Etude par microscopie electronique de l'oxydation de l'hydrate ReO2, 2H2O

Oxidation of hydrate ReO₂, 2H₂O is studied by electron microscopy and X-ray powder diffraction. It yields to ReO₃. Evidence is given of existence of a structure Me₂O₅ as intermediary compound. The microstructure of single crystals prepared by sublimation under reduced pressure of oxygen, shows planar defects in agreement with the transformation Re₂O₅ → ReO₃.     

Contribution a l'etude de la conductivite ionique de l'orthophosphate Na3PO4

The present work is concerned with the ionic conductivity of pure trisodium orthophosphate Na₃PO₄, devoid of any trace of hydroxide NaOH. At the allotropic transition (330°C), we observe a jump of the ionic conductivity and a slight decrease in the activation energy (ΔE = 0,70 ± 0,02 eV for the quadratic variety and ΔE = 0,60 ± 0,04 eV for cubic γ-Na₃PO₄). Na₃PO₄ can be considered to be an electrolytic solid with medium conductivity ($\text{σ = 1.10}{}^{\mathrm{?4}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$ at 370°C).     

Influence de l'addition de cuivre sur les proprietes structurales et physiques de VO2

Magnetic susceptibility, DTA, X-ray diffraction and EPR of Cu_xV_1?xO₂ samples have been studied. A new Q-phase stable at low temperature is reported. Analogies with M^III_xV_1?xO₂ phases (M^III = Al, Cr, Fe) are discussed.     

Contribution a l'etude du polymorphisme de Ga2S3: Structure cristalline de Mn0,23Ga1,85S3

The Mn_0.23Ga_1.85S₃ phase belongs to the solid solution $\text{ф}{}_0$, stable at low temperature in the Ga₂S₃MnS system. It is hexagonal superstructure of the wurtzite, with the Ga₂S₃α′ type ($\text{a}\text{= 6.397}\text{A}\text{?}$; $\text{c}\text{= 18.027}\text{A}\text{?}$Z = 6; space groupe P6₁ or P6₅). Its crystal structure has been refined by the least squares method to a final R = 0.06 with 323 independant reflections. This structure is closely related to Ga₂S₃ α described by Hahn and Frank, and differs only by the partial occupation of the vacant metal site of Ga₂S₃ by Mn atoms in statistical disorder.     

Distribution du fluor et de l'oxygene dans l'oxyfluorotantalate de potassium K2Ta4O9F4

The crystal structure of potassium tantalum oxide fluoride K₂Ta₄O₉F₄ has been previously determined by X ray-diffraction, but this technique is unable to distinguish in the lattice between oxygen and fluorine atoms. From NMR measurements on ¹⁹F it is possible by a Van Vleck second moment approach to locate the F^? ions at the corners of the octahedra, forming infinite Ta-F-Ta … chains along the $\text{c}$ axis.     

Structure cristalline d'une nouvelle variete de pyrophosphate de nickel: Ni2P2O7

Three forms of nickel pyrophosphate are already known. A new form was prepared and structure determined by Patterson method. σ Ni₂P₂O₇ is monoclinic with a = 5.212(3), b = 9.913(5), $\text{c}\text{= 4.475(3)}\text{A}\text{?}$, β = 97°46(10). The space group is $\text{P}\text{2}{}_1\text{a}$. The structure was refined until a R value of 0.041 for 1374 independent reflexions. Framework is built with P₂O₇ groups and NiO₆ octaedra. The P-O-P bonding is linear. σ Ni₂P₂O₇ is isotypic with the pyrosilicate Er₂Si₂O₇.     

Crystal Structure of (H3O)2[(UO2)2(SeO4)3(H2O)2](H2O)3.5

Crystals of (H₃O)₂[(UO₂)₂(SeO₄)₃(H₂O)₂](H₂O)_3.5 were prepared from aqueous solutions by evaporation. The crystal structure [monoclinic system, space group P2₁/m, a = 11.9402(11), b = 13.6452(14), c = 13.7271(12) Å, β = 109.436(7)°, V = 2109.1(3) ų] was solved by the direct method and refined to R ₁ = 0. 048 (wR ₂ = 0. 082) for 3677 reflections with |F _hkl |F _hkl |. The structure consists of [(UO₂)₂(SeO₄)₃(H₂O)₂]₂₋ layers arranged parallel to the (010) plane. The layers are formed by uranium and selenium coordination polyhedra sharing common vertices and are linked with each other by hydrogen bonds through the H₂O and H₃O⁺ groups arranged between the layers. __________ Translated from Radiokhimiya, Vol. 47, No. 5, 2005, pp. 412–414. Original Russian Text Copyright ? 2005 by Krivovichev, Kahlenberg.     

Structure cristalline de Mn0, 4Er4, 6S7

The crystal structure of Mn₀, ₄Er₄, ₆S₇ ($\text{a}\text{= 12,573 (4)}\text{A}\text{?}$, $\text{b}\text{= 11,390 (4)}\text{A}\text{?}$, $\text{c}\text{= 3,777 (4)}\text{A}\text{?}$, γ = 105,45°, space group B2/m, Z = 2) has been refined by a least square method to a final R = 0,045, with 1431 independant reflections. The octahedral positions are occupied either by Er and Mn atoms or by Er atoms only and the prismatic sites by Er atoms.     

