Mourad Hidouri

Reinvestigation of the binary diagram Na3PO4–FePO4 and crystal structure of a new iron phosphate Na3Fe3(PO4)4

A new iron(III) phosphate Na{sub 3}Fe{sub 3}(PO{sub 4}){sub 4} has been synthesized and characterized. It decomposes before melting at 860 deg. C into FePO{sub 4} and Na{sub 3}Fe{sub 2}(PO{sub 4}){sub 3}. The structure of the compound was determined by single-crystal X-ray diffraction. The unit cell is monoclinic with the following parameters: a=19.601(8) A, b=6.387(1) A, c=10.575(6) A and {beta}=91.81(4) deg.; Z=4; space group: C2/c. Na{sub 3}Fe{sub 3}(PO{sub 4}){sub 4} exhibits a layered structure involving corner-linkage between FeO{sub 6} octahedra, and corner- and edge-sharing between FeO{sub 6} octahedra and PO{sub 4} tetrahedra. The Na{sup +} cations occupying the interlayer space are six- and seven-fold coordinated by oxygen atoms. The relationship between the structure of Na{sub 3}Fe{sub 3}(PO{sub 4}){sub 4} and the previous reported hydrate K{sub 3}Fe{sub 3}(PO{sub 4}){sub 4}{center_dot}H{sub 2}O will be discussed.

Crystal structure, magnetic properties and Mössbauer spectroscopy of NaCaFe3(PO4)4

Abstract A new sodium and calcium iron phosphate, NaCaFe 3 (PO 4 ) 4 , has been synthesized by a flux method and characterized by single crystal X-ray diffraction, magnetic susceptibility and Mossbauer spectroscopy. The compound crystallizes in the orthorhombic space group Pcab with the parameters a =8.706(4) A, b =9.410(1) A, c =29.211(6) A, V =2393 A 3 and Z =8. The structure consists of discrete FeO 6 octahedra and FeO 5 trigonal bipyramids, corner-sharing with PO 4 tetrahedra that form a [Fe 3 P 4 O 16 ] n three-dimensional framework with two distinct cavities which are the Na + and Ca 2+ sites. Mossbauer spectroscopy results confirm those obtained from X-ray diffraction. Magnetic susceptibility indicates an antiferromagnetic behavior with a Neel temperature T N ≈26 K.

Na2BaMg(PO4)2: synthesis, crystal structure and europium photoluminescence properties

Na2BaMg(PO4)2 was synthesized and characterized by X-ray diffraction, differential thermal analysis (DTA), 31P NMR spectroscopy and photoluminescence measurements. This compound crystallized in the P 3¯m1 space group of the trigonal system with the parameters of equivalent hexagonal cell a=0.5305(1) nm and c=0.6986(3) nm. The structure showed a perfect isotipysm with the mineral glaserite K3Na(SO4)2. Thus, it exhibited a lamellar framework which could be described as the stacking along the [001] direction of [MgP2O84−]∞ layers of corner sharing MgO6 polyhedra and PO4 tetrahedra. The Ba2+ cations were located within the interlayer space, while the Na+ ones were found in large cavities bound to the layers. The DTA analysis showed that this compound melt congruently at 1385 K. The 31P NMR spectrum was consistent with the presence of a single phosphorus site in the structure. Optical properties were investigated for the 5% doped Eu3+ and Eu2+ phases. The trivalent europium was used as a local probe, replacing barium while the divalent europium was used to examine whether this material could be used as an optical applications.

Synthesis and structural characterization of a new yttrium phosphate: Na2.5Y0.5Mg7(PO4)6 with fillowite-type structure

A new phosphate, Na2.5Y0.5Mg7(PO4)6 was synthesized as single crystals by the flux method and as a powdered sample by the Pechini technique, and investigated by single crystal X-ray diffraction, charge distribution (CD) and 31P NMR spectroscopy. This compound crystallized in the rhombohedral space group R and its equivalent hexagonal cell had the following parameters: a=1.4976(6) nm, c= 4.2599(7) nm, Z= 18. The structure consisted of MgO5, MgO6, YO6, (Na,Y)O8 and NaOx (x=6, 7 and 9) polyhedra which were linked either directly through common corners, edges and faces and by means of the PO4 tetrahedra via common corners and edges, giving rise to a complex three-dimensional framework, similar to that of the fillowite-like structure. The cation distribution was confirmed by charge distribution (CD) calculations and 31P NMR spectroscopy study.

