TY - JOUR

T1 - Halide-sodalites

T2 - thermal behavior at low temperatures and local deviations from the average structure

AU - Wolpmann, Marius

AU - Etter, Martin

AU - Kirsch, Andrea

AU - Balzaretti, Filippo

AU - Dononelli, Wilke

AU - Robben, Lars

AU - Gesing, Thorsten M.

N1 - Funding Information: We gratefully acknowledge the Deutsche Forschungsgemeinschaft (DFG) for financial support through RO5995/2-1 and within the large instrument program (INST 144/335-1 FUGG Raman spectrometer, INST 144/435-1 FUGG TD X-ray powder diffractometer and INST 144/458-1 FUGG Std. X-ray powder diffractometer). We also acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at PETRA III beamlines P02.1 and P21.1. We would like to thank Dr. Soham Banerjee for assistance in using beamline P21.1. Beamtime was allocated for proposals I-20200180 and I-20200535. AK would like to thank Niels Lefeld and Mathias Gogolin for beamtime assistance. Funding Information: Research funding: This work was funded by Deutsche Forschungsgemeinschaft (DFG) (RO5995/2-1). Publisher Copyright: © 2022 Walter de Gruyter GmbH, Berlin/Boston.

PY - 2022

Y1 - 2022

N2 - Sodalites of the general type |Na8X2|[T1T2O4]6 with X = Cl-, Br-, I- have been synthesized for Al-Si, Ga-Si, Al-Ge and Ga-Ge as T1-T2 frameworks. The structures were examined using in-house and synchrotron X-ray diffraction, Raman spectroscopy, force-field structure optimizations and DFT based ab-initio molecular dynamics (MD) computations. Calculated phonon density of states (PDOS) of the 12 compounds show only minor differences within a framework composition with a lowering of certain phonon energies with increasing anion size. Earlier published Debye and Einstein temperatures obtained with a Debye-Einstein-anharmonicity (DEA) model approach are confirmed using the determined low-temperature lattice parameters (18 K-293 K) and show no correlation with the respective PDOS. Small-box refinements against radial pair distribution functions (PDF) allowed the determination of anisotropic displacement ellipsoids (ADP) for Na+ and O2-, indicating a strong dependency of the ADP of Na+ on the chemical composition. Significantly lower thermal displacements from MD calculations suggested an influence of structural displacements. For compounds with an aspherical ADP for sodium, structural models could be refined in which the sodium is located on two 8e or one 24i site (both partially occupied), and also temperature-dependent (100 K-300 K) for the compounds with Ga-Ge framework. 3D-plots of the bond-valence sums of Na+ further validate the structural differences. These results imply that the local structure of halide-sodalites in many cases is not best described by the known average structure and may even not be cubic.

AB - Sodalites of the general type |Na8X2|[T1T2O4]6 with X = Cl-, Br-, I- have been synthesized for Al-Si, Ga-Si, Al-Ge and Ga-Ge as T1-T2 frameworks. The structures were examined using in-house and synchrotron X-ray diffraction, Raman spectroscopy, force-field structure optimizations and DFT based ab-initio molecular dynamics (MD) computations. Calculated phonon density of states (PDOS) of the 12 compounds show only minor differences within a framework composition with a lowering of certain phonon energies with increasing anion size. Earlier published Debye and Einstein temperatures obtained with a Debye-Einstein-anharmonicity (DEA) model approach are confirmed using the determined low-temperature lattice parameters (18 K-293 K) and show no correlation with the respective PDOS. Small-box refinements against radial pair distribution functions (PDF) allowed the determination of anisotropic displacement ellipsoids (ADP) for Na+ and O2-, indicating a strong dependency of the ADP of Na+ on the chemical composition. Significantly lower thermal displacements from MD calculations suggested an influence of structural displacements. For compounds with an aspherical ADP for sodium, structural models could be refined in which the sodium is located on two 8e or one 24i site (both partially occupied), and also temperature-dependent (100 K-300 K) for the compounds with Ga-Ge framework. 3D-plots of the bond-valence sums of Na+ further validate the structural differences. These results imply that the local structure of halide-sodalites in many cases is not best described by the known average structure and may even not be cubic.

KW - GULP

KW - molecular dynamics

KW - sodalite

KW - total scattering

U2 - 10.1515/zkri-2022-0037

DO - 10.1515/zkri-2022-0037

M3 - Journal article

AN - SCOPUS:85141286817

VL - 238

SP - 27

EP - 38

JO - Zeitschfrift fur Kristallographie

JF - Zeitschfrift fur Kristallographie

SN - 2194-4946

IS - 1-2

ER -