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Three isostructural chromium phosphates, Na 1+ x Mg 1+ x Cr 2− x (PO 4 ) 3 with x = 0 ( I ) and 0.2 ( II ), and NaZnCr 2 (PO 4 ) 3 ( III ) have been synthesized for the first time. Their analysis by single and powder X-ray diffraction techniques showed that they crystallize in the orthorhombic system with space group Imma . The structure is closely related to that of the α-CrPO 4 type with one main feature being a disorder, in the studied compounds, between the Cr 3+ and M 2+ (M = Mg or Zn) cations. The 3D framework is built up by PO 4 tetrahedra, M(1)O 6 octahedra and M(2) 2 O 10 bioctahedral units of edge sharing octahedra, linked through common corners and edges. This framework delimits interesting tunnels in which the Na + cations are located. The observed bands in the FT-IR spectra for I and III were assigned to corresponding vibrations of the PO 4 tetrahedra. The EPR spectra exhibit two different resonance lines S1 and S2, characteristic of octahedral Cr 3+ ions. The thermal evolution of EPR integral intensities of these signals were assigned to antiferromagnetic (AFM) coupling between nearest neighbors Cr 3+ ions. The AFM ordering within these compounds at low temperature was also revealed from the thermal dependence of the molar magnetic susceptibility. At high temperature, a deviation from the Curie–Weiss law is observed and it was attributed to a magnetic frustration phenomenon. [ABSTRACT FROM AUTHOR]

Highlights: [•] This study reports the synthesis and characterization of a new iron phosphate. [•] The cationic distribution is supported by a Mössbauer spectroscopy study. [•] The magnetic susceptibility results are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Na2Mn2(1− x)Cd2x Fe(PO4)3 (0≤ x ≤1) phosphates were prepared by solid state reaction and characterized by powder X-ray diffraction, magnetic susceptibility and Mössbauer spectroscopy. The X-ray diffraction patterns indicated the formation of a continuous solid solution which crystallizes in the alluaudite structural type characterized by the general formula X(2)X(1)M(1)M(2)2(PO4)3. The cation distribution, deduced from a structure refinement of the x =0, 0.5 and 1 compositions, is ordered in the X(2) sites and disordered in the remaining X(1), M(1) and M(2) sites. The magnetic susceptibility study revealed an antiferromagnetic behaviour of the studied compounds. The 57Fe Mössbauer spectroscopy confirmed the structural results and proved the exclusive presence of Fe3+ ions. [Copyright &y& Elsevier]

Abstract: Synthesis, single crystal X-ray diffraction, Mössbauer and magnetic studies of a new iron phosphate Rb9Fe7(PO4)10 are described. This compound crystallizes in the monoclinic system with the space group P21/a and the following parameters: a =9.886(4)Å, b =16.493(2)Å, c =13.437(2)Å, β =110.49(3)° and Z =2. Its structure is closely related to that of the Cs9−x K x Fe7(PO4)10 phosphates. The 3D framework consists of FeO6 and FeO5 polyhedra and Fe2O10 units of corner-sharing FeO6 and FeO5 polyhedra. These units are linked to each other by the phosphate tetrahedra in such a way that the resulting framework forms large intersecting tunnels extending along the a and c directions, where the Rb+ cations are located. A high temperature X-ray powder diffraction study showed a partial decomposition of the product above 773K. The magnetic susceptibility results are consistent with Fe(III) showing an antiferromagnetic ordering below T N ≈19K and a paramagnetic behavior in the range of 50–300K. The application of the Curie–Weiss law yields an effective moment of 5.99μB in a good agreement with the ideal spin only value of 5.92μB for d5-iron(III). The distribution of iron and its local environments were confirmed by a Mössbauer study undertaken at 293 and 4.2K. [Copyright &y& Elsevier]

