Three rock-salt solid solutions (rs-Ni 1-x Zn x O, x = 0.7; x = 0.8; x = 0.5) and initial NiO were selected for the high-temperature synchrotron X-ray diffraction study at ambient pressure. A representative sequence of powder diffraction patterns for the ultimate composition with the maximum ZnO content (Ni 0.2 Zn 0.8 O) collected during stepwise heating is shown in Fig. . At room temperature, only narrow intense symmetrical lines corresponding to the rock-salt (Fm-3m) phase are observed.