Thus, rock salt Me 1-x Zn x O solid solutions (Me = Ni 2+ , Co 2+ , Fe 2+ , Mn 2+ ) are kinetically stable at ambient pressure up to 670-1100 K depending on composition and type of Me 2+ cation. With increasing temperature, the phase transformation of the single-phase cubic solid solution Me 1-x Zn x O leads in most cases to a mixture of two solid solutions with cubic and wurtzite structures. For some cubic solid solutions of the CoO-ZnO system, their decomposition can result in formation of a single-phase solid solution with a wurtzite structure. Oxidation of the Me 2+ cation (Co, Mn) by atmospheric oxygen at high temperatures can lead to the formation of mixed higher oxides of these metals. In solid solutions with iron oxide, the formation of magnetite and alpha-iron phases is possible at temperatures of 800-1000 K. In all systems studied, cubic solid solutions with maximum zinc oxide content show a quadratic temperature dependence of thermal expansion. Error bars are smaller than the symbols. Dashed lines are least squares fits (see Table ).