Synthesis,structural and physical properties of the binary molybdenum chalcogenide phase Mo15Se19 and of the related compounds M2Mo15Se19 and M3Mo15Se19 (M=group 1A metal; Sn,Pb;Cd)

We present the synthesis, structure and physical properties of the binary phase Mo₁₅Se₁₉. This material was synthesized at low temperatures by oxidation of In₂Mo₁₅Se₁₉ or In₃Mo₁₅Se₁₉ by HCl gas. X-ray studies show that Mo₁₅Se₁₉ can exist in two crystallographic forms depending upon the indium phase used as starting material. Both phases contain large open channels and crystallize in a hexagonal unit cell with lattice parameters $\text{a}{}_{\mathrm{h}}\text{= 9.46}\text{A}\text{?}$ and $\text{c}{}_{\mathrm{h}}\text{= 19.61}\text{A}\text{?}$ when prepared from In₃Mo₁₅Se₁₉ (space group P6₃/m) and $\text{a}{}_{\mathrm{h}}\text{= 9.48}\text{A}\text{?}$ and $\text{c}{}_{\mathrm{h}}\text{= 58.76}\text{A}\text{?}$ when prepared from In₂Mo₁₅Se₁₉ (space group R3?c). The two structural forms of Mo₁₅Se₁₉ were found to be superconducting at 4.3K. The ease with which indium can be removed from the ternary compounds without disturbing the binary Mo-chalcogenide networks suggested that other metallic elements could be substituted for indium. In fact, several new M₂Mo₁₅Se₁₉ and M₃Mo₁₅Se₁₉ phases were synthesized, where M = group 1A element; Sn, Pb, and Cd. Several of their physical properties are also reported.     

Oligoselenidogermanate (III): Zur kenntnis von Na6Ge2Se6 und Na8Ge4Se10

The following new oligomeric selenidogermanates (III) have been prepared and structurally characterized: Na₆Ge₂Se₆: monoclinic, space group $\text{P}\text{2}{}_1\text{c}$ (No. 14) a = 836.7(5) pm, b = 1192.4(8) pm, c = 815.8(5) pmβ = 118.63(15)°.The compound is isotypic to K₆Sn₂Te₆, essential structure elements are [Ge₂Se₆]^6? anions.Na₈Ge₄Se₁₀: triclinic, space group P1? (No. 2) a = 707.4(5) pm, b = 809.8(5) pm, c = 1065.7(6) pmα = 73.44(15)°, β = 70.84(15)°, ?= 81.73(15)°Two Ge₂Se₆ octahedra are connected by a common edge forming a six-membered cyclic [(GeSe₂)₄Se₂]^8? anion.     

Structure determination of (3D) P2NbS8

Tridimensional P₂NbS₈ crystallizes in P4?n2 tetragonal space group, with $\text{a}\text{= 12.0483(4)}\text{A}\text{?}$, $\text{c}\text{= 7.2070(5)}\text{A}\text{?}$, $\text{V}\text{= 1046.2(1)}\text{A}\text{?}{}^3$ and Z = 4. The structure was anisotropically refined down to R = 2.3% from 468 reflexions and 53 variables. It is built from [Nb₂S₁₂] biprismatic bicapped units (average $\text{d}{}_{\mathrm{Nb?S}}\text{= 2.571}\text{A}\text{?}$) made of S^?II and S^?II₂ anions (dianionic distance of 2.014(3) Å). The niobium atoms are found as isolated Nb^IV ? Nb^IV pairs ($\text{d}{}_{\mathrm{Nb?Nb}}\text{= 2.859(1)}\text{A}\text{?}$) in these niobium group otherwise linked to each other through (PS₄) tetrahedral units (average $\text{d}{}_{\mathrm{P?S}}\text{= 2.051}\text{A}\text{?}$) themselves constituting interbonded [P₄S₁₂] rings. The P₂NbS₈ three-dimensional network thus obtained is compared to the (2D) P₂NbS₈, layered phase already described.     

