Zu dem Transportsystem V-O-Te-Cl und dem Transportverhalten der Vanadinoxide mit TeCl4(II). Der chemische Transport der Magnéliphasen VnO2n–1, des V6O13 und des V2O5

It was reported on the transport system V O Te Cl and on the transport behaviour of VO₂ in a previous paper. This paper deals with the chemical transport of Magnéli phases V_nO_2n–1, and of V₆O₁₃, and of V₂O₅. Resulting from the composition of the gas phase over the solid phases in the presence of TeCl₄ the chronological sequence of the transported phases as well as the direction and rate of transport are calculated. These results are compared with experiments. All of the oxides are obtained without deposition of any other phases. Their phase boundaries are determined. The dependence on temperature is investigated for the upper phase boundary of V₂O₃.     

Structure of V2O5–P2O5 glasses by X-ray and neutron diffraction

The atomic structures of two V₂O₅–P₂O₅ glasses and vitreous (v-) V₂O₅ were investigated by X-ray and neutron diffraction. The V=O double bond is a common characteristic of the VO_n units that constitute the structures of the glasses. VO₅ square pyramids with elongated bonds of ~ 0.190 nm to the pyramidal base are found for the 50V₂O₅–50P₂O₅ glass. These weaker V–O bonds are balanced in V–O–P bridges by overbonded P–O bonds. The V^(IV) sites, which account for 19.7% and 35.2% of the total V sites in the 73V₂O₅–27P₂O₅ and 50V₂O₅–50P₂O₅ glasses, respectively, form similar pyramids in agreement with the structure of crystalline (VO)₂P₂O₇. The short-range structure of v-V₂O₅ and the 73V₂O₅-27P₂O₅ glass is formed of mixtures of VO₅ and VO₄ pyramids. A significant amount of V···O distances > 0.22 nm found for all glasses belong either to linkages V=O···V or to three-coordinated O sites.     

Characterization of nanocrystals in laser condensates deposited through vanadium evaporation in an oxygen atmosphere

The influence of the substrate temperature T _sub (20–360°C) and the oxygen pressure P(O₂) (5 × 10⁻³−0.13 Pa) in an evaporation chamber on the structure and phase composition of films prepared through laser sputtering of a vanadium target is investigated by electron diffraction and in situ transmission electron microscopy (with the use of the bend extinction contour technique for determining the bending of the crystal lattice). It is demonstrated that the oxygen content in the films increases with an increase in the oxygen pressure P(O₂) at a fixed substrate temperature T _sub and decreases with an increase in the substrate temperature T _sub at a fixed oxygen pressure P(O₂). The conditions responsible for the formation and composition of the crystalline (VO_0.9) and amorphous (V₂O₃) phases in the films are determined. It is established that the phase composition of the film depends on the angle of condensation of the vapor-plasma flow. The crystallization of the V₂O₃ amorphous phase is accompanied by an increase in the density by 9.2%. It is revealed that the V₂O₃ spherulites growing in the amorphous film have a bent crystal lattice. The bending of the crystal lattice can be as large as ∼42 deg/μm.

     

Structural features of compounds of the sillenite family

It is shown that the real composition and structure of phases belonging to the sillenite family can be determined using a complex of techniques (diffraction methods, vibrational and X-ray absorption spectroscopy, and electron probe X-ray microanalysis) with a subsequent crystal-chemical analysis of the data. Refined compositions are presented for phases of nominal composition Bi₂₄ M ₂O₄₀ with M = Zn²⁺, Al³⁺, Ga³⁺, Fe³⁺, Si⁴⁺, Ti⁴⁺, Mn⁴⁺, and P⁵⁺, which demonstrate types and concentrations of point defects as functions of the M type.     

Two Metal Complexes Supported by {VO<Subscript>3</Subscript>}<Subscript>n</Subscript><Superscript>n−</Superscript> Chains: Hydrothermal Syntheses and Crystal Structures of [M(dpa)V<Subscript>2</Subscript>O<Subscript>6</Subscript>] (M = Zn(II) and Cu(II); dpa = 2,2′-dipyridylamine)

Abstract  

Two new metal complexes supported by {VO₃}_n ⁿ⁻ chains, [M(dpa)V₂O₆] (1, M = Zn²⁺; 2·H₂O, M = Cu²⁺; dpa = 2,2′-dipyridylamine), have been synthesized hydrothermally and characterized by elemental analysis, TG analysis, IR spectroscopy and single-crystal X-ray diffraction. Crystal data: [Zn(dpa)V₂O₆] 1, Triclinic, P-1, a = 9.663(7) ?, b = 10.617(7) ?, c = 15.114(10) ?, α = 105.678(10)°, β = 104.772(9)°, γ = 94.021(10)°, Z = 2; [Cu(dpa)V₂O₆]·H₂O 2·H₂O, Monoclinic, C2, a = 20.543(3) ?, b = 7.2460(9) ?, c = 10.4853(13) ?, β = 111.318(2)°, Z = 4. Complex 1 is constructed from sinusoidal {VO₃}_n ⁿ⁻ chains with {Zn(dpa)}²⁺ fragments spanning the adjacent troughs and crests into an 1D ribbon-like structure. Complex 2 is built up by linking {VO₃}_n ⁿ⁻ chains via pairs of symmetrical {Cu(dpa)}²⁺ fragments into a 2D layered structure. The Zn(II) and Cu(II) ions exhibit tetrahedral and square pyramidal coordination environments, respectively. The formation of the two isomers is attributed to the flexibility of {VO₃}_n ⁿ⁻ chains and the different coordination configurations of the two metal ions. There exist significant π–π stacking and hydrogen bonding interactions in complexes 1 and 2.     

