Synthesis by two methods and crystal structure determination of a new pyrochlore-related compound Sm2FeTaO7

This paper reports on the synthesis of a new pyrochlore-related compound Sm2FeTaO7 by both solid state reaction and sol-gel synthesis routes. Structural features were determined by X-ray powder diffraction and Rietveld refinement and were corroborated using Transmission Electron Microscopy (TEM). The results revealed that Sm2FeTaO7 crystallized in the monoclinic system with space group C2/c and the following cell parameters: a = 13.1307(5)angstrom, b = 7.5854(3)angstrom, c = 11.6425(4)angstrom and beta = 100.971(2)degrees. The monoclinic structure of Sm2FeTaO7 showed an arrangement of alternating Sm-O and Fe/Ta-O layers and two types of irregular octahedra of Fe/Ta-O, which are interconnected into a hexagonal tungsten bronze (HTB)-type network. On the other hand. Sm2FeTaO7 prepared by sol-gel was obtained with lower particle sizes than the solid state produced compound. The difference in particle size causes a difference of one order of magnitude in the specific surface area. In addition, energy band gap (E-g) of Sm2FeTaO7 has a low value of around 2.0 eV. (C) 2012 Elsevier B.V. All rights reserved.