Compositionally induced phase transitions and symmetry relations between space groups in the layered system FeIn1−xYxGe2O7

• Published in: Acta crystallographica Section B, Structural science, crystal engineering and materials Structural science, crystal engineering and materials, 2018-08, Vol.74 (4), p.394-402
• Main Authors: Moreno-Tovar, Rosario, Bucio, Lauro, Rosales, Ivonne, Orozco, Eligio
• Format: Article
• Language: English
• Subjects: bond‐valence sum; Cations; Crystallography; Diffraction; Phase transitions; Reduction; Relocation; Rietveld refinement; Structural models; Symmetry; symmetry relations between space groups; thortveitite; Yttrium
• ISSN: 2052-5206; 2052-5192; 2052-5206
• DOI: 10.1107/S2052520618009654

Symmetry reduction in the basic structure of thortveitite‐type compound FeInGe2O7–mC22 (C12/m1, No. 12) promoted by the incorporation of yttrium in the formula FeIn1−xYxGe2O7 gives rise to a derivative structure called thortveitite‐like AA′Ge2O7–mP44, with symmetry described by the space group P121/m1 (No. 11) for x = 0.50, 0.75 and 0.90. The structure remains unchanged within the structural type of thortveitite when x = 0.25. In order to establish structural models for performing a Rietveld refinement to the derivative structure, symmetry relations between space groups connecting the basic and derivative structures were used. The higher contrast to X‐rays of Fe3+, In3+ and Y3+ as well as by the behaviour during the refinements of the isotropic thermal displacements, the values of interatomic distances and calculated bond‐valence sums for each atom in the asymmetric unit, were helpful for elucidating the relocation of cations in the different available crystallographic sites generated by the symmetry reduction. Symmetry relations between space groups for an arrangement before and after a transition in the thortveitite structure were used to build structural models for compositionally induced phase transitions.