Structure cristalline et proprietes physiques de Cu0.75 VS2

A new compound with composition Cu_0.75 VS₂ has been prepared. Its preparation, X-Ray structure, electrical and magnetic properties are reported. The structure is related to the CdI₂-type, as in the case of the previously described Cu_xTiS₂ (1); in Cu_0.75 VS₂, Cu atoms are ordered in tetrahedral sites between the CdI₂-type subunits, whereas in Cu_xTiS₂ Cu atoms are disordered in two independent sites. The vanadium atoms are shifted with respect to the titanium sites which leads a monoclinic distortion of the hexagonal cell. The relation between the CdI₂ unit cell and the true monoclinic cell of Cu_0.75 VS₂ is:

$\text{a}{}_{\mathrm{<mtext>mono</mtext>}}\text{= 2}\text{a}{}_{\mathrm{<mtext>hex</mtext>}}\text{3}\text{;}\text{b}{}_{\mathrm{<mtext>mono</mtext>}}\text{=}\text{4}\text{3}\text{a}{}^2{}_{\mathrm{<mtext>hex</mtext>}}\text{+}\text{c}{}^2{}_{\mathrm{<mtext>hex</mtext>}}\text{9}\text{;}\text{c}{}_{\mathrm{<mtext>mono</mtext>}}\text{= 2}\text{a}{}_{\mathrm{<mtext>hex</mtext>}}$

In Cu_0.75 VS₂, vanadium atoms occupy two independent sites, three vanadium atoms forming a triangular cluster (V₂—V₃ distances are 2.91 Å and V₃—V₃ are 2.92 Å) while one vanadium atom is isolated ($\text{V}{}_1\text{?}\text{V}{}_2\text{= 3.36}\text{A}\text{?}$ and $\text{V}{}_1\text{?}\text{V}{}_3\text{= 3.37}\text{A}\text{?}$. The physical properties exhibit a transition at 50°K approximately, the magnetic susceptibility being temperature-independent above and temperature dependent below the transition (Curie-Weiss behavior). Resistivity and Hall measurements confirm the metallic nature of the compound and show the existence of the low temperature transition. The observed properties could be interpreted as a result of the low temperature localisation of the 3d electron of V₁.     

Crystal structure and magnetic properties of Cu4NiSi2S7

The structure of the compound Cu₄NiSi₂S₇ has been determined. It crystallizes in a new, monoclinic distorted sphalerite superlattice with the parameters: $\text{a}\text{= 11.551}\text{A}\text{?}$, $\text{b}\text{= 5.313}\text{A}\text{?}$, $\text{c}\text{= 8.165}\text{A}\text{?}$, β = 98.72°, $\text{V}\text{= 495.2}\text{A}\text{?}{}^3$, Z = 2, space group C2. The analogous compound Cu₄NiGe₂S₇ is isotypic. At a Neél temperature T_N = 20.2 K, Cu₄NiSi₂S₇ becomes antiferromagnetic. The magnetic moment of the paramagnetic phase is 2.6μ_B.     

High pressure synthesis of Cu2GeO4 with hausmannite structure

Copper(II)metagermanate, CuGeO₃, decomposes at high pressure to rutile-type GeO₂ and Cu₂GeO₄. Very small single crystals of Cu₂GeO₄ can be obtained by direct high pressure synthesis from CuOGeO₂ mixtures. The compound has a distorted spinel structure (Hausmannite structure, space group $\text{I}\text{4}{}_1\text{amd}$) with $\text{a}\text{= 5.593}\text{A}\text{?}$, $\text{c}\text{= 9.396}\text{A}\text{?}$, Z = 4.     

Etude magnetique et par spectroscopie Mössbauer de NH4FeF4

The NH₄FeF₄ lattice is constituted by sheets of (FeF₆^3? octahedra alternating with NH₄⁺ layers and may be described therefore as a two-dimensional material. At about 200 K the x^?1 vs. T curve shows actually a flat minimum typical of two-dimensional interactions. A calculation of the exchange integral has been performed using a high temperature series expansion technique and leads to $\text{J}\text{k}\text{= ? 26}\text{K}$. A Mössbauer spectroscopy investigation of the variation of the hyperfine field vs. T gives a Néel temperature T_N = 135 K and a critical exponent β = 0, 26. This last value is close to those obtained for RbFeF₄ and CsFeF₄ which have similar crystal and magnetic structures.     

