It should be noted that for the Ni 0.2 Zn 0.8 O, cubic solid solution with maximum ZnO content, the dependence V(T) is quadratic, whereas for the other compositions it is either linear or quasi-linear (Fig. , Table ). The quadratic dependence V(T) has been previously observed for ZnO-rich cubic solid solutions in other systems . In certain cases, non-linear thermal expansion in oxide systems has been attributed to phase heterogeneity, i.e., the presence of foreign phases .