Variation of large-scale regularity in modulated structures of Ca2CoSi2O7 studied by a simulation method

The period of two‐dimensional modulation in Ca2CoSi2O7 varies with temperature (q = 0.285–1/3). The change in the modulated structure with the variation of q has been clarified by the construction of the structures using various q values and the modulation amplitudes determined at 293 K [q = 0.2913 (1), tetragonal]. The features of the modulated structures are characterized by the formation of CaO6 polyhedra and the variable distribution of bundles along the c‐axis, composed of four arrays of CaO6 polyhedra and an array of CoO4 tetrahedra. The formation of octagonal arrangements of the bundles is a typical feature of the structures in the incommensurate phase. Large‐scale regularities with sizes much larger than the modulation wavelength are also formed in the structures.