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) Å, b = 7.5854(3) Å, c = 11.6425(4) Å and β = 100.971(2)°. The monoclinic structure of Sm2FeTaO7 showed an arrangement of alternating Smsingle bondO and Fe/Tasingle bondO layers and two types of irregular octahedra of Fe/Tasingle bondO, 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 (Eg) of Sm2FeTaO7 has a low value of around 2.0 eV.