Sur la phase CsVCl3: Etude cristallographique et magnetique

The crystal structure of CsVCl₃ has been determined by means of a Patterson synthesis and refined by full-matrix least-squares to a residual R = 0.06. The space group is $\text{P}\text{6}{}_3\text{mmc}$ with $\text{a}\text{= 7.228 (3)}\text{A}\text{?}$ and $\text{c}\text{= 6.030 (3)}\text{A}\text{?}$. The structure of CsVCl₃ belongs to the CsNiCl₃ type. The magnetic properties have been interpreted on the basis of a $\text{S}\text{=}\text{3}\text{2}$ model for Heisenberg one-dimensional interactions. The strong antifer-romagnetic intrachain V-V interactions ($\text{J}\text{k}\text{= ?115}\text{K}$) seem to result from direct t_2g - t_2g coupling and from 90° correlation superexchange coupling using the 3s chlorine orbital.     

Diffraction de laue aux neutrons appliquee a la structure magnetique modulee de NaMnCrF6

We have studied the magnetic properties of NaMnCrF₆ from neutron powder and single crystal diffraction data. The crystallographic lattice is trigonal and the parameters at 4.2K are : a = 8.989(9), $\text{c}\text{= 4.997(6)}\text{A}\text{?}$. The Bragg peaks observed on the powder data collected at 4.2K are indexed with conserving the lattice parameter a but with an irrational magnetic lattice along the c-axis : the propagation vector a = |0,0,0,0182|. The periodicity of the modulated spin structure is about 275 Å. The results of the detection of commensurate-incommensurate phase transitions by using magnetic Laue data are compared to those obtained from powder data. The development of pairs of satellites having a magnetic origin and their harmonics is followed as a function of the magnetic field up to the collapse.     

Proprietes de l'ion Cu2+ dans la structure de AgCuPO4-β

AgCuPO₄-β (high temp.) crystallizes with orthorhombic symmetry, space group: Pbca, z=8 and unit-cell parameters: a=7.500(1), b=15.751(2), $\text{c}\text{=5.702(1)}\text{A}\text{?}$. Its structure has been solved and refined to R=0.046 for 664 independent reflexions. The framework is built up with PO₄ tetrahedra, AgO₅ pyramids and CuO₅ bipyramids. The Jahn-Teller effect of Cu²⁺ and magnetic properties are discussed.     

Structures cristallines de Sc3Cu4Ge4, T.R.3Cu4Sn4 (T.R. = Y,Gd, Tb,Dy, Ho,Er), isotypes de Gd3Cu4Ge4, et de la phase apparentee Tm3Cu4Sn4

Tm₃Cu₄Sn₄ has been studied by single - crystal X - ray diffraction analysis. The structure is of a new type with space group C2/m and Z = 2:a = 16.119(2), b = 4.3935(6), $\text{c}\text{= 6.896(1)}\text{A}\text{?}$, β = 115.88(2)°, D_x = 9.32 Mgm^?3, μ(MoKα) = 52 mm^?1, F(000) = 1045, R = 0.056 for 558 independant reflexions (R_w = 0.058). Tm₃Cu₄Sn₄ is a monoclinic distorded variety of the Gd₃Cu₄Ge₄ structure type. Seven other compounds were characterized: Sc₃Cu₄Ge₄ and R. E₃Cu₄Sn₄ where R.E. = Y, Gd, Tb, Dy, Ho, Er, isostructural with Gd₃Cu₄Sn₄.     

Magnetic and crystallographic properties of Fe1−x(Cu0.5In0.5)xCr2S4 spinels

Fe_1?x(Cu_0.5In_0.5)_xCr₂S₄ spinel powders with 0 ≤ x ≤ 1 were prepared. Their lattice constant (a_o) increases linearly with x from a_o = 0.9995 nm for x = 0 to 1.0065 nm for x = 1. Cu⁺, In³⁺, and Fe²⁺ ions occupy tetrahedral A sites of the spinel lattice and Cr³⁺ ions the octahedral B sites. Spinels with 0 ≤ x ≤ 0.82 are ferrimagnets with Curie temperatures decreasing from 171 K for x = 0 to 116 K for x = 0.82. Spinels with 0.82< x≤ 1 are antiferromagnets with Néel temperatures between 31 K and 36 K. The magnetic moment of Fe_0.18Cu_0.41In_0.41Cr₂S₄ spinels was determined by susceptibility measurements to be 5.85 $\text{μ}{}_{\mathrm{<mtext>B</mtext>}}\text{molecule}$, which is equal to the calculated spin-only magnetic moment.     

