Structural disorder, octahedral coordination and two-dimensional ferromagnetism in anhydrous alums

Journal Article · Wed Oct 15 00:00:00 EDT 2008 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2008.07.006· OSTI ID:21212063

Huang, Q ^[1]; Zandbergen, H W ^[2]; McQueen, T M; Cava, R J ^[3]

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1. Center for Neutron Research, The National Institute for Standards and Technology, Gaithersberg, MD (United States)
2. Kavli Institute for Nanoscience, Technical University of Delft, Delft (Netherlands)
3. Frick Laboratory, Department of Chemistry, Princeton University, Room 114, Princeton, NJ 08544 (United States)

The crystal structures of the triangular lattice, layered anhydrous alums KCr(SO{sub 4}){sub 2}, RbCr(SO{sub 4}){sub 2} and KAl(SO{sub 4}){sub 2} are characterized by X-ray and neutron powder diffraction (NPD) at temperatures between 1.4 and 773 K. The compounds all crystallize in the space group P3-bar, with octahedral coordination of the trivalent cations. In all cases, small amounts of disorder in the stacking of the triangular layers of corner sharing MO{sub 6} octahedra and SO{sub 4} tetrahedra is seen, with the MO{sub 6}-SO{sub 4} network rotated in opposite directions between layers. The electron diffraction study of KCr(SO{sub 4}){sub 2} supports this model, which on an average can be taken to imply trigonal prismatic coordination for the M{sup 3+} ions; as was previously reported for the prototype anhydrous alum, KAl(SO{sub 4}){sub 2}. The temperature-dependent magnetic susceptibilities for ACr(SO{sub 4}){sub 2} (A=K, Rb, Cs) indicate the presence of predominantly ferromagnetic interactions. Low-temperature powder neutron diffraction reveals that the magnetic ordering is ferromagnetic in-plane, with antiferromagnetic ordering between planes below 3 K. - Graphical abstract: The anhydrous alums KCr(SO{sub 4}){sub 2}, RbCr(SO{sub 4}){sub 2} and KAl(SO{sub 4}){sub 2} are characterized by X-ray and neutron powder diffraction and TEM diffraction. All compounds have octahedral coordination of the trivalent cations. Stacking disorder is observed, with the MO{sub 6}-SO{sub 4} network of polyhedra rotated in opposite directions between layers. Low-temperature NPD reveals ferromagnetic in-plane ordering, with antiferromagnetic ordering between planes below 3 K.

• OSTI ID: 21212063
• Journal Information: Journal of Solid State Chemistry, Vol. 181, Issue 10; Other Information: DOI: 10.1016/j.jssc.2008.07.006; PII: S0022-4596(08)00377-0; Copyright (c) 2008 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ANTIFERROMAGNETISM
CATIONS
CHROMIUM COMPOUNDS
CRYSTAL STRUCTURE
ELECTRON DIFFRACTION
FERROMAGNETISM
LAYERS
MAGNETIC SUSCEPTIBILITY
MAGNETIZATION
NEUTRON DIFFRACTION
POTASSIUM COMPOUNDS
RUBIDIUM COMPOUNDS
SPACE GROUPS
SULFATES
TEMPERATURE RANGE 0000-0013 K
TRANSMISSION ELECTRON MICROSCOPY
X RADIATION