The sequence of powder X-ray diffraction patterns for the Mn 0.6 Zn 0.4 O solid solution taken during stepwise heating is shown in Fig. . At room temperature, only narrow, intense and symmetric lines corresponding to the cubic phase are observed. At higher temperatures, the intensities of diffraction lines of the rock-salt phase decrease drastically, while weak and broad reflections of the wurtzite phase appear, indicating the decomposition of the initial single-phase solid solution into a mixture of wurtzite and rock-salt solid solutions.