Structure cristalline et proprietes physiques de CuxTiS2

The preparation, crystal structure, and electrical and magnetic properties of the compound Cu_xTiS₂ (0,7 < x < 1) are reported. This compound is a member of the family of layer compounds ABX₂ (A = Cu, Ag; B = Cr, V, Ti; X = S, Se, Te) with atoms X forming a cubic closed-packed array, atoms B occupying the octahedral holes between alternate X sheets and atoms A located in the tetrahedral holes in the remaining vacant layers. A three-dimensional X-Ray structure determination was performed on a single crystal of composition Cu_0.70TiS₂ with the final discrepancy indices R = 0.037, wR = 0.043. The structure is related to CdI₂ with the unit cell derived from 3 CdI₂ cells that are translated by $\text{|}\text{1}\text{3}\text{,}\text{1}\text{3}\text{, 1|}$ and with Cu atoms disordered in two independent tetrahedral sites between the CdI₂-type subunits. The magnetic susceptibility exhibits Pauli-paramagnetic behaviour and the results of Hall measurements confirm the metallic nature of the compound.     

Existence de la structure triramsdellite : Li3FeSb2O8

An ordered ramsdellite Li₃FeSb₂O₈, called triramsdellite, was synthesized for the first time. This phase crystallizes in the orthorhombic system, with the possible space groups Pmcn and P2₁ cn and with the parameters $\text{a}\text{= 9.017(4)}\text{A}\text{?}$, $\text{b}\text{= 5.013(2)}\text{A}\text{?}$ and $\text{c}\text{= 9.841(4)}\text{A}\text{?}$. The X-ray powder diffraction study shows that a 1–2 type order appears between the cations belonging to the two sorts of octahedral sites A and B; these sites are preferentially occupied by lithium and antimony respectively according to the formulation |Li₃|_tet|Li_1.5Fe_0.5|^A_oct|FeSb₃|^B_octO₁₂. This structure, which can be described as built up from A₂B₄O₁₂ octahedral units, is compared to the LiSbO₃ and trirutile structures.     

Etude cristallographique du systeme FeSSc2S3 preparations et structures de FeSc2S4 et Fe0.85Sc2.10S4

The crystal structures of FeSc₂S₄ and Fe_0.85Sc_2.10S₄ have been determined by three dimensional X-ray diffraction. The cubic cells, space group Fd3m, have lattice constants $\text{a}\text{= 10,501}\text{A}\text{?}$ for FeSc₂S₄ and $\text{a}\text{= 10,444}\text{A}\text{?}$ for Fe_0.85Sc_2.10S₄. Iron is divalent and scandium trivalent. FeSc₂S₄ is a direct spinel structure, Fe_0.85Sc_2.10S₄ is near a spinel structure. Only 0,5 iron atom is on every 8a position; 0,175 Fe and 1,05 Sc lie on octahedral 16d and 16c site.     

Interactions magnetiques intra- et interclusters dans les pentafluorures RuF5 et OsF5

The nature of the magnetic interactions in RuF₅ and OsF₅ has been investigated using neutron diffraction and magnetic measurements under high applied fields. RuF₅ and OsF₅ are magnetically ordered at respectively T_N = 5 and 6 K. The magnetic structures have been determined. A model based on isolated tetranuclear clusters M₄F₂₀ (M = Ru or Os) has been applied to explain the magnetic behavior above the Néel temperature. The intracluster exchange interactions are antiferromagnetic. The fitting of the magnetization data leads to an exchange constant of $\text{J}\text{k}\text{= ?7.7}\text{K}$ for RuF₅, in good agreement with that calculated from the thermal variation of the magnetic susceptibility.     

Macle et structure cristalline de Mn0,75Ga2,17S4

Twins of $\text{Mn}{}_{\mathrm{<mtext>1?</mtext><mtext>x</mtext>}}\text{Ga}{}_{\mathrm{<mtext>2+</mtext><mtext>2</mtext><mtext>3</mtext><mtext>x</mtext>}}\text{S}{}_4$ were used for crystal structure determination. Twinning is explained by a reticular pseudomerihedry. Axis, plane and obliquity of the twin have been determined. Cell dimensions are: $\text{a = b}\text{= 5.456(2)}\text{A}\text{?}$; $\text{c}\text{= 10.220(4)}\text{A}\text{?}$; α = β = γ = 90°; space group 14; Z = 2. The final R value is 0.059. The material is isostructural with CdGa₂S₄.     

