Les intercalaires Ax Ti S2 et Ax Zr S2. Structure et liaisons. (A = Li,Na, K,Rb, Cs)

A general survey of alkali metals intercalation compounds with titanium and zirconium disulfides is given. A model A⁺_x (Ti S₂^x? or A⁺ (Zr S₂)^x? with an electronic delocalization in the (Ti²S₂) or (Zr S₂) slabs, is suggested according to crystallographic and magnetic studies, N.M.R. measurements, and chemical behaviour. The alkali metal coordination is related to several factors: size of the A⁺ ion, value of the x parameter, strength of the T.S. bonds.     

New compounds A2−xV8O16 (A = K,Tl) with hollandite type structure

K₂V₈O₁₆, K_1.8V₈O₁₆ and Tl_1.74V₈O₁₆ were synthesized by high pressure- high temperature treatment of KVO₃ and TlVO₃ in a modified Belt-type apparatus. The compounds crystallize tetragonal, space group I4/m. They are the first well-characterized Vanadium-hollandites and show a remarkable high occupation of the tunnel sites with univalent cations.     

AB2F7 phases in the systems AF BF3 (A = K,Rb, Cs,Tl; B = In,Tl, Ln)

KY₂F₇ and KGd₂F₇ are monoclinic, space group I2, Im or I2/m. α-RbGd₂F₇ and α-CsGd₂F₇, on the other hand, are orthorhombic, space group possibly Pbnn. KIn₂F₇ and TlTl₂F₇ are monoclinic, space group Pm or P2. KTl₂F₇ is orthorhombic, space group probably Pnnn. The packing efficiency increases in the sequence α-RbGd₂F₇ type (as well as KIn₂F₇ type) - TlTl₂F₇ type - KY₂F₇ type.     

Sur de nouveaux pyrochlores ASbWO6 (A = K,Rb, Cs,Tl)

New compounds ASbWO₆ of pyrochlore type with A = K, Rb, Cs, Tl were isolated. The positions of the A cations in the cubic cell were determined and discussed.     

P4O8(WO3)2m: A series of phosphate tungsten bronzes characterized by empty pentagonal tunnels

A new series of phosphate tungsten bronzes P₄O₈(WO₃)_2m has been investigated by X-ray and electron diffraction and electron microscopy. The structure of these phases is derived from that of P₄W₈O₃₂ which corresponds to the fourth member of the series: it is thus built up from ReO₃ type slabs separated by planes of PO₄ tetrahedra forming empty pentagonal tunnels. The electron diffraction and microscopy study of the integral m compositions has shown the existence of the different members of the series, ranging from m = 4 to 16, in the form of pure ordered microcrystals. Most of the members of the series except m = 5 are characterized by an orthorhombic cell related to that of ReO₃ in the following way:

     

Phase equilibria in the Zn2P2O7-M2ZnP2O7 and M′2ZnP2O7-M″2ZnP2O7 (M, M′, M″ = Li, Na, K) glass-forming systems

Data are presented on the phase relations in the Zn₂P₂O₇-M₂ZnP₂O₇ and M′₂ZnP₂O₇-M″₂ZnP₂O₇ (M, M′, M″ = Li, Na, K) systems. The stable and metastable phase equilibria in these systems have been investigated, new compounds have been identified, and wide solid-solution ranges have been found. Some of the physicochemical properties of the synthesized phases are described. Original Russian Text ? M.A. Petrova, G.A. Mikirticheva, R.G. Grebenshchikov, 2007, published in Neorganicheskie Materialy, 2007, Vol. 43, No. 9, pp. 1141–1148.     

A2BF5 phases in the systems AF-BF3 (A=K,Rb, Cs,Tl; B=Al,Fe, Cr,Ga, V,Tl, Ln)

A phase previously reported to be α-K₃GdF₆ is in fact a mixture of K₂GdF₅ and KF. K₂GdF₅ possesses the K₂SmF₅ structure. Rb₂GaF₅ and K₂GaF₅ possess the Rb₂CrF₅ and K₂CrF₅ structures, respectively. A phase reported to be Tl₂Tl³⁺F₅ is monoclinic, space group I2, Im or 12/m with $\text{a}\text{=4.176,}\text{b}\text{=6.336,}\text{c}\text{=4.110}\text{A}\text{?}\text{, β=111.4°}$. The K₂SmF₅, Rb₂CrF₅ and K₂CrF₅ structures are compared, and predictions are made as to further members of these structural groups.     

