Temperature dependent lattice distortion in aerogel-produced Fe–Mo oxides

Abstract

Mössbauer studies have been made to evaluate the temperature dependence of lattice distortion in two aerogel-synthesized iron-molybdenum oxides having different atomic ratios $\mathrm{Fe}:\mathrm{Mo}=1:1$ and 2:3, but both with a $\beta \text{-}\mathrm{Fe}\mathrm{Mo}{\mathrm{O}}_4$ structure. The experimentally obtained spectra discern three distinctive iron ions, ${}_{\mathrm{O}}\mathrm{Fe}^{2+}$ , ${}_{\mathrm{PT}}\mathrm{Fe}^{2+}$ , and ${}_{\mathrm{O}∕\mathrm{T}}\mathrm{Fe}^{3+}$ . 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 ${}_{\mathrm{PT}}\mathrm{Fe}^{2+}$ QS indicates a temperature induced asymmetric lattice distortion on the pseudotetrahedral sites.