Exploiting superspace to clarify vacancy and Al/Si ordering in mullite.

ABSTRACT: Synchrotron single-crystal X-ray diffraction has revealed diffuse scattering alongside sharp satellite reflections for different samples of mullite (Al_4+2x Si_2-2x O_10-x ). Structural models have been developed in (3+1)-dimensional superspace that account for vacancy ordering and Al/Si ordering based on harmonic modulation functions. A constraint scheme is presented which explains the crystal-chemical relationships between the split sites of the average structure. The modulation amplitudes of the refinements differ significantly by a factor of ∼3, which is explained in terms of different degrees of ordering, i.e. vacancies follow the same ordering principle in all samples but to different extents. A new approach is applied for the

SUBMITTER: Klar PB 

PROVIDER: S-EPMC6038955 | biostudies-literature | 2018 Jul

REPOSITORIES: biostudies-literature