Phase relations in the systems A2TeI6-Tl2TeI6 (A = K, Rb, Cs) and A2TeBr6-A2TeI6 (A = K, Rb, Cs, Tl(I))

Phase relations in the systems K₂TeI₆-Tl₂TeI₆ (I), Rb₂TeI₆-Tl₂TeI₆ (II), Cs₂TeI₆-Tl₂TeI₆ (III), K₂TeBr₆-K₂TeI₆ (IV), Rb₂TeBr₆-Rb₂TeI₆ (V), Cs₂TeBr₆-Cs₂TeI₆ (VI), and Tl₂TeBr₆-Tl₂TeI₆ (VII) are studied. System VI contains a continuous series of solid solutions, while the other systems have eutectic phase relations with rather broad solid-solution ranges. The relationship between the ionic radii of A⁺ and Hal^- (Hal = Br, I) is shown to play a key role in determining the structure type of the A₂TeHal₆ compounds and the phase relations in the systems studied.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 357–362.Original Russian Text Copyright © 2005 by Peresh, Sidei, Zubaka.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Sur les proprietes magnetiques des bronzes fluores de vanadium MxVF3α (M = K,Rb, Cs)

The magnetic properties of the α-M_xVF₃ fluorides have been investigated from 4.2 to 550 K. An antiferromagnetic behavior has been observed, the Néel temperature being in each case close to 18 K for x = 0.25. Below the ordering point a weak ferromagnetic component appears, which decreases sharply from potassium to cesium. This behavior is compared with that of the VF₃ fluoride and of the homologous α-M_xFeF₃ phases (M = K, Rb, Cs).     

Two new barium indium phosphates with intersecting tunnel structures: BaIn2P4O14, and Ba3In2P4O16

Two new barium indium phosphates BaIn₂P₄O₁₄ and Ba₃In₂P₄O₁₆ were synthesized by high temperature solution growth method and structurally characterized by single crystal X-ray diffraction analysis. They represent first compounds in the Ba-In-P-O systems. BaIn₂P₄O₁₄ and Ba₃In₂P₄O₁₆ display different types of 3D architectures. The projections of both structures concern about the existence of the intersecting tunnels. In compound BaIn₂P₄O₁₄, the tunnels are built up of the corner-sharing InO₆ octahedra and P₂O₇ groups, whereas in compound Ba₃In₂P₄O₁₆, they are formed by corner sharing of PO₄ tetrahedra and InO₆ octahedra. The electronic band structure calculations of two compounds have been performed with the density functional theory method. The study of calculations and optical diffuse reflectance experimental results show both compounds are insulators with direct band-gap.     

Syntheses and physical properties of pyrochlore-type A2B2O7 (A=Tl,Y; B=Cr,Mn)

Pyrochlore-type A₂B₂O₇ (A=Tl,Y; B=Cr,Mn) were synthesized under conditions of elevated temperature and pressure up to 1100°C and 9GPa. Magnetic measurements indicate that the transition metals in the compounds are tetravalent and Tl₂Mn₂O₇ is ferromagnetic with the Curie temperature at 117K. Electric measurements show that Tl₂Mn₂O₇ is a semiconductor with a resistivity maximum at temperatures near the magnetic transition point but other compounds possess high resistivity of the order of 10⁸Ω·cm.     

Cs8V1,1W13,9O48, ein oxid mit einer vom pyrochlortyp abgeleiteten schichtstrukturCs8V1.1W13.9O48, an oxide with a layer structure derived from the pyrochlore type

The title compound crystallizes monoclinically with a = 1257.8(2), b = 726.6(1), c = 2489,3(5) pm, ß = 99,7(1)^o in a layer structure. The layers are formed by ordered vacancies in the B₂O₆ octahedral network of the defect pyrochlor type structure AB₂O₆.     

Crystal structure of rhombohedral MCd(NO2)3 [M = K, Rb, Cs, Tl] from X-ray powder diffraction data

Crystal structure of double nitrites MCd(NO₂)₃ [M=K, Rb, Cs, Tl] at room temperature was ab initio determined from X-ray powder diffraction data. The compounds are isostructural and can be described as rhombohedrally distorted perovskites: space group R3 (no. 146); Z=1; M=K: a=7.5887(1), c=9.1285(2) Å; M=Rb: a=7.6290(1), c=9.2355(2) Å; M=Cs: a=7.7305(1), c=9.4170(3) Å; M=Tl: a=7.6219(1), c=9.2300(2) Å. The coordination polyhedra of cadmium and M cations are the distorted tricapped trigonal prism [(3O+3N)+3O] and cuboctahedron, respectively.     

