For compositions x = 0.1 and x = 0 (pure MnO), the cubic phase is stable up to 1050 K inclusive; no lines of wurtzite phase appear, and only weak lines of higher manganese oxides to Mn 2+ doping of 30-35 mol% . Note that the equilibrium solubility of Mn 2+ in w-ZnO for this system is not more than 25% . A higher value (up to 35 mol%) has so far only been observed for thin films . Thus, as in the case of the CoO-ZnO system, heating of metastable cubic solid solutions results in formation of highly supersaturated Mn 2+ solid solutions with wurtzite structure.