However, it should be noted that the XANES (X-ray Absorption Near Edge Structure) spectrum of rs-Fe 0.5 Zn 0.5 O (No. 7) shown in Fig. does not reveal the presence of Fe 3+ in the solid solution. The characteristic Fe 3+ pre-edge peak (its position is marked with an arrow) is not observed. The spectra acquired at different points of the sample are identical to those shown in Fig. , which indicates a high homogeneity of the sample. Thus, the high pressure -high temperature synthesis allows to preserve the initial Fe 2+ oxidation state in the rs-Fe 1-x Zn x O solid solutions. ) solid solutions. According to SEM data, all synthesized solid solutions are dense ceramics with grain sizes ranging from 1 to 20 μm and with a few pores under grain boundaries. On the surface of large grains there are characteristic features, which manifest themselves in two variants: (i) convexities of oval shape with dimensions of about 100×300 nm, and (ii) cavities of the same shape and size. Moreover, these features on the surface of grains are located at approximately the same distance from each other, i.e. one can speak of a certain order of these structural features. However, the nature of these structural features and the mechanism of their formation during high-pressure synthesis (or recovery) of solid solutions have not yet been understood and therefore require separate investigation. When "FeO" (Ruschim) containing Fe 3 O 4 impurity is used as a precursor, single-phase (according to phase analysis by X-ray diffraction) cubic solid solutions (Nos. . It can be assumed that this is a consequence of the formation of small amounts (below the sensitivity limits of the methods used) of ferri-or ferromagnetic impurities. Thus, magnetic measurements are the most direct and sensitive method for determining the presence of ferro-or ferrimagnetic impurities, but do not allow the determination of their origin.