Effect of increasing Sr content on structural and physical properties of K2NiF4-type phase GdSrFeO4

The structural, magnetic and electrical properties of Gd1-xSr1+xFeO4 (0 <= x <= 0.4) have been discussed in terms of the mixed valence state of Fe (Fe3+/Fe4+). The Rietveld refinements of powder X-ray diffraction data reveal that all the phases crystallizes with tetragonal unit cell in the space group I4/mmm. The lattice constant a decreases while there is increase in c parameter with increase in x. All the phases are antiferromagnetic and the increase in Weiss constant (theta(P)) with Sr2+ content could be attributed to the generation of the Fe4+ ions which introduces the ferromagnetic double-exchange Fe3+-O2--Fe4+ interactions. The materials show semiconducting behavior and the electronic conduction in these materials is obtained via hopping of electrons from the occupied sites, Fe3+ ions, to the unoccupied sites, Fe4+ ions.