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.     

De nouveaux stannures ternaires de rhodium et d'elements des terres rares : TR2Rh3Sn5 OU TR = Y,Gd, Tb,Dy, Ho. structure cristalline et proprietes electriques et magnetiques de Y2Rh3Sn5

New ternary stannides are reported : RE₂Rh₃Sn₅ (RE = Y, Gd, Tb, Dy, Ho). Y₂Rh₃Sn₅ has been studied by single - crystal X-ray diffraction analysis. Its structure is of a new type with space group Cmc2₁ and Z = 4 : a = 4,387(2), b = 26,212(4), $\text{c}\text{= 7,1550(8)}\text{A}\text{?}$, D_x = 8,71 Mgm^?3, μ(AgK_α) = 17 mm^?1, F(000) = 1851, R = 0,045 for 478 independant reflexions (R_w = 0,046). This structure is characterized by a tridimensionnal lattice of RhSn covalent bonds with two very different sites for yttrium. Y₂Rh₃Sn₅ is diamagnetic and semimetallic according to its electrical properties.     

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.     

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.     

Etude magnetique des phases du systeme Fe2O3TeO2 structure magnetique de Fe2TeO5 à 4,2°K

The magnetic study of the three compounds isolated in the Fe₂O₃ - TeO₂ system are described. Among them, Fe₂TeO₅ is antiferromagnetic with T_N ? 360°K. The magnetic structure is discussed and corresponds with the P2'₁/c Shubnikov group.     

Croissance cristalline des deux formes de LiIO3

The existence conditions of hexagonal and tetragonal LiIO₃ in aqueous solution are investigated from experimental solubility and supersolubility curves. This study establishes the growth conditions for both structures. X ray diffraction measurements show that an irreversible transformation from hexagonal into tetragonal structure occurs at the temperature T_c = 255 ± 1° C.     

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.     

Etude au microscope electronique des phenomenes de transition de phases dans des monocristaux d'oxyde V2O3 pur et dope au chrome

An investigation by electron microscopy confirms the low temperature transition in single crystal of V₂O₃ and V_2?xCr_xO₃ (x = 0,048). The twin planes were identified in the corundun structure as (1 1 2 0)_M. An explanation is proposed.     

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.     

Un nouveau sulfure de molybdene : Mo3S4 preparation,proprietes et structure cristalline

Un nouveau sulfure de molybdène : Mo₃S₄, isostructural de Mo₃Se₄, a été préparé. Sa maille cristallographique est rhomboédrique : a = 6, re A ; α = 91°34 ; Z = 2 ; groupe spatial R3?. Sa structure est caractérisée par un motif Mo₆S₈ constitué d'un cluster octaédrique Mo₆ ($\text{Mo}\text{}\text{Mo}\text{= 2, 69}\text{A}\text{?}$ et 2, 86 Å) inscrit dans un cube déformé de soufre.     

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.     

Preparation,cristallogenese et caracterisation des bromures mixtes de lanthanide,de sodium et de cesium Cs2 NaLn (III) Br6

Single crystals of the new perovskites Cs₂Na Ln (III) Br₆ (with Ln (III) = Ce, Nd, Gd, Y) have been grown by the Bridgmann-Stockbarger method, using sealed silica-glass ampoules. They have been characterised by analytical and standard X-Ray methods; they crystallised with cubicface centered lattices, the parameters of which are: $\text{a}\text{= 11.508 - 11.421 - 11.370 - 11.304}\text{A}\text{?}$ for Ln = Ce - Nd - Gd - Y.     

Affinement de la structure cristalline de Eu3S4

The crystal structure of Eu₃S₄, type Th₃P₄, was refined, on single crystal data, to a R value of 0.026. Only one site may be attributed to europium, accordingly the Eu²⁺ and Eu³⁺ ions are not differentiated.     

Étude expérimentale de la transmission d'électrons d'énergie inférieure à 3 keV à travers des cibles minces d'argent et de cuivre

We have carried out an experimental study of the transmission of electrons with energy below 3 keV through silver and copper self-supporting targets. The measurements were performed with a hemispherical retarding field system and results concerning the transmission coefficient and the energy distribution were obtained. The particular geometry of the collector allowed angular distributions to be obtained and some first results on the energetic angular distributions are given.     

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.     

Etude in situ par spectrométrie vibrationnelle de couches minces electrochromes d'oxyde de tungstène WO3 et d'oxyde de molybdene MoO3

Raman spectroscopy, internal and specular I.R. reflection spectroscopies have been applied to WO₃ and MoO₃ thin films (～ 5,000 A). These films are amorphous and transform to crystalline materials at 400°C. Structural similarities between WO₃ films and the new hexagonal form of WO₃ may explain the electrochromic properties of the former.     

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.     

Polymorphisme de l'hexahydroaluminate trisodique Na3AlH6

Structural investigations on the cryolite-like compound Na₃AlH₆ have been carried out using high-temperature diffractometry. α-Na₃AlH₆ which crystallises in a monoclinic pseudo-cubic system under room-temperature conditions exhibits at 525 K a polymorphic transition into a f.c.c. form β-Na₃AlH₆. This result has been established by high-pressure-high-temperature studies. From structural point of view Na₃AlH₆-β is to be related to the high temperature modification of cryolite Na₃AlF₆