Thus, is it consistent but somewhat coincidental that block size trends with slope in the Nb2O5-WO3 family; TiO2-Nb2O5 exhibits the opposite trend and block size decreases as the degree of cation mixing and increase when the ratio of Ti/Nb increases. The coherence of the intermediate-voltage phase transition, and the zero-expansion behavior, are uniquely exemplified in NaNb7O18.