Mössbauer studies have been made to evaluate the temperature dependence of lattice distortion in two aerogel-synthesized iron-molybdenum oxides having different atomic ratios Fe:Mo=1:1 and 2:3, but both with a β-FeMoO4 structure. The experimentally obtained spectra discern three distinctive iron ions, Fe2+O, Fe2+PT, and Fe3+OT. The subscripts refer to octahedral, pseudotetrahedral, and unresolved octahedral and tetrahedral lattice sites, respectively. As anticipated, only the quadrupole splitting (QS) of both ferrous ions shows a measurable dependence on temperature. However, the remarkable sensitivity of the Fe2+PT QS indicates a temperature induced asymmetric lattice distortion on the pseudotetrahedral sites.

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