Structure cristalline d'une phase cubique desordonnee de type ReO3 excedentaire en anions : ZrF2,67O0,67

The crystal structure of cubic disordered anion-excess ReO₃-related ZrF_2.67O_0.67 (space group Pm3m, $\text{a}\text{= 3.997(2)}\text{A}\text{?}$) has been determined by single crystal X-ray diffraction techniques and refined to a R = 0.038-value. Two different kinds of anions are found, one X(1) slightly displaced (by 0.27 Å) from the ideal ReO₃-anionic site, the other X(2) more considerably (by 1.16 Å). As previously proposed (8,14) the anion-excess over the parent ReO₃-type structure, is accomodated by the formation of interstitial X(2)-X(2) pairs across a vacant X(1) site.The most likely anionic arrangements around zirconium atoms are assessed and on those basis, the structure is described as a disordered three-dimensional framework of edge sharing ZrX(1)₅X(2)₂ pentagonal bipyramids and corner sharing ZrX(1)₅X(2) distorted octahedra.     

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.     

Synthese d'une nouvelle famille d'antimoniates de structure grenat

The existence of complex antimonates with the garnet structure is discussed, and a number of such compounds have been effectively synthesized and investigated by X-ray diffractometry and vibrational spectroscopy. The infrared spectra confirm the predicted octahedral coordination of Sb⁵⁺ cations.     

Obtention par trempe a partir de l'etat liquide d'une nouvelle phase dans le systeme Nd2O3.Al2O3. etude comparative avec Nd4Ga2O9

By using splat cooling devices associated with laboratory solar furnace a new phase is obtained in the neodymium rich part of the Al₂O₃Nd₂O₃ system. X ray and optical absorption studies and comparisons with Nd₄Ga₂O₉ show that the two phases are isostructural and monoclinic (space group P_21/C) with Al³⁺ in tetrahedral coordination. Optical examinations show that substitution of Al³⁺ by Si⁴⁺ induced a disorder on the neodymium site.     

Synthesis and characterization of nanocrystalline manganese pyrophosphate Mn2P2O7

Mn₂P₂O₇ polyhedral particles were synthesized by simple and cost-effective method using manganese nitrate hydrate and phosphoric acid in the presence of nitric acid with further calcinations at the temperature of 800 °C. The crystallite size obtained from X-ray line broadening is 31 ± 13 nm for the Mn₂P₂O₇. The X-ray diffraction and SEM results indicated that the synthesized nanoparticles have only the structure without the presence of any other phase impurities. The FT-IR and FT-Raman spectra show characteristic bands of the P₂O₇⁴⁻ anion. The UV–Vis–NIR spectrum confirms the octahedral coordination of Mn²⁺ ion.     

Sur une variete haute pression de PdF2 de type fluorine

A fluorite-type form of PdF₂ has been obtained from the rutile-type variety at 25°C under 50 kb and quenched to room conditions. It is the first d-element fluoride presenting this structure so far isolated under normal conditions. The transition corresponds to a volume decrease $\text{δ}\text{V}\text{V}{}_{\mathrm{rutile}}$ of 11 %. The cell parameter $\text{a}\text{= 5.322 ± 0.002}\text{A}\text{?}$ supposes a PdF distance of 2.16 Å. The thermal variation of the magnetic susceptibility suggests an antiferromagnetic behavior with an ordering temperature close to 200 K. The rutile → fluorite transition has been followed by resistivity vs. pressure measurements. Fluorite-type PdF₂ presents at room conditions a resistivity of 10⁵Ω.cm, 10⁵ lower than the rutile form.     

Etude cristallochimique d'une nouvelle serie d'oxydes doubles de rhenium et de terres rares

The preparation of a new series of heptavalent rhenium compounds of Ln₃ReO₈ type (Ln = rare earths) is described. The crystals are orthorombic for Ln = La (space groups Ccmm, Ccm2₁ or Cc2m) and Ln = Pr, …, Gd (space group B22₁2), face centered cubic of fluorite type for Ln = Tb, …, Lu and Y.     

