Preparation et etude d'un oxyphosphate Fe4(PO4)2O

This compound is obtained in several ways, at 900°C, from the components of the FePO system when the oxygen pressure is made suitable, or from Fe₃(PO₄)₂ + Fe + Fe₂O₃ in a sealed tube under vacuum. It crystallizes under these latter conditions with a trace of FeCl₂. The cell is monoclinic; a = 6.564(1), b = 11.271(2), c = 9.383(2) Å, β = 103.95 (2)°, with Z = 4, group $\text{P2}{}_1\text{c}$. The structure is determined thanks to the use of a direct method and Fourier synthesis and is refined to R = 0.033. The PO₄ tetrahedra are isolated; the iron fills four crystallographic sites: three are more or less distorted octahedra, the fourth is a trigonal bipyramid. The oxyphosphate character is ascertained by the presence of some oxygen atoms connected to iron only, with, moreover, a low site potential. This compound is paramagnetic above 90°K. Its Mössbauer spectrum exhibits four doublets in good agreement with the structure; in order to identify which one corresponds to the hexahedral site, the phase Fe₃Zn(PO₄)₂O has been prepared, but its Mössbauer spectrum, in spite of the zinc affinity for the V coordination, shows that two sites are modified, which does not allow conclusions to be made.     

In situ Mössbauer spectroscopy studies of the electrochemical reaction of lithium with KFeS2

In situ Mössbauer spectroscopy has been used to study the electrochemical reaction of lithium with KFeS₂. Compositions KLi_xFeS₂ with Δx = 0.25 were obtained by coulometric titration for one complete discharge and recharge. Mössbauer spectra were obtained at each composition. Three new iron sites are identified in addition to Fe³⁺ in KFeS₂. A mechanism to account for the electrochemical and Mössbauer data is proposed. The end product KLiFeS₂ has been synthesized and found to be body-centered tetragonal with a = 3.938(2) Å and c = 13.135(5) Å.     

Etude cristallographique et par effet Mössbauer du fluorure ferrimagnétique Na5Fe3F14γ

The structure of ferrimagnetic γ-Na₅Fe₃F₁₄ has been determined by single-crystal X-ray diffraction. The cell is tetragonal with space group P4₂2₁2 and parameters a = 7.345 ± 0.007 Å and c = 10.400 ± 0.007 Å. The iron atoms occupy a twofold and a fourfold position in the lattice and are octahedrally surrounded by fluorines. These octahedra share corners and form two-dimensional layers of formula (Fe₃F₁₄)^5n?_n. The Mössbauer spectra were measured from 4.2 to 293°K and the results are discussed in terms of the position and environment of iron atoms in the lattice.     

Mössbauer effect study of carbides and silico-carbides. II. (Mn1−xFex)5SiC

The substitution of iron in Mn₅SiC has been studied by Mössbauer spectroscopy at room temperature. The Mn₃ site is the first saturated site while the filling of the Mn₄ site is the most difficult. The magnitude of the quadrupole splittings of iron atoms having two carbon nearest neighbors at a distance close to 2 Å in Fe₃C, Fe₅C₂, Mn₅SiC, and some M₃M′C perovskite carbides in the paramagnetic state are discussed. These quadrupole splittings are practically insensitive to the metallic neighborhood of the sites under consideration. They increase regularly with the angle of the two iron-carbon bonds.     

The crystal structure and magnetic properties of the synthetic langbeinite KBaFe2(PO4)3

Powder neutron diffraction data have been used to refine the crystal structure of KBaFe₂(PO₄)₃ at 4.2 K; space group P2₁3, a₀ = 9.8732(1) Å. The material is isostructural with the mineral langbeinite, having two crystallographically distinct, octahedrally coordinated Fe³⁺ ions in the asymmetric unit. Mössbauer effect spectroscopy and magnetic susceptibility measurements show that KBaFe₂(PO₄)₃ orders as an L-type ferrimagnet with 3.9 < T_C < 4.2 K. The variation of H_int has been monitored by Mössbauer spectroscopy in the temperature range 1.3 < T < 4.2 K.     

