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Topochemical Fluorination of La2NiO4+d: Unprecedented Ordering of Oxide and Fluoride Ions in La2NiO3F2

Wissel, Kerstin and Heldt, Jonas and Groszewicz, Pedro B. and Dasgupta, Supratik and Breitzke, Hergen and Donzelli, Manuel and Waidha, Aamir I. and Fortes, Andrew Dominic and Rohrer, Jochen and Slater, Peter R. and Buntkowsky, Gerd and Clemens, Oliver (2018):
Topochemical Fluorination of La2NiO4+d: Unprecedented Ordering of Oxide and Fluoride Ions in La2NiO3F2.
In: Inorganic Chemistry, ACS Publications, pp. 6549-6560, 57, (11), ISSN 0020-1669, DOI: 10.1021/acs.inorgchem.8b00661, [Online-Edition: https://doi.org/10.1021/acs.inorgchem.8b00661],
[Article]

Abstract

Synopsis

La2NiO3F2 crystallizes in a new anion-ordered distortion variant of the n = 1 Ruddlesden−Popper-type structure. The unprecedented ordering of oxygen anions in the interlayer leads to an expansion of the lattice perpendicular to the stacking direction, accompanied by a strong tilting of NiO4F2 octahedra. A weakening of Ni−F−F−Ni superexchange interactions between the perovskite-type layers due to the reduced covalency of fluoride ions decreases the magnetic ordering temperature strongly.

Abstract The Ruddlesden–Popper (K2NiF4) type phase La2NiO3F2 was prepared via a polymer-based fluorination of La2NiO4+d. The compound was found to crystallize in the orthorhombic space group Cccm (a = 12.8350(4) Å, b = 5.7935(2) Å, c = 5.4864(2) Å). This structural distortion results from an ordered half occupation of the interstitial anion layers and has not been observed previously for K2NiF4-type oxyfluoride compounds. From a combination of neutron and X-ray powder diffraction and 19F magic-angle spinning NMR spectroscopy, it was found that the fluoride ions are only located on the apical anion sites, whereas the oxide ions are located on the interstitial sites. This ordering results in a weakening of the magnetic Ni–F–F–Ni superexchange interactions between the perovskite layers and a reduction of the antiferromagnetic ordering temperature to 49 K. Below 30 K, a small ferromagnetic component was found, which may be the result of a magnetic canting within the antiferromagnetic arrangement and will be the subject of a future low-temperature neutron diffraction study. Additionally, density functional theory-based calculations were performed to further investigate different anion ordering scenarios.

Item Type: Article
Erschienen: 2018
Creators: Wissel, Kerstin and Heldt, Jonas and Groszewicz, Pedro B. and Dasgupta, Supratik and Breitzke, Hergen and Donzelli, Manuel and Waidha, Aamir I. and Fortes, Andrew Dominic and Rohrer, Jochen and Slater, Peter R. and Buntkowsky, Gerd and Clemens, Oliver
Title: Topochemical Fluorination of La2NiO4+d: Unprecedented Ordering of Oxide and Fluoride Ions in La2NiO3F2
Language: English
Abstract:

Synopsis

La2NiO3F2 crystallizes in a new anion-ordered distortion variant of the n = 1 Ruddlesden−Popper-type structure. The unprecedented ordering of oxygen anions in the interlayer leads to an expansion of the lattice perpendicular to the stacking direction, accompanied by a strong tilting of NiO4F2 octahedra. A weakening of Ni−F−F−Ni superexchange interactions between the perovskite-type layers due to the reduced covalency of fluoride ions decreases the magnetic ordering temperature strongly.

Abstract The Ruddlesden–Popper (K2NiF4) type phase La2NiO3F2 was prepared via a polymer-based fluorination of La2NiO4+d. The compound was found to crystallize in the orthorhombic space group Cccm (a = 12.8350(4) Å, b = 5.7935(2) Å, c = 5.4864(2) Å). This structural distortion results from an ordered half occupation of the interstitial anion layers and has not been observed previously for K2NiF4-type oxyfluoride compounds. From a combination of neutron and X-ray powder diffraction and 19F magic-angle spinning NMR spectroscopy, it was found that the fluoride ions are only located on the apical anion sites, whereas the oxide ions are located on the interstitial sites. This ordering results in a weakening of the magnetic Ni–F–F–Ni superexchange interactions between the perovskite layers and a reduction of the antiferromagnetic ordering temperature to 49 K. Below 30 K, a small ferromagnetic component was found, which may be the result of a magnetic canting within the antiferromagnetic arrangement and will be the subject of a future low-temperature neutron diffraction study. Additionally, density functional theory-based calculations were performed to further investigate different anion ordering scenarios.

Journal or Publication Title: Inorganic Chemistry
Volume: 57
Number: 11
Publisher: ACS Publications
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences > Material Science > Advanced Thin Film Technology
11 Department of Materials and Earth Sciences > Material Science > Fachgebiet Materialdesign durch Synthese
11 Department of Materials and Earth Sciences > Material Science > Materials Modelling
07 Department of Chemistry
07 Department of Chemistry > Physical Chemistry
Date Deposited: 11 Dec 2018 15:01
DOI: 10.1021/acs.inorgchem.8b00661
Official URL: https://doi.org/10.1021/acs.inorgchem.8b00661
Funders: his work was funded by the German Research Foundation within the Emmy Noether program (Grant No. CL551/2-1)., Neutron diffraction beam time on HRPD at ISIS was provided by the Science and Technology Facilities Council (No. 1720040)., Computational time was made available at the Lichtenberg-Cluster at TU Darmstadt, Germany.
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