Structure cristalline et proprietes magnetiques de la variete basse temperature TlFeBr3β

DTA and X-Ray studies of TlFeBr₃ show a transition at 384°C. The low temperature phase β-TlFeBr₃ is related to NH₄CdCl₃ and crystallizes in the orthorhombic system with $\text{a}\text{= 9.279(4)}\text{A}\text{?}$, $\text{b}\text{= 3.984(3)}\text{A}\text{?}$, $\text{c}\text{= 15.070(7)}\text{A}\text{?}$, Z = 4. The crystal structure has been determined from 564 independent reflexions. The structure contains FeBr₆ octahedra in which each Fe atom is coordinated to six Br atoms. The FeBr₆ octahedra share vertices to form infinite double chains along the b? axis. This compound behaves paramagnetically above 40 K, with a Curie-Weiss temperature of θ = 12 K and a magnetic moment of μ = 5.59 μB, but becomes antiferromagnetic below 14 K.     

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).     

Intercalation d'ions metallicinium dans les gels de V2O5

Cobalticinium and ferricinium cations have been intercalated at room temperature into the lamellar structure of V₂O₅ gels. In both cases an almost constant basal d-spacing is observed, about 13.2 Å whatever the counterion used. The basic V₂O₅ ribbon structure is not modified upon intercalation, but noticeable improvement of the order along the ribbon packing direction is obtained, especially with Co(C₅H₅)⁺₂. The 4.4 Å increase in the basal d-spacing and its high temperature evolution allow to deduce that cyclopentadienyl rings interpenetrate the V₂O₅ ribbons presumably in the usual perpendicular position. Water is involved in the intercalation mechanism which is likely of the exchange type rather than of the redox type. Intercalate formula is approximately V₂O₅, 0.4 Fe(C₅H₅)₂, x H₂O (with x < 0.5). The materials, especially the Co(C₅H₅)⁺₂ intercalate, are still stable beyond 200°C. Such a high thermal stability is quite remarkable.     

Intercalation d'ions alkylammonium et d'alkylamines a longues chaines dans les gels de V2O5

C_nH_2n+1N⁺(CH₃)₃ ions and C_nH_2n+1NH₂ amines with n ranging from 1 to 18 have been intercalated into the lamellar structure of V₂O₅ gels. Alkyl chain orientation in the interfoliar space has been deduced from the basal d-spacing evolution with the chain length : the chains are parallel, then tilted and finally perpendicular to the host lamellae as the chain length increases. Their monolayer disposition is also demonstrated. The large adaptability of the host structure proceeding from its gel state, leads to fast reaction at room temperature, especially with small polar heads such as -NH₂ (less than an hour). Contrary to usual intercalates, due to the gel state, only a mean composition can be defined. It has been found to correspond to 0.3–0.4 intercalated species per V₂O₅ : this is in good agreement with the upper limit (0.5) deduced from sterical considerations based upon a full filling of the interfoliar space. Thermal decomposition of alkyl chains restricts the stability of these intercalates to 160°C. More likely of the cationic exchange type with trimethylammonium ions, intercalation mechanism appears more complex with amines, involving probably also a host-guest charge transfer.     

Les disilicates de terres rares Ln2Si2O7: Precisions sur leur nouvelle forme cristalline X et leur polymorphisme sous pression

The new X form of rare earth disilicates Ln₂Si₂O₇ (Ln=Lu, Yb, Tm) is described by means of X-ray powder data. The X-ray indexation is made using single microcristal electronic diffraction. The investigation of structural relation between Ln₂Si₂O₇ and M₂A₂O₇ compounds as also the X-ray powder data of X-Ln₂Si₂O₇ show that this X form is isostructural with tetragonal Er₂Ge₂O₇. The rare earth coordination polyhedra and the (Si₂O₇)^6? configuration are compared with those actually known in neighbouring phases and discussed in terms of pressure effect.     

