We present the temperature dependence of elastic modes of Fe3−xZnxO4 with x = 0, x = 0.02 and x = 0.032. The c44 shear modes show a pronounced softening which can be normalized to a common behavior for all these substances. We can explain the softening with a bilinear coupling of the elastic strain to an order parameter linked to charge ordering processes. The other elastic modes (c11, c12 and the bulk modulus) do not show any softening. We present a symmetry analysis for the charge ordering model.
PACS. 71.30.+h Metal-insulator transitions and other electronic transitions -62.65.+k Acoustical properties of solids -75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)