X-ray crystal analysis of tricyclohexyltin trifluoroacetate and Mössbauer data for (cyclo-C6H11)3SnO2CR′ (R′ = CH3, CH2CL,CHCL2, CCl3 and CF3)

The halogenocarboxylates (cyclo-C₆H₁₁)₃SnO₂CR′, (R′ = CH₃, CH₂Cl, CHCl₂, CCl₃ and CF₃) have been prepared, and characterized by Mössbauer and IR spectroscopy. The crystal structure of (cyclo-C₆H₁₁)₃SnO₂CCF₃ has been determined by X-ray analysis. The crystals are orthorhombic, space group Pcmn, with unit cell parameters a 14.390 ± 0.004, b, 13.427 ± 0.004, c 11.516 ± 0.003 Å. The structure was resolved by Patterson methods and refined to an R value of 0.147. The coordination about the tin atom can be considered distorted trigonal-pyramidal or distorted tetrahedral. Mössbauer data are explained in terms of distortions of bond angles about the tin atom.     

Structure de La2Fe2S5 et de La2Fe1.87S5

The compound La₂Fe₂S₅ is orthorhombic. Cell parameters are: a = 3.997(2)Å; b = 16.485(5)Å; c = 11.394(4)Å. Space group is Cmc2₁ (Z = 4. In the cell, chains of polyedra comprised of sulfur atoms tetrahedrally or octahedrally coordinating centrally located iron atoms give a monodimensional character to the structure. This one is refined to R = 0.037. To complete the study of these chains, in the La₂Fe_2?xS₅ system, vacancies are introduced on iron atom sites. The ordered compound, La₂Fe_1.87S₅, having such vacancies, is an orthorhombic superstructure of the stoechiometric compound. Cell parameters are: a = 3.9996(5)Å; b = 49.508(3)Å; c = 11.308(3)Å. Space group is Cmc2₁ and Z = 12. The structure is refined to R = 0.068. Only two iron atom sites have vacancies. One is tetrahedral, the other octahedral. In this last case the chain deformations are the more important. The chain becomes a sort of tunnel made of atoms of sulfur, with in its center the short iron-iron separation of 2.82 Å.     

Mössbauer and single crystal X-ray studies of polymeric dimethylchlorotin acetate

The solid state structure of dimethylchlorotin acetate has been investigated by Mössbauer spectroscopy and single crystal X-ray analysis. Tin-119 Mössbauer spectra have been recorded at 80 K and 300 K, and the measured isomer shift and quadrupole splitting parameters have been correlated with the crystallographic data. The crystal structure has been determined using heavy-atom methods in conjunction with least-squares refinement of data measured on a two-circle X-ray diffractometer. Crystals are orthorhombic, space group Pna2₁, with four formula weights in a cell having the dimensions a = 9.315(3), b = 11.061(3), c = 7.656(2) Å and U = 788.78 ų. The observed and calculated densities are 2.07 and 2.05 mg m^?3, respectively. The structure was refined using 842 observed reflections to give conventional discrepancy factors of R = 0.040 and R' = 0.044. The crystal structure is composed of Me₂ClSn units bridged by acetate ligands giving rise to polymeric chains which run along the a direction. The tin atom is in a distorted trigonal bipyramidal environment consisting of two axial oxygen atoms distanced 2.165(6) and 2,392(7) Å from the metal, and equatorial positions occupied by two methyl groups and a chlorine atom. Distortions within the coordination polyhedron may be attributed to a further weak but apparently significant tin-oxygen interaction (Sn-O 2.782(7) Å), resulting in the tin atom becoming six-coordinate.     