Crystal structure and ionic conductivity of ruthenium diphosphate ARu2(P2O7)2, A=Li, Na, and Ag, with a tunnel structure

Crystal structure and ionic conductivity of ruthenium diphosphates, ARu₂(P₂O₇)₂ A=Li, Na, and Ag, were investigated. The structure of the Ag compound was determined by single crystal X-ray diffraction techniques. It crystallized in the triclinic space group P−1 with a=4.759(2) Å, b=6.843(2) Å, c=8.063(1) Å, α=90.44(2)°, β=92.80(2)°, γ=104.88(2)°, V=253.4(1) Å³. The host structure of it was composed of RuO₆ and P₂O₇ groups and formed tunnels running along the a-axis, in which Ag⁺ ions were situated. The ionic conductivities have been measured on pellets of the polycrystalline powders. The Li and Ag compounds showed the conductivities of 1.0×10⁻⁴ and 3.5×10⁻⁵ S cm⁻¹ at 150 °C, respectively. Magnetic susceptibility measurement of the Ag compound showed that it did not obey the Curie-Weiss law and the effective magnetic moment decreased as temperature decreased due to the large spin-orbital coupling effect of Ru⁴⁺ ions.     

New palladium phosphate complexes: K2PdP2O7 and K3.5Pd2.25(P2O7)2 synthesis, single crystal structure and conductivity

Two new diphosphate complexes containing potassium and palladium, K₂PdP₂O₇ and K_3.5Pd_2.25(P₂O₇)₂, have been synthesized and characterized by single crystal X-ray diffraction. K₂PdP₂O₇ exists with layers formed of linked PdP₂O₇ polyhedra, between which are found the potassium ions. K_3.5Pd_2.25(P₂O₇)₂ with a Pd/P₂O₇ ratio of 1.125:1 crystallizes with tunnels of various sizes in which are found the potassium ions. Conductivity measurements reveal the material to be conducting.     

Syntheses of hollandite type Rb2Cr8O16, K2Cr2V6O16 and K2V8O16

Hollandite-type compounds, Rb₂Cr₈O₁₆, K₂Cr₂V₆O₁₆ and K₂V₈O₁₆, were synthesized under high P-T conditions up to 1200°C and 7GPa. The structural refinement using a single crystal of Rb₂Cr₈O₁₆ confirms that the structure is similar to that of K₂Cr₈O₁₆. Magnetic measurements indicate that Rb₂Cr₈O₁₆ is ferromagnetic below 295K, K₂Cr₂V₆O₁₆ paramagnetic down to 77K and K₂V₈O₁₆ has susceptibility anomaly at 175K. These compounds are all semiconductive and show discontinuities in temperature-resistivity curves at points corresponding to magnetic anomalies.     

Luminescent properties of Sr2P2O7:Eu,Mn phosphor under near UV excitation

The phosphors in the system Sr_2−x−yP₂O₇:xEu²⁺,yMn²⁺ were synthesized by solid-state reactions and their photoluminescence properties were investigated. These phosphors have strong absorption in the near UV region, which is suitable for excitation of ultraviolet light emitting diodes (UVLEDs). The orange-reddish emission of Mn²⁺ in these phosphors can be used as a red component in the tri-color system and may be enhanced by adjusting the Mn²⁺/Eu²⁺ ratio. The energy transfer from Eu²⁺ to Mn²⁺ is observed with a transfer efficiency of ∼0.45 and a critical distance of ∼10 Å. The results reveal that Sr_2−x−yP₂O₇:xEu²⁺,yMn²⁺ phosphors could be used in white light UVLEDs.     

Mode de formation et stabilite des phases AnBnO3n+2 mises en evidence dans les systemes La2Ti2O7 - CaTiO3, Nd2Ti2O7 - CaTiO3 et Ca2Nb2O7 - CaTiO3

The stability of the A_nB_nO_3n+2 phases, whose structure is derived from the perovskite structure, was investigated through X-Ray diffraction, in the following systems: La₂Ti₂O₇ - CaTiO₃, Nd₂Ti₂O₇ - CaTiO₃ and Ca₂Nb₂O₇ - CaTiO₃. Some of the phases quenched from the liquid are metastable and include vacancies overA and B sites. A model of formation of these phases is proposed.     

Les niobates CaUNb2O8 et MThNb2O8 (M = Ca,Sr, Cd). Etude des transformations monoclinique - quadratique

New compounds M^IIThNb₂O₈ with M^II = Ca, Sr, Cd, and CaUNb₂O₈ have been prepared by solid state reaction. These compounds isotypic with the rare-earth niobates LnNbO₄ cristallize in a monoclinic system with space group I2/c. Like the niobates LnNbO₄, they present a displacive and non quenchable transition (monoclinic to tetragonal) which is probably of second order.