Novel Mixed Cobalt/Chromium Phosphate NaCoCr₂(PO₄)₃ Showing Spin-Flop Transition

Abstract

We describe the synthesis and the crystallographic and magnetic properties of a novel NaCoCr2(PO4)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 α-CrPO4-type structure in space group Imma with the following unit cell parameters: a = 10.413(1) Å; b = 13.027(1) Å; c = 6.372(1) Å. The framework consists of PO4 tetrahedra, M(1)O6 (M(1) = Cr) octahedra, and M(2)2O10 (M(2) = 0.5Cr+0.5Co) binuclear unit of edge-sharing MO6 octahedra. It can be described in terms of two building blocks: sheets consisting of corner-sharing M(2)2O10 units with PO4 tetrahedra found parallel to the (b,c) plane, and chains made by corner-sharing CrO6 octahedra and PO4 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 α-CrPO4-type structure considering a positive charge balance according to the equation Cr(3+) → Co(2+) + Na(+), resulting in sodium countercation introduction within the unoccupied channels shown in the α-CrPO4 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.

Structural and Spectroscopic Studies of NaCuCr2(PO4)3: A Noncentrosymmetric Phosphate Belonging to the α-CrPO4-Type Compounds

“…First, the superposed NPD patterns showed peaks splitting around 35°and 80°and 117°( see enlarged parts in the top of Figure 1). 7,10,15 However, when a standard Shannon ionic radius of 0.73 Å is considered for Cu 2+ , the (202) peak positions for NaCuP clearly do not support such Vegard law, but rather a high contraction cell along (010) planes, leading to symmetry lowering, induced by an expected Jahn−Tellertype distortion for Cu 2+ cations. 30 Finally, when a lower symmetry was taken, the new peak appearing around 35°was indexed with a (hkl) reflection which is systematically absent for Imma symmetry (see the enlarged part in Figure 1 and Figure SI2c).…”

“…This work sheds light on a slight but important structural modification with respect to the Imma α-CrPO 4 -type structure exemplified by NaMCr 2 (PO 4 ) 3 (NaMP) (M = Co, Ni) compounds. 7,10 The Imma to Imm2 phase modification when Cu introduced is also supported by IR and Raman spectroscopic investigations. This mixture was dissolved in an aqueous acid solution, stirred continuously, then air-dried overnight in an oven at 353 K to evaporate the water.…”

“…They are related to the α-CrPO 4 -type structure and belong to the Na 2 O-M II O-Cr 2 O 3 -P 2 O 5 systems where M is a divalent transition-metal cation. Among other experimental results, a spin flop transition at 32 K in the NaCoCr 2 (PO 4 ) 3 compound due to the magnetic superexchange interaction competitions was reported as well as stepped magnetization in mixed-Fe 2+ /Fe 3+ phosphates. , …”

“…They are identified with the general chemical formula □ 3 M 3 (XO 4 ) 3 , where □ is a vacancy that can be filled by monovalent and/or divalent cations, introducing an oxidation state decrease of the transition metal M and XO 4 referring to tetrahedral entity, respectively. They all crystallize with a centrosymmetric Imma space group. − Interestingly, some of them with the following general formula A 2 M 2+ 2 M 3+ (PO 4 ) 3 , where A is an alkali and M are metals able to show an oxidation equal to 2 and/or 3, were recently described as low-temperature polymorphs of the alluaudite-type structure. , …”

K1+2xNi1−xFe2(AsO4)3(x= 0,125): un nouvel arséniate à structure de type α-CrPO4

“…Notes: DNP = diffraction des neutrons sur poudre; DRXM = diffraction des rayons X sur moncristal; DRXP = diffraction des rayons X sur poudre; & = site vacant. Ré férences: (a) Glaum et al les deux exclusivement par des cations trivalents (Rittner & Glaum, 1994;Attfield et al, 1989), par une distribution statistique de cations di-et trivalents (Yahia et al, 2016;Souiwa et al, 2015b;Essehli et al, 2015), l'un par une ré partition statistique de cations di-et trivalents et l'autre uniquement par des cations di-ou trivalents (Souiwa et al, 2015a; Ben Smail & Zid, 2017b) ou l'un par des cations divalents et l'autre par des cations trivalents (Bouraima et al, 2016;Ouaatta et al, 2015;Alhakmi et al, 2013a,b;Assani et al, 2013;Korzenski et al, 1999;Hidouri et al, 2004;Kinomura et al, 1989). La derniè re ré partition cationique est observé e dans l'arsé niate objet de ce travail.…”