Crystal structure and magnetic properties of tris(2-hydroxymethyl-4-oxo-4H-pyran- 5-olato-κ2O5,O4)iron(III)

Tris(2-hydroxymethyl-4-oxo-4H-pyran-5-olato-κ²O⁵,O⁴)iron(III) [Fe(ka)₃], has been characterised by magnetic susceptibility measurements Mössbauer and EPR spectroscopy. The crystal structure of [Fe(ka)₃] has been determined by powder X-ray diffraction analysis. Magnetic susceptibility and EPR measurements indicated a paramagnetic high-spin iron centre. Mössbauer spectra revealed the presence of magnetic hyperfine interactions that are temperature-independent down to 4.2?K. The interionic Fe³⁺ distance of 7.31?Å suggests spin-spin relaxation as the origin of these interactions.     

Crystal structure and the magnetic properties of tris(2-chloromethyl-4-oxo-4H-pyran-5-olato-κ2O5,O4)iron(III)

The tris(2-chloromethyl-4-oxo-4H-pyran-5-olato-κ²O⁵,O⁴)iron(III), [Fe(kaCl)₃], has been synthesized and characterized by the crystal structure analysis, magnetic susceptibility measurements, Mössbauer, and EPR spectroscopic methods. The X-ray single crystal analysis of [Fe(kaCl)₃] revealed a mer isomer. The magnetic susceptibility measurements indicated the paramagnetic character in the temperature range of 2 K–298 K. The EPR and Mössbauer spectroscopy confirmed the presence of an iron center in a high-spin state. Additionally, the temperature-independent Mössbauer magnetic hyperfine interactions were observed down to 77 K. These interactions may result from spin–spin relaxation due to the interionic Fe³⁺ distances of 7.386 Å.     

First order magnetic transition,magnetic structure,and vacancy distribution in Fe2P

The para- to ferromagnetic transition in Fe₂P has been studied using Mössbauer spectroscopy. The magnetic hyperfine fields drop abruptly from about half of their saturation values to zero at 214.5 K indicating a first order transition. The isomer shifts show a discontinuous change at the transition point. For some samples the transition takes place over a wide temperature range, probably due to impurities and other imperfections in the samples. From the magnetic hyperfine fields at 15 K the magnetic moments can be deduced to be 1.14 μ_B and 1.78 μ_B for Fe(1) and Fe(2), respectively. An assignment of the components in the Mössbauer spectra to the two crystallographically nonequivalent iron positions has been made from the temperature variation of the spectra.The ordering of metal vacancies has been investigated by a Mössbauer study of a nonstoichiometric Fe₂P sample and by an X-ray diffraction study of a nonstoichiometric Mn₂P crystal.     

Synthesis and x-ray crystallographic characterization of (μ3-Bi)2Fe3(CO)9: A reformulation of Hieber's Bi2Fe5(CO)20

When [HFe(CO)₄]^? is treated first with NaBiO₃ and then dilute H₂SO₄, a complex mixture of neutral metal carbonyl clusters results, some of which can be extracted into petroleum ether. Upon prolonged standing the extract yields a precipitate which has been characterized by X-ray crystallography as Bi₂Fe₃(CO)₉.The complex Bi₂Fe₃(CO)₉ crystallizes in the centrosymmetric orthorhombic space group Cmcm (D_2h¹⁷; No. 63) with a 10.616(2) Å, b 13.458(3) Å, c 11.347(3) Å, V 1621.1(7) ų and Z = 4. Single-crystal X-ray diffraction data (Mo-K_α, 2θ = 4.5–55.0°) were collected on a Syntex P2₁ four-circle diffractometer and the structure was refined to R_F 5.4% and R_WF 4.5% for all 1039 independent data (R_F 4.5% and R_WF 4.5% for those 851 reflections with |F₀| > 3.0σ(|F₀|)). The molecule lies on a site of crystallographic C_2v symmetry and is disordered. The individual molecules have a trigonal bipyramidal Bi₂Fe₃ core with the bismuth atoms occupying the apical sites (BiFe 2.617(2)–2.643(2) Å, FeFe 2.735(5)–2.757(5) Å). Each iron atom is linked to three terminal carbonyl ligands and the molecule has approximate C_3h symmetry. The nine peripheral oxygen atoms are ordered and define a tricapped trigonal prism. The equatorial iron atoms are disordered with the two Fe₃ triangles mutually displaced by approximately 30°; the disordered ensemble has approximate D_3h symmetry.     

