Symmetry mode based parametric Rietveld refinement of the structural phase transition of CuInSe2

Symmetry modes provide an alternative method to describe crystal structures. Using the fact that many crystal structures can be described as a distorted version of a higher symmetric parent structure, the traditional atomic positions, occupancies or lattice parameters are no longer used. Instead, all structural features are described applying symmetry modes. This can be of particular interest if structural changes during a real phase transition are studied. The symmetry modes of one given type belonging to the same irreducible representation (irrep) comprise an order parameter. The decomposition of a crystal structure in terms of symmetry modes can nowadays be done using webbased software programs like ISODISTORT (http://stokes.byu.edu/isodistort.html) or AMPLIMODES (http://www.cryst.ehu.es/cryst/amplimodes.html)