Novel Mixed Cobalt/Chromium Phosphate NaCoCr sub(2)(PO sub(4)) sub(3) Showing Spin-Flop Transition

We describe the synthesis and the crystallographic and magnetic properties of a novel NaCoCr sub(2)(PO sub(4)) sub(3) phosphate. A conventional solid-state reaction was used to obtain single-phase powders. A Rietveld analysis of powder X-ray diffraction data proposes an orthorhombic symmetry similar...

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Bibliographic Details
Published in:Inorganic chemistry 2015-08, Vol.54 (15), p.7345-7352
Main Authors: Souiwa, Khalifa, Chennabasappa, Madhu, Decourt, Rodolphe, Amara, Mongi Ben, Hidouri, Mourad, Toulemonde, Olivier
Format: Article
Language:English
Subjects:
Channels
Chromium
Mathematical analysis
Order disorder
Phosphates
Sodium
Three dimensional
Unit cell
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Summary:We describe the synthesis and the crystallographic and magnetic properties of a novel NaCoCr sub(2)(PO sub(4)) sub(3) phosphate. A conventional solid-state reaction was used to obtain single-phase powders. A Rietveld analysis of powder X-ray diffraction data proposes an orthorhombic symmetry similar to alpha -CrPO sub(4)-type structure in space group Imma with the following unit cell parameters: a = 10.413(1) [Angstrom]; b = 13.027(1) [Angstrom]; c = 6.372(1) [Angstrom]. The framework consists of PO sub(4) tetrahedra, M(1)O sub(6) (M(1) = Cr) octahedra, and M(2) sub(2)O sub(10) (M(2) = 0.5Cr+0.5Co) binuclear unit of edge-sharing MO sub(6) octahedra. It can be described in terms of two building blocks: sheets consisting of corner-sharing M(2) sub(2)O sub(10) units with PO sub(4) tetrahedra found parallel to the (b,c) plane, and chains made by corner-sharing CrO sub(6) octahedra and PO sub(4) tetrahedra running along the b axis. From the interconnection of the sheets and chains, a 3D rigid skeleton is formed, exhibiting two kinds of intersecting tunnel channels containing the Na+ ions. The proposed structure derives from the alpha -CrPO sub(4)-type structure considering a positive charge balance according to the equation Cr super(3+) arrow right Co super(2+) + Na+, resulting in sodium countercation introduction within the unoccupied channels shown in the alpha -CrPO sub(4) framework. Temperature-dependent DC and AC magnetic susceptibility is indicative of a long-range magnetic ordering occurring at 32 K. Further, spin-flop transition sheds light on a chromium-based phosphate for the first time.
ISSN:0020-1669
DOI:10.1021/acs.inorgchem.5b00776