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Modulated anharmonic ADPs are intrinsic to aperiodic crystals : a case study on incommensurate Rb₂ZnCl₄

Title data

Li, Liang ; Wölfel, Andreas ; Mondal, Swastik ; Schreurs, Antoine M. M. ; Kroon-Batenburg, Loes M. J. ; van Smaalen, Sander ; Schönleber, Andreas:
Modulated anharmonic ADPs are intrinsic to aperiodic crystals : a case study on incommensurate Rb₂ZnCl₄.
In: Acta Crystallographica Section B. Vol. 67 (2011) Issue 3 . - pp. 205-217.
ISSN 2052-5206
DOI: https://doi.org/10.1107/S0108768111013814

Official URL: Volltext

Project information

Project financing: Deutsche Forschungsgemeinschaft

Abstract in another language

A combination of structure refinements, analysis of the superspace MEM density and interpretation of difference-Fourier maps has been used to characterize the incommensurate modulation of rubidium tetrachlorozincate, Rb2ZnCl4, at a temperature of T = 196 K, close to the lock-in transition at Tlock-in = 192 K. The modulation is found to consist of a combination of displacement modulation functions, modulated atomic displacement parameters (ADPs) and modulated third-order anharmonic ADPs. Up to fifth-order Fourier coefficients could be refined against diffraction data containing up to fifth-order satellite reflections. The center-of-charge of the atomic basins of the MEM density and the displacive modulation functions of the structure model provide equivalent descriptions of the displacive modulation. Modulations of the ADPs and anharmonic ADPs are visible in the MEM density, but extracting quantitative information about these modulations appears to be difficult. In the structure refinements the modulation parameters of the ADPs form a dependent set, and ad hoc restrictions had to be introduced in the refinements. It is suggested that modulated harmonic ADPs and modulated third-order anharmonic ADPs form an intrinsic part, however small, of incommensurately modulated structures in general. Refinements of alternate models with and without parameters for modulated ADPs lead to significant differences between the parameters of the displacement modulation in these two types of models, thus showing the modulation of ADPs to be important for a correct description of the displacive modulation. The resulting functions do not provide evidence for an interpretation of the modulation by a soliton model.

Further data

Item Type: Article in a journal
Refereed: Yes
Keywords: aperiodic crystals; incommensurate modulated structures; MEM density; ADPs
Institutions of the University: Faculties > Faculty of Mathematics, Physics und Computer Science > Group Material Sciences > Chair Crystallography > Chair Crystallography - Univ.-Prof. Dr. Sander van Smaalen
Faculties
Faculties > Faculty of Mathematics, Physics und Computer Science
Faculties > Faculty of Mathematics, Physics und Computer Science > Group Material Sciences
Faculties > Faculty of Mathematics, Physics und Computer Science > Group Material Sciences > Chair Crystallography
Result of work at the UBT: Yes
DDC Subjects: 500 Science > 530 Physics
Date Deposited: 30 Jul 2015 09:12
Last Modified: 14 Jun 2016 05:36
URI: https://eref.uni-bayreuth.de/id/eprint/17438