromagnetically below similar to 100 K. In the paramagnetic region, their susceptibility follows the Curie-Weiss law in all but SrFeO2.96 compound. These ferrites show semiconducting behavior in the electrical transport likely related to atomic disorder. We find that the conductivity activation energy becomes larger by increasing either the Gd content or the oxygen vacancies. (C) 2005 Elsevier Inc. All rights reserved.