As can be seen from Fig. , the dependence of the lattice parameter of the cubic solid solution on the ZnO content is not linear, i.e. the Vegard's law is not fulfilled for the FeO-ZnO system, in contrast to other binary and ternary cubic solid solutions such as NiO-ZnO , MnO-ZnO , LiFeO 2 -ZnO and LiScO 2 -ZnO . This is not surprising for iron (II) oxide since, unlike the other oxides mentioned above, the lattice parameter of "FeO" (wüstite) varies within wide (from 4.29 to 4.33 Å) ranges depending on stoichiometry and preparation method . Nevertheless, on a qualitative level, this dependence is in agreement with the results of the previous work , which reported a non-monotonic behavior of the lattice parameter for the cubic solid solution in the FeO-ZnO system, albeit in a narrower concentration range (x ≤ 0.25). The lattice parameter values are scattered somewhat erratically between 4.28 Å for rs-ZnO and any value known from the literature for rs-FeO . In general, the dependence of the lattice parameter on the composition of cubic FeO-ZnO solid solution can be characterized by three regions: x ≤ 0.2, 0.2 ≤ x ≤ 0.5, and x ≥ 0.5, within the limits of which this dependence can be considered almost linear.