Abstract: A new iron oxophosphate of composition Rb7Fe7(PO4)8O2·2H2O has been synthesized and studied by X-ray diffraction, TG and DTA analysis, magnetic susceptibility, neutron diffraction, Mössbauer spectroscopy and ionic conductivity. This compound crystallizes in the monoclinic system with the P21/c space group and the unit cell parameters a =8.224(8)Å, b =22.162(6)Å, c =9.962(6)Å and β =109.41(8)°. Its structure is built up from Fe7O32 clusters of edge- and corner-sharing FeO5 and FeO6 polyhedra. Neighboring clusters are connected by the phosphate tetrahedra to form a three-dimensional framework. The Rb+ cations and the water molecules are occupying intersecting tunnels parallel to a and c. The presence of water molecules was confirmed by TG and DTA analysis. The magnetic susceptibility measurements have shown the existence of antiferromagnetic ordering below 22K with a weak ferromagnetic component. Additionally, these measurements show evidence for a strong magnetic frustration characterized by |θ/T N|≈12. Powder neutron diffraction study confirms the presence of a long range antiferromagnetic order coupled to a weak ferromagnetic component along the b-axis. The strongly reduced magnetic moments extracted from the refinement support the existence of a magnetically frustrated ground state. The Mössbauer spectroscopy results confirmed the presence of only Fe3+ ions in both five and six coordination. The ionic conductivity measurements led to activation energy of 0.81eV, a value that agrees with the obtained for other rubidium phosphates. [ABSTRACT FROM AUTHOR]

Abstract: A new iron phosphate, KMgFe(PO4)2 has been synthesized and investigated by X-ray diffraction, Mössbauer spectroscopy and ionic conductivity. This compound crystallizes in the monoclinic space group C2/c with the parameters a =18.529(7)Å, b =5.402(3)Å, c =9.374(9)Å, β =120.64(5)° and Z =4. Its original structure can be described as the stacking along the [101] direction of [MgFe(PO4)− 2]∞ layers of corner-sharing MO4 (M=0.5 Fe+0.5Mg) and PO4 tetrahedra. The K+ ions are occupying the inter-layer space. The Mössbauer spectroscopy confirms the occurrence of only tetrahedral Fe3+ ions and gives a definitive proof of the disordered character of their distribution. Ionic conductivity results obtained by the impedance spectroscopy technique show that this material is a two-dimensional ionic conductor, with low activation energy, 0.51eV, that is interpreted on the basis of two-dimensional pathways. [Copyright &y& Elsevier]

Abstract: A new iron phosphate K4MgFe3(PO4)5 has been synthesized by the flux method and characterized by single-crystal X-ray diffraction and Mössbauer spectroscopy. It crystallizes in the tetragonal system with the space group and the unit cell parameters a=9.714(3)Å and c=9.494(5)Å. The crystal structure is of a new type. It exhibits a three-dimensional framework built up from corner-sharing MO5 (M=0.75Fe+0.25Mg) trigonal bipyramids and PO4 tetrahedra. The K+ ions are occupying large eight-sided tunnels running along c. A room temperature Mössbauer study confirmed the +3 valence state of iron and its five-coordination. [Copyright &y& Elsevier]

Abstract: Single crystals of a new mixed-valent iron phosphate Na1/2Cu4/3Fe2(PO4)3 have been synthesized by a flux method and structurally characterized from X-ray diffraction data. Crystal data: space group ; ; ; ; ; ; ; ; ; . The three-dimensional structure was found to be closely related to that of the well known Howardevansite structural type. It results from infinite chains of CuO5 and FeO6 polyhedra, joined together by (Cu,□)O6 octahedra and PO4 tetrahedra by corner-sharing. The large cavities in framework are occupied by Na+ ions. The magnetic susceptibility study revealed an antiferromagnetic behavior with Neel temperature of approximately 40K. The Mössbauer spectroscopy confirmed the presence of iron in both +2 and +3 oxidation states. [Copyright &y& Elsevier]

A single crystal of a new sodium calcium iron (III) phosphate, Na4CaFe4(PO4)6, has been synthesized by a flux method and characterized by X-ray diffraction, Mo¨ssbauer spectroscopy and magnetic susceptibility measurements. The compound crystallizes in the monoclinic space group C2/c(a=12.099(5) A˚, b=12.480(5) A˚, c=6.404(2) A˚, β=113.77(3)°, Z=2, R1=0.022, Rw2=0.066). The crystal structure belongs to the alluaudite type, characterized by the X(2)X(1)M(1)M(2)2(PO4)3 general formula. The open framework results from Fe2O10 units of edge-sharing FeO6 octahedra, which alternate with M(1)O6 octahedra (M(1)=1/2Na+1/2Na+1/2Ca) that form infinite chains. These chains are linked together through the common corners of PO4 tetrahedra yielding two distinct tunnels of sodium cation occupation. This compound is antiferromagnetic with a Ne´el temperature of 35 K. Mo¨ssbauer parameters are consistent with the structural results. [Copyright &y& Elsevier]