Application of the High-Symmetry Superspace-Group Description to the Refinement of the Lock-In Structure of Rb₂ZnCl₄

The advantages of using the high-symmetry superspace-group description for the refinement of modulated commensurate structures are discussed, using the ferroelectric phase of Rb₂ZnCl₄ as an example. It is shown that the refinement process is faster and easier to handle than when the usual low-symmetry description is used. Through the choice of a common superspace group for the incommensurate and the lock-in structures, a natural physical hierarchy between the structural parameters may be established, allowing an appropriate block separation and thus accounting efficiently for correlations.