Rutiles of the system Tio2-FeNb2O6-NbO2 : Structural,magnetic and electron transport properties

A wide domain of rutile solid solution has been isolated in the system TiO₂-FeNb₂O₆-NbO₂. The cristallographic parameters, characteristic of the classical rutile cell, have been determined by X-ray diffraction. The Mössbauer and magnetic susceptibility study shows that in the whole domain iron exhibits the divalent state. A second type of site for Fe(II) has been observed on the limit $\text{Ti}{}_{\mathrm{1?x}}{}^{\mathrm{IV}}\text{Fe}{}^{\mathrm{II}}{}_{\mathrm{<mtext>x</mtext><mtext>3</mtext>}}$Nb^V, which has been interpreted by a small loss of oxygen involving the formation of trivalent titanium. The study of the conductivity and the thermoelectric power confirms the classical band model proposed for the rucile structure, involving in this case narrow Π^H bands. The evolution of σ and α as well as that of the c parameter shows that two domains, I and II, must be distinguished, in which the Π^H bands involve the Ti-3d and Nb-4d orbitals, respectively. The first domain is indeed characterized by the presence simultanously of Ti^IV, Ti^III and Nb^V and corresponds to the triangle Ti^IVO₂-Fe^IINb^V₂O₆Ti ^III_0.5Nb^V_0.5O₂ second domain in which all the titanium ions are in the trivalent state is characterized by the presence of Ti^III, Nb^IV and Nb^V simultanously and corresponds to the triangle Nb^IVO₂-Fe^II₂Nb^V₂O₆-Ti^III_0.5Nb^V_0.5O₂.     

Structure de PbU2Se5

PbU₂Se₅ crystallizes in a monoclinic unit cell $\text{a}\text{= 8,605}\text{A}\text{?}$; $\text{b}\text{= 7,788}\text{A}\text{?}$; $\text{c}\text{= 12,27}\text{A}\text{?}$; β = 90° of space group $\text{P}\text{2}{}_1\text{c}$, Z = 4. The crystal structure has been determined for 1251 independant reflections and refined to a final R value of 0,068. Two kinds of uranium sites are found; the average U-Se distances are 2,97 Å for eight-coordination and 2,88 Å in seven-coordination. The average Pb-Se distance for eight-coordination is 3,20 Å. This structure explains the solid solution between PbU₂Se₅ and U₃Se₅.     

Système ternaire La2Se3-Ga2Se3-GeSe2 diagramme de phase — Etude des verres

Existence of a solid solution, hexagonal $\text{Ce}{}_6\text{Al}{}_{\mathrm{<mtext>10</mtext><mtext>3</mtext>}}\text{S}{}_{14}$-type, between $\text{La}{}_6\text{Ga}{}_{\mathrm{<mtext>10</mtext><mtext>3</mtext>}}\text{Se}{}_{14}$ and La₆Ge_2.5Se₁₄ compounds. Location of the eutectic valleys and ternary eutectic (650°C, for La₂Se₃, 3 Ga₂Se₃, 14 GeSe₂). Level curves of the liquidus.Obtention of glasses in a large domain of composition, along the eutectic valley. Measurements of Tg and crystallisation temperature.     

Preparation,properties and crystal structure of TlxV6S8

A new sulfide of vanadium and thallium Tl_xV₆S₈ (x = 0.52±0.2) has been prepared. Its unit cell has hexagonal symmetry, space group P₆₃ and dimensions: $\text{a}\text{= 9.187(7)}\text{A}\text{?}$, $\text{c}\text{= 3.298(4)}\text{A}\text{?}$, z = 1. The structure is characterize by infinite triple rutile chains along the $\text{c}$ axis containing short V-V (2.860 Å) distances. The compound shows metallic behavior.     

Syntheses and magnetic properties of Eu3B2O6 and Sr3B2O6

Europium orthoborate and strontium orthoborate crystallize in the rhombohedral system with two formula units in a cell of dimensions $\text{a}{}_{\mathrm{R}}\text{=6.697}\text{A}\text{?}$, α_R=85.17° for Eu₃B₂O₆, and $\text{a}{}_{\mathrm{R}}\text{=6.695}\text{A}\text{?}$, α_R=85.00° for Sr₃B₂O₆. The equivalent hexagonal lattice parameters are $\text{a}{}_{\mathrm{H}}\text{=9.069}\text{A}\text{?}$, $\text{c}{}_{\mathrm{H}}\text{=12.542}\text{A}\text{?}$, and $\text{a}{}_{\mathrm{H}}\text{=9.046}\text{A}\text{?}$, $\text{c}{}_{\mathrm{H}}\text{=12.566}\text{A}\text{?}$ respectively. Eu₃B₂O₆ appears to be ferromagnetic below 7.5K.     

Some optical and electrical properties of the As2Se3−xTex system

Some optical and electrical properties of the As₂Se_3?xTe_x system (0 ≤ x ≤ 0.15) have been studied. The value of the optical gap decreases from 1.74 eV to 1.59 eV. The slope of the absorption edge changes, so that value of E_o from the relation α ～ exp ($\text{h}\text{?}\text{ω}\text{E}{}_{\mathrm{o}}$) exhibits a maximum value in neighbourhood of composition As₂Se_2.9Te_0.1. The d.c. and a.c. conductivities have been studied. The value of the activation energy E_el ～ 1.8 eV is almost unchanged up to x = 0.15. The a.c. conductivity fulfils the relation $\text{б(ω) ～ ω}{}^{\mathrm{<mtext>s</mtext>}}$ where s ? 1 and 1.1. at frequencies f < 1 kHz and f > 1 kHz respectively.     

