As starting reagents for the synthesis of FeO-ZnO solid solutions Nos. 1-6 (see Table ), high purity commercially available oxide powders were used: ZnO (Alfa Aesar, 99.99%, 325 mesh) and "FeO" (Aldrich, 99%, 10 mesh). The phase composition of the initial "FeO" is described in detail in Ref. 8; according to our previous estimates it is a rock salt Fe 0.925 O with lattice parameter a = 4.308(1) Å containing ~4 wt% α-Fe, which after high pressure -high temperature treatment transforms into a single-phase wüstite Fe 0.985 O with lattice parameter a = 4.312(1) Å.