The iron phosphate NaZnFe2(PO4)3

Crystals of sodium zinc diiron(III) triphosphate, NaZnFe(2)(PO(4))(3), have been synthesized and structurally characterized by single-crystal X-ray diffraction. The compound features a new structural type built up from ZnO(6) octahedra, FeO(6) octahedra and FeO(4) tetrahedra, linked together via the corners and edges of PO(4) tetrahedra to form a three-dimensional framework, with tunnels running along [100]. Within these tunnels, Na(+) cations occupy a highly distorted cubic site.

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

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.

K0.53Mn2.37Fe1.24(PO4)3

During an attempt to crystallize potassium manganese diiron phosphate KMnFe2(PO4)3 by the flux method, a new phase, potassium dimanganese iron triphosphate, K0.53Mn2.37Fe1.24(PO4)3, was isolated. This phase, whose composition was confirmed by ICP analysis, is isotypic with the alluaudite-like phosphates, thus it exhibits the (A2)(A′2)(A1)(A′1)(A′′1)(M1)(M2)2(PO4)3 general formula. The site occupancies led to the following cation distribution: 0.53 K on A′2 (site symmetry 2), 0.31 Mn on A′′1, 1.0 Mn on M1 (site symmetry 2) and (0.62 Fe + 0.38 Mn) on M2. The structure is built up from infinite chains of edge-sharing M1O6 and M2O6 octahedra. These chains run along [10] and are connected by two different PO4 tetrahedra, one of which exhibits 2 symmetry. The resulting three-dimensional framework delimits large tunnels parallel to [001], which are partially occupied by the K+ and Mn2+ cations.

The iron phosphate K3Fe5(PO4)6

The crystal structure of tripotassium pentairon hexaphosphate has been determined by single-crystal X-ray diffraction. The structure contains one Fe atom on a center of symmetry, one K, two Fe and two P atoms on twofold axes, and one Fe, two P and one K atom in general positions. The K(3)Fe(5)(PO(4))(6) structure consists of a complex three-dimensional framework of corner-sharing between iron polyhedra, and corner- and edge-sharing between PO(4) tetrahedra and iron polyhedra (FeO(5) and FeO(6)). This linkage between iron and phosphorus forms intersecting channels containing the K atoms.

RbCuFe(PO4)2.

A new iron phosphate, rubidium copper(II) iron(III) bis(phosphate), RbCuFe(PO4)2, has been synthesized as single crystals by the flux method. This compound is isostructural with KCuFe(PO4)2 [Badri et al. (2011 ▶), J. Solid State Chem. 184, 937–944]. Its structure is built up from Cu2O8 units of edge-sharing CuO5 polyhedra, interconnected by FeO6 octahedra through common corners to form undulating chains that extend infinitely along the [011] and [01-1] directions. The linkage of such chains is ensured by the PO4 tetraedra and the resulting three-dimensional framework forms quasi-elliptic tunnels parallel to the [101] direction in which the Rb+ cations are located.

The iron phosphate CaFe3(PO4)3O

A new iron phosphate, calcium triiron(III) tris(phosphate) oxide, CaFe3(PO4)3O, has been isolated and shown to exhibit a three-dimensional structure built by FeO6 octahedra, FeO5 trigonal bipyramids and PO4 tetrahedra. The FeOx (x = 5, 6) polyhedra are linked through common corners and edges, forming [Fe6O28]∞ chains with branches running along [010]. Adjacent chains are connected by the phosphate groups via common corners and edges, giving rise to a three-dimensional framework analogous to those of the previously reported SrFe3(PO4)3O and Bi0.4Fe3(PO4)3O structures, in which the Ca2+ cations occupy a single symmetry non-equivalent cavity.