Structure cristalline d'un phspho-tellurate de rubidium : Te(OH)6.Rb2HPO4.RbH2PO4

Te(OH)₆.Rb₂HPO₄.RbH₂PO₄ is monoclinic with_°: a = 12.26(1) b = 7.059(3) c = 8.225(3) A β = 90.32(5)° and Z = 2. The space group is $\text{P}\text{2}{}_1\text{a}$. Crystal structure has been solved by using 1093 independant reflexions with a final R value 0.051. As already observed in the first crystal structures of phospho-tellurates the main feature of this atomic arrangement is the coexistence of two different types of anions in the unit cell (PO₄ and Te(OH)₆ groups).     

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 of (H3O)6[(UO2)5(SeO4)8(H2O)5](H2O)5

Crystals of (H₃O)₆[(UO₂)₅(SeO₄)₈(H₂O)₅](H₂O)₅ were prepared from aqueous solutions by evaporation. The crystal structure [monoclinic system, space group P2₁/m, a = 13.835(2), b = 13.4374(16), c = 14.310(3) Å, β = 108.004(14)°, V = 2530.1(7) Å ³] was solved by the direct method and refined to R ₁ = 0.090 for 4409 reflections with |F _hkl ≥ 4σ|F _hkl |. The structure is based on [(UO₂)₅(SeO₄)₈(H₂O)₅]⁶⁻ layers arranged parallel to the (101) plane; these layers have a unique topological structure. The U(1)O₆(H₂O) and U(3)O₆(H₂O) linked through selenate groups form chains running along [ [`1]\bar 1 01] direction. The chains are combined in layers by U(2)O₆(H₂O) bipyramids. The layers are linked with each other by hydrogen bonds through the H₂O and H₃O⁺ groups located between the layers.     

Structure cristalline du spinelle CdEr2S4

The crystal structure of CdEr₂S₄ is solved from single crystal determinations. The R factor is 0.06 for 120 independent reflections. It is normal spinel, with regular occupancy of the sites. Interatomic distances are : 2.67 Å for ErS, and 2.57 Å for CdS.     

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.     

Structure cristalline du seleniure d'Etain IV et de thallium I : Tl2SnSe3

The cell is orthorhombic, a = 8.051(3); b = 8.169(3); $\text{c}\text{= 21,24(1)}\text{A}\text{?}$; Z = 8; space groupe Pnam, d_calc = 7.2; d_obs = 7.1; μ = 897 cm^?1. R = 0.065 for 1636 reflections.The anion Sn₂Se^4?₃ is formed by two SnSe₄ tetrahedra, which have a common edge. Two kinds of thallium atoms are observed, with different coordinations.     

Structure cristalline et proprietes physiques de Cu0.65VS2

A second form of compounds Cu_xVS₂ is described here. As in Cu_0.75VS₂ (1) the structure of Cu_0.65VS₂ is related to the CdI₂-type. In Cu_0.75VS₂, Cu atoms are ordered in tetrahedral sites between the CdI₂-type subunits, whereas in the Cu_0.65VS₂, Cu atoms are partially disordered and occupy 4 different sites. Both structures differ from one another in vanadium atoms arrangements: In Cu_0.75VS₂, V-atoms form triangular clusters while in Cu_0.65VS₂ they form zigzag chains perpendicular to the hexagonal axis. The physical properties show a metallic type behaviour. Resistivity decreases with temperature with low 300 K/4.2 K ratio according to a disordered nature of the compound. Magnetic susceptibility shows a Pauli paramagnetism with an additionnal Curie-Weiss term due to a relatively large amount of paramagnetic impureties (0,9 % V³⁺ atoms). The observed low temperature localisation of the 3d electrons in Cu_0.75VS₂ disappears in the case of Cu_0.65VS₂.     

Phenomene de croissance en spirale de l'oxyde ReO2 monoclinique

During the study of polymorphic transformation from monoclinic to orthorhombic ReO₂, particular crystal growth of monoclinic oxide has been observed. Electronic microscopy results lead up to conclude that this phenomenon is spiral growth. Original electron diffraction patterns are obtained which show two kinds of polygonal spirals.     

Proprietes magnetiques de l'oxyde Eu2O3 monocristallin

Single crystals of europium oxide Eu₂O₃ with monoclinic B structure were prepared by the Verneuil process. The magnetic properties of these crystals have been studied. Paramagnetic susceptibility measurements have been performed for various orientations of the crystal with respect to the magnetic field at constant temperatures (5,77 and 300 K) as well as at increasing temperatures (5 – 1000 K). They show an anisotropy. An interpretation of this phenomenon is proposed.     

Structure cristalline du monophosphate AgCoPO4

AgCoPO₄ is a new type of ABPO₄ framework with a twofold oxygen coordination for silver atoms and a five fold coordination for cobalt atoms. Crystal structure has been solved using both Patterson and direct methods with a final R value of 0.038 for 2097 independent reflexions. The symmetry is triclinic P$\text{1}$ with a unit cell: a = 9.516(2), b = 5.574(1), c = 6.572(2) A, α = 102°20(10), β = 106°16(10), γ = 80°08(10) and Z = 4.     

Presence de l'eau dans V2O5 non cristallin

Non cristalline pentoxide V₂O₅ obtained from molten V₂O₅ using quenching method contains a few amount of water. Thermogravimetry, thermal analysis, mass spectrometer, aqueous dissolution demonstrate that it exists a relation between non cristalline structure and water bond. At 190°C, the oxide crystallises at the same time that the water is eliminated.