The CsTi2NbO7 type layer oxides : Ion exchange properties

The ion exchange properties of the titanoniobate CsTi₂NbO₇ were investigated by action of an acid solution - H₃OTi₂NbO₇.H₂O was thus synthesized leading to H₃OTi₂NbO₇ and HTi₂NbO₇ oxides by dehydratation. The ion exchange ability of H₃OTi₂NbO₇.H₂O allowed to prepare new hydrated compounds : A_1?x(H₃O)_xTi₂NbO₇, yH₂O (A = K, Rb, Tl, Ag), $\text{NH}{}_4\text{Ti}{}_2\text{NbO}{}_7\text{·}\text{1}\text{2}\text{H}{}_2\text{O}$ and A_1?x(H₂O)_1?xH₃O_xTi₂NbO₇, yH₂O (A = Li, Na). The reversibility of the exchanges was observed; the thermal evolution and the crystallographic properties of these exchanged compounds, which are isostructural with CsTi₂NbO₇, were studied and discussed in terms of comparison with the ATiMO₅ structural series.     

The crystal structures of Ba2LaRuO6 and Ca2LaRuO6

Neutron diffraction experiments have been performed to determine the structures of Ba₂LaRuO₆ and Ca₂LaRuO₆. Both are ordered, distorted perovskites. Ba₂LaRuO₆ is monoclinic, space group $\text{P}\text{2}{}_{\mathrm{<mtext>1</mtext>}}\text{n}$ with $\text{a}{}_0\text{=6.0285(7)}\text{A}\text{?}$, $\text{b}{}_0\text{=6.0430(7)}\text{A}\text{?}$, $\text{c}{}_0\text{=8.5409(6)}\text{A}\text{?}$, β=90.44(1)^o. The A sites are occupied by barium and the B sites by an ordered arrangement of lanthanum and ruthenium. Ca₂LaRuO₆ is triclinic, space group P1 with a₀=5.6179(5), b₀=5.8350(5), c⁰=8.0667(4), α=90.0^o, β=89.76(1)^o, γ=90.0^o. The A sites are occupied by calcium and lanthanum in a disordered manner, and the B sites are occupied by an ordered arrangement of calcium and ruthenium. The results reported in this paper thus contradict those of previous workers. The low-temperature magnetic structures are discussed briefly.     

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.     

The role of TiO2 and ZrO2 in Na2OMO2SiO2 glasses

The glass transition temperatures of $\text{(1?x)}\text{Na}{}_2\text{O}\text{·}\text{1}\text{2}\text{x}\text{MO}{}_2\text{·2}\text{SiO}{}_2$ and Na₂O·xMO₂·(2 ?x)SiO₂ glasses, with M = Ti or Zr, have been related to the structural role and coordination of Ti and Zr. The role of network-former, intermediate or modifier of a cation has been fundamentally linked to ionic field strength; T_g values depend on ionic field strength and coordination. Titanium behaves like an intermediate oxide; its coordination ranges between four and six, depending on $\text{Ti}\text{Si}$ ratio. The role of zirconium changes according to the degree of substitution for Na or Si and progressively approaches that of a modifier ion.     

High pressure synthesis of Gd3InO6, Tb3InO6 and Lu3InO6

Three new compounds, X₃InO₆ (X = Gd, Tb, Lu) were prepared at 1–4 GPa, ～1050°C. They are monoclinic, space group $\text{P}\text{2}{}_1\text{n}$ with $\text{a}\text{? 8.9}\text{A}\text{?}$, $\text{b}\text{? 9.8}\text{A}\text{?}$, $\text{c}\text{? 5.9}\text{A}\text{?}$, β ～ 95° and Z = 4.     