A Mössbauer and X-ray study of Fe2P1−xBx compounds (x < 0.15)

Boron/phosphorus substitution in Fe₂P has been studied by ⁵⁷Fe Mössbauer spectroscopy. The magnetic ordering temperature increases rapidly with increasing boron content. Replacement of a phosphorus atom by boron in the immediate environment of an iron atom results in a substantial increase of the magnetic hyperfine field, while the centroid shift and the quadrupole splitting are almost unchanged. The hyperfine parameters for iron atoms at larger distances from the boron atom remain unaffected. Boron substitutes preferentially for phosphorus at the singlefold P(2) position in the Fe₂P structure.     

Mössbauer study of the thermal decomposition products of BaFeO4

A pure sample of a hexavalent iron compound, BaFeO₄, was decomposed at temperatures below 1200°C at oxygen pressures from 0.2 to 1500 atm. In addition to the already known BaFeO_x (2.5 ≦ x < 3.0) phases with hexagonal and triclinic symmetry, two new phases were obtained as decomposition products at low temperatures. One of the new phases, with composition BaFeO_{2.61 – 2.71}, has tetragonal symmetry; lattice constants are a₀ = 8.54 Å, c₀ = 7.29 Å. The phase is antiferromagnetic with Néel temperature estimated to be 225 ± 10 K. Two internal fields observed on its Mössbauer spectra correspond to Fe³⁺ and Fe⁴⁺. In the other new phase, with composition BaFeO_2.5, all Fe³⁺ ions had the same hyperfine field; it too is antiferromagnetic with a Néel temperature of 893 ± 10 K. Mössbauer data on the hexagonal phase coincided with earlier results of Gallagher, MacChesney, and Buchanan [J. Chem. Phys.43, 516 (1965)]. In the triclinic-I BaFeO_2.50 phase, internal magnetic fields were observed at room temperature, and it was supposed that there were four kinds of Fe³⁺ sites. The phase diagram of BaFeO_x system was determined as functions of temperature and oxygen pressure.     

L'oxyde double Fe2WO6. I. Structure cristalline et filiation structurale

The authors have found a new structural type, related to α-PbO₂, called tri-α-PbO₂. The oxide Fe₂WO₆ is the prototype. It crystallizes in the orthorhombic system with the following cell parameters: a = 4.576 Å, b = 16.766 Å, and c = 4.967Å. The space group is Pbcn. The structure has been determined by X-ray single-crystal methods and refined by least-squares procedures (R = 0.065).The structure consists of zig-zag chains parallel to the c-axis. Each such chain is built up by MO₆ (M = Fe or W) octahedra-sharing edges. The chains are linked together by corner sharing. There are two types of chains: one containing only iron atoms, the other being an ordered 1-1 arrangement of iron and tungsten atoms.     

Hyperfine interactions in MgF2:Fe2+ and ZnF2:Fe2+ by Mössbauer spectroscopy

Measurement of the magnetic hyperfine interaction in paramagnetic Fe²⁺ in ZnF₂ and MgF₂ by Mössbauer spectroscopy is reported. The results, ?275 ± 3 kOe and ?270 ± 3 kOe for ZnF₂:Fe²⁺ and MgF₂:Fe²⁺ respectively are compared with a previous analysis of hyperfine interactions in the rutile fluorides.     

Synthesis and phase formation in M 0.5(1+x) 2+ FexTi2−x (PO4)3 phosphate series

New complex phosphates of titanium, iron, and alkaline-earth metals have been synthesized. X-ray powder diffraction, differential thermal analysis (DTA), and IR spectroscopy are used to study phase formation in the series of M_0.5(1+x)Fe_xTi_2?x (PO₄)₃ (M = Mg, Ca, Sr, Ba) phosphates. Individual compounds and solid solutions are found to crystallize in the NaZr₂(PO₄)₃ and K₂Mg₂(SO₄)₃ structure types. Their crystal parameters are calculated. CaFeTi(PO₄)₃ is studied using Mössbauer spectroscopy. Its structure is refined by the Rietveld method: space group $R\bar 3$ c, Z = 6, a = 8.5172(1), Å, c = 21.7739(4) Å, V = 1367.91(4) ų.     

