As starting materials, high-purity powders of wurtzite ZnO (Alfa Aesar, 99.99%, 325 mesh), rocksalt CoO (Aldrich, 99.99%), MnO (Alfa Aesar, 99.99%, 325 mesh), NiO (Prolabo, 99%) and "FeO" (Aldrich, 99%, 10 mesh) have been used. The MeO-ZnO mixtures of various stoichiometries (ZnO molar fraction varied from 0.2 to 1.0 with 0.1 concentration step) were thoroughly ground in an agate mortar under acetone, then pressed into pellets and placed into gold capsules. High-pressure synthesis of solid solutions has been performed at 7.7 GPa and 1450-1650 K using a toroid-type high-pressure apparatus at LSPM-CNRS . Experimental details have been described elsewhere . Single-phase rs-Co 0.3 Zn 0.7 O, rs-Co 0.4 Zn 0.6 O and rs-Fe 0.4 Zn 0.6 O solid solutions have been synthesized by "sodium chloride matrix" method . The mixture of oxides and NaCl (in weight ratio 1:5) has been treated at 7.7 GPa and 1500 K and subsequently quenched down to ambient conditions. The sodium chloride matrix was then carefully washed out with cold water.