This peculiarity of iron monoxide affects the behavior of its metastable cubic solid solutions under heating. If the decomposition of rs-Fe 1-x Zn x O (0.4 ≤ x ≤ 0.6) solid solutions can be described by the same scheme as for the other systems considered above, i.e., by the formation of two solid solutions (cubic and wurtzite) with the possible presence of a spinel phase due to oxidation (Fig. ), for compositions with high iron content (0.1 ≤ x ≤ 0.3) a weak 101 line of α-Fe appears in the range of 800-1000 K (Fig. ), which disappears at higher temperatures.