Atomic Modulation Functions, Periodic Nodal Surfaces and the three-dimensional incommensurately modulated (1-x)Bi2O3 center dot xNb(2)O(5), 0.06 < x < 0.23, solid solution

Superspace group symmetry is used to parameterize the compositional and dis placive degrees of free dom associated with the complex, three-dimensional incommensurately modulated (1-x)Bi2O3. xNb(2)O(5), 0.06 < x < 0.23, type II solid solution. The metal and oxygen ion Atomic Modulation Functions are s hown to be closely related to the so-called D Periodic Nodal Surface. The s tructural consequences of this shape for real three-dimensional physical sp ace are spelt out and used to test the structural plausibility of previousl y proposed structural models.