Abstract
A systematic experimental study of the crystal structure, Mössbauer and X-ray photoelectron spectroscopies as well as magnetic measurements were carried out to study the effect of Mo substitution by Nb in the Sr2FeMo1-xNbxO6 compounds with x = 0.5, 0.6, 0.7, 0.8 and 1.0. Rietveld analysis made to the crystal structure indicates that the tetragonal structure is preserved for the compounds with a transition phase from I4/m for x = 0.5, 0.6 and 0.7, to an I4/mcm for x = 0.8 and 1.0 by disorder in the Fe and Mo/Nb cations. Mössbauer spectroscopy showed three different environments around iron. XPS results reveal a mixed oxidation states for Mo6+/5+ ions and a trend to Mo5+ as Nb amount increases. XPS valence band measurements indicate a reduction of the charge carries suggesting a more insulating behavior as Nb content increases. This is reflected in magnetic measurements which show a Ms reduction as consequence of Nb content increases, and a non-reversible behavior between ZFC and FC at low temperatures suggest a spin-glass behavior according to previous works.
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