Refinements of the six-layer structures of the R-type hexagonal ferrites BaTi2Fe4O11 and BaSn2Fe4O11

The structures of BaTi₂Fe₄O₁₁ and BaSn₂Fe₄O₁₁ have been determined from neutron powder diffraction data collected at 300 K using the Rietveld profile refinement. The compounds were found to be isostructural, space group $\text{P6}{}_3\text{mmc}$. BaTi₂Fe₄O₁₁: a = 5.8470(2) Å, c = 13.6116(9) Å, V = 403.01(5) ų, M = 632.6, Z = 2, D_calc. = 3.09 Mg m^?3, final R-factor = 3.77. BaSn₂Fe₄O₁₁: a = 5.9624(5) Å, c = 13.7468(14) Å, V = 423.23(10) ų, M = 774.2, Z = 2. D_calc. = 3.66 Mg m^?3, final R-factor = 2.41. The structure consists of h-stacked BaO₃ and O₄ layers in the ratio 1:2. The BaO₃ layers contain a mirror plane. Between the O₄ layers three octahedral sites are occupied, and between the BaO₃ and O₄ layers an octahedral site and a tetrahedral site are occupied. Because of the mirror plane in the BaO₃ plane the latter sites both share faces in the BaO₃ plane. The octahedral sites are occupied by Fe and Ti or Sn, the pair of tetrahedral sites is occupied by one Fe atom. This Fe atom may hop between these two tetrahedral sites. The structure is considered to be constructed by two R-blocks of the BaFe₁₂O₁₉ (M) structure. Unit-cell dimensions are given of a number of isostructural compounds of general formula A^IIB^IV₂C^III₃O₁₁. Mössbauer experiments on some of these compounds were focused on the tetrahedral positions that show an unusual quadrupole splitting. A brief review is given of the observed magnetic properties of some compounds with the R-structure.     

A study of the new cubic,ordered perovskites BaLaMRuO6 (M = Mg,Fe, Co,Ni, or Zn) and the related phases La2MRuO6 (M = Mg,Co, Ni,or Zn) by 99Ru Mössbauer spectroscopy and other techniques

⁵⁷Fe and ⁹⁹Ru Mössbauer spectroscopy, coupled with magnetic susceptibility measurements down to 4.2 K, have been used to study the electronic and magnetic properties of the new cubic-ordered perovskites BaLaMRuO₆ (M = Mg, Fe, Co, Ni, or Zn). The ruthenium is present in the +5 oxidation state in all the compounds except BaLaFeRuO₆ which contains iron(III) and ruthenium(IV). All the compounds exhibit long-range antiferromagnetic order, with Néel temperatures in the range 20–40 K. Mössbauer spectra for the new compound La₂CoRuO₆ and the isostructural cubic perovskites La₂MRuO₆ (M = Mg, Ni, or Zn) confirm the presence of ruthenium(IV) in these phases and indicate that they are not ordered magnetically at 4.2 K.     

Some new results and interpretation concerning the system FeYb2S4

Stoichiometric powdered FeYb₂S₄ having a cubic (special) spinel structure was prepared. The structure was based on X-ray diffraction and Mössbauer spectroscopy. The space group is Fd3m (No. 227) and the lattice constant a₀ = 10.828Å. All the iron is divalent but only ca. 80% fills the tetrahedral 8a site while ca. 20% fills the octahedral 16d site. The ytterbium is trivalent, most of it occupying the normal octahedral 16d spinel site, but ca. 16% occupies the normally empty octahedral 16c site, having been displaced by the iron.