Structural characterization of YV(4)O(8): simultaneous analysis of coexisting polytypes and simulation of diffuse scattering for a stacking disorder model

The structure of a crystal of newly synthesized YV(4)O(8) was refined on the assumption that two polytypes and their respective twin forms intergrow. The model was expressed as a commensurate composite crystal with two types of subsystem: one is a V(4)O(8) framework with rather large tunnels and the other consists of Y ions. In the tunnels, Y ions and vacancies are located at every second site in an ordered manner that is characteristic of each polytype. Refinement was performed using a high-dimensional formalism and all reflections from all domains. Diffuse streaks observed in the X-ray and electron diffraction patterns were simulated using the matrix method that has been used for one-dimensional disorder such as stacking faults. The unusual diffraction phenomena that occur in a crystal of YV(4)O(8) are explained as arising from a multiple-domain structure of coexisting polytypes.