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 SmO and Fe/TaO layers and two types of irregular octahedra of Fe/TaO, 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.

The monoclinic (space group C2/c) structure of a new compound, Sm2FeTaO7 shows an alternating SmO and Fe/TaO layers. In the Fe/TaO layer, Fe/Ta1 and Fe/Ta3 cations are coordinated by six oxygen atoms, forming irregular octahedral interconnected into a hexagonal tungsten bronze (HTB) type network. The HTB layer is a fundamental framework in the pyrohlore-related structure.Figure optionsDownload as PowerPoint slideHighlights
► Pyrochlore-related compound Sm2FeTaO7 prepared by solid state reaction and sol–gel.
► Sm2FeTaO7 crystallizes with a monoclinic crystal structure and space group C2/c.
► The compound is synthesized by sol–gel at lower temperature and time than solid state.
► Surface area of sol–gel Sm2FeTaO7 is 10 times higher than that prepared by solid state.