Journal Article

PUBDB-2025-01658

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Deciphering the commensurately modulated monoclinic phase of Rb$_2$ZnCl$_4$ at low temperatures

Kotla, S. R. (Corresponding author)Extern* ; Ramakrishnan, S.Extern* ; Schaller, A. M.Extern* ; Rekis, T.Extern* ; Eisele, C.Extern* ; Bao, J.-K.Extern* ; Noohinejad, L.Extern*DESY* ; de Laitre, G.Extern*XFEL.EU* ; de Boissieu, M. ; van Smaalen, S. (Corresponding author)Extern*

2025
Academic Press Orlando, Fla.

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Please use a persistent id in citations: doi:10.1016/j.jssc.2025.125226  doi:10.3204/PUBDB-2025-01658

Abstract: The ferroelectric phase III of Rb$_2$ZnCl$_4$ is stable below $T_c$ = 192 K. It is known to be a threefold superstructure of the centrosymmetric high-temperature structure, with space group $P2_1 cn$. Below $T_L$ = 70 K, phase IV exists as a sixfold superstructure. We report the crystal structure of phase IV with monoclinic symmetry $Cc$ (b unique), while a structure model with symmetry $Pn$ (c unique) leads to an almost equally good, yet significantly worse fit to the diffraction data. Employing the superspace approach to these commensurately modulated structures results in modulation waves that follow the two-dimensional irreducible representation $T_1$ of $P2_1 cn$, albeit with different order parameter directions defining $Cc$ and $Pn$ symmetries, consistent with the literature. Standard tools of crystal-chemical analysis indicate that the sixfold superstructure is more stable than the threefold superstructure of phase III. However, crystal-chemical arguments cannot distinguish between the correct superstructure model with space group $Cc$ ($b$ unique) and the incorrect superstructure model with symmetry $Pn$ ($c$ unique) for phase IV. New crystal chemical tools are required, in order to attain a meaningful understanding of superstructure formation.

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Contributing Institute(s):

1. FS DOOR-User (FS DOOR-User)
2. Experimentebetreuung PETRA III (FS-PET-D)

Research Program(s):

1. 631 - Matter – Dynamics, Mechanisms and Control (POF4-631) (POF4-631)
2. 6G3 - PETRA III (DESY) (POF4-6G3) (POF4-6G3)
3. FS-Proposal: I-20190544 (I-20190544) (I-20190544)
4. DFG project G:(GEPRIS)406658237 - Aperiodische Kristalle: Struktur, Dynamik und elektronische Eigenschaften (406658237) (406658237)

Experiment(s):

1. PETRA Beamline P24 (PETRA III)

Appears in the scientific report 2025

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Database coverage:
; ; ; Clarivate Analytics Master Journal List ; Current Contents - Physical, Chemical and Earth Sciences ; Ebsco Academic Search ; Essential Science Indicators ; IF < 5 ; JCR ; Nationallizenz ; SCOPUS ; Science Citation Index Expanded ; Web of Science Core Collection

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