Intercroissances des structures de type perovskite et SrO deficitaires en oxygene : Les oxydes Ln2−xSr1+xCu2O6−x/2 (Ln = Sm,Eu, Gd)

New oxides Ln_2?xSr_1+xO_6?x/2 (Ln = Sm, EU, GD), corresponding to oxygen deficient intergrowths of double perovskite and SrO layers have been isolated for 0.70 ≤ x ≤ 0.90. They are characterized by an orthorhombic cell, $\text{a}\text{?}\text{a}{}_{\mathrm{p}}\text{? 3.9}\text{A}\text{?}$, $\text{b}\text{?}\text{3a}{}_{\mathrm{p}}$, and $\text{c}\text{? 20}\text{A}\text{?}$. A structural model has been obtained, showing that this structure, although closely related to that of La_2?xSr_1+xCu₂O_6?x/2+δ exhibits a different distribution of the oxygen vacancies, involving for copper several coordinations. The semi-conductive properties of these compounds, very different from the semi-metallic behaviour of La_2?xSr_1+xCu₂O_6?x/2+δ is explained by the distribution of the oxygen vacancies in the structure.     

Stationary photoconductivity of mixed Tl1−xAgxInSe2 crystals

Tl_1?xAg_xInSe₂ (x = 0 to 0.03) single crystals of solid solution were grown by Bridgeman-Stockbarger techniques. Photoelectric measurements were taken at 300 and 77 K. With an increase in the value of x, the equilibrium concentration is increased 10 to 100 times. At 77 K a region of impurity photosensitivity has been detected which is bordered by the fundamental absorbtion edge. The photosensitivity ($\text{R}{}_{\mathrm{d}}\text{R}{}_{\mathrm{p}}$) of the solid solution crystals at 77 K increases from 8.2 (x = 0) to 55.2 (x = 0.03) the conclusion is made that when Tl is replaced by Ag then the sensitization of semiconductor.     

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.     

Ordering of interstitial nitrogen and oxygen in vanadium near to V8N and V8O

The ordered structure of the V₈N subnitride was studied by X-rays, electron diffraction and electron microscopy. V₈N exists in two different modifications (α′ and α″). The vanadium sublattice of both phases is pseudo-tetragonal, in reality triclinic, with lattice parameters: $\text{α}{}_{\mathrm{<mtext>o</mtext>}}\text{=}\text{b}{}_{\mathrm{o}}\text{= 3.114}\text{A}\text{?}$, $\text{c}{}_{\mathrm{o}}\text{= 2.994}\text{A}\text{?}$, α_o = β_o = 90.5^o ± 0.1^o, γ_o = 90^o. The proposed unit cell of α′-V₈N has dimensions: a = 2√2 a_o, c = 2c_o and corresponds to V₃₂N₄. Doublets of nitrogen atoms occupy two sets of octahedral cavities whose shortest axes are aligned along the x and y directions of the sublattice in an ordered fashion. The α″-V₈N phase is a periodically twinned modification of the α′-V₈N, the twin plane being of the (001) type. The V₈O suboxide has the same structure as the α″-V₈N, the sublattice parameters being: $\text{a}{}_{\mathrm{o}}\text{=}\text{b}{}_{\mathrm{o}}\text{= 3.11}\text{A}\text{?}$, $\text{c}{}_{\mathrm{o}}\text{= 2.994}\text{A}\text{?}$, α_o = β_o = 90.3^o ± 0.1^o, γ_o = 90^o.     

Synthese et caracterisation du pentafluorotellurate (IV) de sodium NaTeF5

Sodium pentafluorotellurate (IV) NaTeF₅ has been prepared by slow evaporation of a $\text{1}\text{1}$ mixture of sodium fluoride and tellurium dioxyde in 50 % aqueous hydrofluoric acid.NaTeF₅ has an orthorhombic structure, parameters of which are $\text{a}\text{= 9.10}{}_5\text{A}\text{?}$$\text{b}\text{= 11.30}{}_6\text{A}\text{?}$$\text{c}\text{= 10.12}\text{A}\text{?}$     

Copper doped zinc oxide Y2BaZnO5: ERS and optical investigation

In copper doped Y₂BaZnO₅ oxides, copper exhibits a distorted square pyramidal coordination which is consistant with the values of g and A tensors obtained from O band ERS spectrum for a sample containing about 1 % Cu. Three values for g and A are observed, g₁ = 2.049₅, g₂ = 2.051₅, g₃ = 2.275, $\text{¦}\text{A}{}_1\text{¦ = 13 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$, $\text{¦}\text{A}{}_2\text{¦ = 10 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$ and $\text{¦}\text{A}{}_3\text{¦ = 147.5 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$. Since $\text{g}{}_1\text{?}\text{g}{}_2$ an approximate C_4v point symmetry can be assumed for copper. The electronic spectrum shows three bands at 11700, 14500 and 20500 cm^?1 which can be assigned to the transitions A₁ → B₁, B₂ → B₁ and E → B₁ respectively. The orbital reduction parameters are calculated and the bonding covalency is discussed.