Polymorphisme sous pression de Sm2Ge2O7 et identification de la nouvelle phase H de la serie des digermanates de terres rares

The pressure-temperature phase diagram of Sm₂Ge₂O₇ was determined up to 80 kbar and 1400°C. In this pressure-temperature range only two phases were found. The B″ triclinic phase synthetised at atmospheric pressure is stable up to 40 kbar and at higher pressures appears the H phase which is a new type of structure in the rare earth digermanate series. The lattice parameters of the H phase were determined on small single crystals which were grown with water as mineralizer. The symmetry of the H phase is hexagonal with a space group P 6/m m m. The cell parameters of H-Sm₂Ge₂O₇ are $\text{a}\text{= 11,26}\text{A}\text{?}$ and $\text{c}\text{= 31,80}\text{A}\text{?}$. The measured density is 7,01 g/cm³ and therefore the cell contains twenty seven Sm₂Ge₂O₇ units. The calculated density is 7,16 g/cm³. The X-ray diffraction pattern of H-Gd₂Ge₂O₇ previously obtained can be indexed with similar parameters $\text{a}\text{= 11,19}\text{A}\text{?}$ and $\text{c}\text{= 31,65}\text{A}\text{?}$.     

Une structure derivee de celle du spinelle la structure de Fe0.76 Yb2.16 S4

Single crystals of so-called “FeYb₂S₄ spinel” were prepared and their crystal structure was solved. The cubic cell, space group Fd3m, has a lattice constant $\text{a}\text{= 10.69}\text{A}\text{?}$. From X-rays determinations, its content is (Fe_0.76 Yb_2.16 S₄) × 8. Iron is divalent and ytterbium is trivalent. Ytterbium is in two series of octahedral sites, which are partially filled : 0.96 Yb and 0.04 ? on every 16d position, 0.12 Yb and 0.88 ? on every 16c position. Only 0.76 iron atom is in every 8a position of the spinel.     

Metal-ion distribution and magnetic structure of Fe-substituted cobaltite spinel: FeCo2O4

The metal ion distribution of FeCo₂O₄ (cubic spinel) which was quenched from 900°C in air was determined to be ($\text{Fe}$³⁺_0.18$\text{Co}$²⁺_0.82) [$\text{Fe}$³⁺_0.82$\text{Co}$²⁺_0.18 Co^III+_1.0] O₄ with the neutron diffraction method. The oxygen spacial parameter u was determined to be 0.382 ± 0.002. The magnetic structure was explained as a Néel type ferrimagnet and the origin of the spontaneous magnetization was attributed to the uncompensation of the spins between A- and B-site of the spinel lattice. The magnetic moment per molecule was estimated to be 0.70 μB.     

Preparation of a new Cu-substituted cobaltite spinel : CuCo2O4

CuCo₂O₄ spinel with tetragonal distortion was synthesized under high temperature-pressure conditions. Its calculated lattice constants were a = 8.154 and $\text{c}\text{= 7.875}\text{A}\text{?}$ ($\text{c}\text{a}\text{= 0.966}$ at room temperature). An antiferromagnetic ordering occurred at 24K and the effctive Bohr magneton of 1.74 showed that the copper ion was divalent state. From crystallographic and magnetic measurements, the copper cobaltite was expressed as (Cu²⁺) [Co₂^III]O₄.     

Crystal structure of cubic MnSc2S4 and Mn2.29Sc1.14S4

The crystal structure of MnSc₂S₄ ($\text{a}\text{= 10.613}\text{A}\text{?}$, space group Fd3m) and Mn_2.29Sc_1.14S₄ ($\text{a}\text{= 10.523}\text{A}\text{?}$, space groupe Fd3m) were determined by three dimensional X-Ray diffraction. MnSc₂S₄ is a normal spinel structure and the atomic distribution shows that Mn_2.29Sc_1.14S₄ structure is intermediate between the rocksalt (MnS) and the spinel (MnSc₂S₄) types. Similar behaviour of Mn and Fe atoms in MnSSc₂S₃ and FeSSc₂S₃ systems was observed.     

La structure cristalline de Ca4Fe9O17: Des feuillets “hexagonaux” d'octaedres FeO6 et de bipyramides FeO5 lies par des tetraedres FeO4

The new calcium ferrite Ca₄Fe₉O₁₇, belonging to the CaFe_2+nO_4+n family ($\text{n}\text{=}\text{1}\text{4}$), has not the same stacking process of “FeO” blocks in “CaFeO₄” blocks, as the others terms of the series.It crystallizes in the monoclinic system, space group C2 with the parameters: $\text{a}\text{= 10,441}\text{A}\text{?}$, $\text{b}\text{= 6,025}\text{A}\text{?}$, $\text{c}\text{= 11,384}\text{a}\text{?}$ and β = 98°80. Its structure is characterized by the presence of iron atoms in oxygen octahedra and trigonal based bipyramides stacking in hexagonal layers along $\text{c}$.These layers are linked by iron atoms on tetrahedral sites. Calcium atoms are hexagonaly located around each tetrahedron.