Structure cristalline de l'orthophosphate monoacide de cuivre monohydrate CuHPO4,H2O

Monophosphate hydrogen copper monohydrate : CuHPO₄,H₂O is monoclinic, space group $\text{P}\text{2}{}_1\text{a}$. The unit cell parameters are : a = 8.63(6), b = 6.35(3), $\text{c}\text{= 6.82(5)}\text{A}\text{?}$, β = 94.14(6°) and Z = 4. The crystal structure has been determined with 1249 independent reflexions and refined to a final R value of 2.9%. The crystal is built up of PO₄ tetrahedron and CuO₆ octahedron deformed by Jahn-Teller effect which are linked to form a three dimensional network.Based on the inter-ionic distances between Cu^II and O^2? in the recently determined structures of monoarsenates or phosphates, we give a value for the effective ionic radius of copper II.     

Determination structurale et proprietes de conduction d'un nouveau compose de type hollandite: K1,8(Li2,45Sb5,55)O16; mise en evidence d'une surstructure d'ordre 3

The crystal structure of a synthetic hollandite phase K_1,8(Li_2,45Sb_5,55)O₁₆ has been refined by the full matrix least-squares method using 940 three-dimensional reflexions to a final R value of 0.046. The K atoms are randomly distributed on the special positions 2b (0 0 $\text{1}\text{2}$) and 4e (0 0 ±z) with z = 0.340(4).A long-exposure rotation photograph along the c axis shows diffuse X-ray scattering between the layer line. After a thermal treatment the X-ray diffraction pattern shows weak but sharp reflexions that could be indexed by tripling the short axis. The structural studies indicate an ordering of the large K atoms within the channels.The ionic conductivity of this phase has been investigated on a single crystal by hyperfrequences method. The potassium ion conductivity is the ordre of magnitude of 10^?3 (ohm cm^?1) at 30°C along the c axis.     

Etude de nouveaux pnictures ternaires de metaux de transition isostructuraux des phases G,Ni16Mn6P7, Ni16Mn6As7

The structural properties of the new ternary phosphide and arsenide of nickel and manganese Ni₁₆Mn₆P₇ and Ni₁₆Mn₆As₇ have been investigated. This crystal structure as determined by powder X-ray diffraction was found to be the well known structure of the G phases of germanides and silicides.     

Susceptibilite paramagnetique anisotrope de monocristaux d'oxyds Nd2O3 et LaxNd2−xO3

Single crystals of neodymium oxide Nd₂O₃ and of a solid solution La_{0, 4}Nd_{1, 6}O₃ both with hexagonal A structure were obtained by Verneuil process adapted to plasma torch. Paramagnetic susceptibilities measurements were performed on these crystals at constant temperatures (5, 77 and 300 K) with various orientations of the magnetic field with regard to crystallographic axes. The curves are of the type X = A + B cos 2 θ. Variations of susceptibility versus temperature in the range 5–300 K clearly show an anisotropy. The perpendicular susceptibility varies roughly according to a Curie-Weiss law, whereas the variation of parallel susceptibility may be explained by an evolution of Nd³⁺ magnetic moment due to crystal field at low temperatures.     

Preparation chimioue et structure cristalline des tellurites de sodium et d'argent: Na2TeO3, Ag2TeO3

Sodium and silver tellurites are isotypic. The space group is $\text{P}\text{2}{}_1\text{a}$. For Ag₂TeO₃, the parameters of the monoclinic unit cell are: a = 7.000(2), b = 10.509(5), $\text{c}\text{= 4.911(2)}\text{A}\text{?}$, β = 91°51(5). The structures of sodium and silver tellurites has been determined. For Ag₂TeO₃, a R value of 0.047 is reached with 829 reflexions and for Na₂TeO₃ R = 0.024 with 1125 reflexions. The framework is built with MeO₆ edge sharing octahedra, Me = Ag,Te. Ag₂TeO₃ is a distortion of NaCl Structure.     

Proprietes magnetiques de l'oxyde de vanadium V3O7

Magnetic susceptibility and magnetization measurements on V₃O₇ from 4,2 to 600 K characterize a paramagnetic behaviour above 18 K : the samples follow a Curie-Weiss law with a Curie constant in good agreement with a spin only value $\text{S}\text{=}\text{1}\text{2}$ per V⁴⁺. At lower temperature the magnetic ordering may be attributed to a metamagnetic behaviour resulting from the layer type structure.     

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.