Vanadium contribution in different glasses in view of the ligand field theory

Spectrophotometric and magnetic studies were carried out on different glasses containing known amounts of V₂O₅ in order to throw some light on the valence states and coordination of vanadium in such glasses (in view of the ligand field theory).The results obtained were found to be in agreement with those of aqueous solutions, e.g. [V(H₂O)₆]³⁺, [VO(H₂O)₅]²⁺, and VO²⁺ which showed a slight difference in band positions due to the distortion as well as the difference between the ligand field strength of glass and water. Generally it may be concluded that vanadium is present in borate and silicate glasses in three possible valencies, V⁵⁺, V⁴⁺ and V³⁺, while in phosphate glasses it is generally present in two valencies V⁴⁺ and V³⁺.     

Electronic conductivity and structural chemistry in Li-Te-V oxide glasses

The electronic conductivity of the Li₂O-Te₂V₂O₉ glass system reveals that, even for high lithium content, electron hopping occurs between V⁴⁺ and V⁵⁺. The study of the V⁴⁺ content versus various syntheses shows that more than lithium content, the nature of the counter ion used in Li⁺ reagent and its decomposition behavior are responsible for the efficiency of the spontaneous V⁵⁺ reduction via a ‘sprouting’ phenomenon. The electron hopping process implies interconnection of VO_n polyhedra which are accessible for both V⁴⁺ and V⁵⁺ species. Such fact gives information about short and medium range ordering in the glasses. On the basis of the LiVTeO₅ crystal structure and in agreement with wide angle X-ray scattering experiments, a possible rearrangement bringing together VO₅ square pyramids is proposed to explain the electron hopping. Such proposal corresponds to a lithium network forming effect. It could explain why for Li/V>1 the electronic conductivity increases with lithium content while the V⁴⁺ amount remains low.     

Magnetic behavior and microstructure of x%V2O5·(100−x)%As2O3 glasses

The magnetic properties and microstructure of x%V₂O₅·(100−x)%As₂O₃ glasses with x varying in the range 40 to 90 mol% were investigated in order to elucidate their magnetic ordering. Weak antiferromagnetic interactions between V⁴⁺ ions were observed. Glasses with x ⩾ 60 separated into two glassy phases. The effect of microstructure on magnetic properties of these glasses was investigated. Phase separation increases with increasing V₂O₅ content and produces a broadening of the EPR line width of glasses with high vanadium content (x > 70). The c = V⁴⁺/V_total ratio of x%V₂O₅·(100−x)%As₂O₃ glasses, determined from EPR and chemical analysis, are considerably greater than those usually reported for x%V₂O₅·(100−x)%P₂O₅ glasses.     

Effect of V2O5 addition on the crystallisation of glasses belonging to the CaO–ZrO2–SiO2 system

The crystallisation of CaO–ZrO₂–SiO₂ glasses doped with V₂O₅ (0.1–5 mol%) has been investigated in terms of microstructure and thermal parameters. Results indicate that crystallisation is predominantly controlled by a surface nucleation mechanism, even though a partial bulk nucleation has been encountered in compositions containing more than 2 mol% of doping oxide. As detected from differential thermal analysis curves, glass transition temperature and crystallisation temperature, are strongly dependent upon V₂O₅ content varying from 0.0 to 2.0 mol%, while the crystallisation activation energy values decrease with a parabolic trend from B-glass (0.0 mol% V₂O₅ content, 495±7) to V-0.7 (0.7 mol% V₂O₅ content, 420±6) composition, increasing again to 442±5 kJ/mol K with higher amount of V₂O₅. The microstructure of the glass-ceramic materials clearly showed a marked dependence upon the amount of V₂O₅, also due to the presence of phase separation for content higher than 0.7 mol%. Wollastonite, CaO·SiO₂, and a calcia–zirconia–silicate, 2CaO·4SiO₂·ZrO₂, are the main crystalline phases whose ratio slightly varies with vanadium oxide content. The glass ceramics obtained from the studied materials are greenish and bluish coloured, so it is possible to use the studied glasses as coloured frits for tile glazes.     

A square-wave voltammetric study on the diffusivities of polyvalent elements in CaO/BaO/Al2O3/SiO2 glass melts

Diffusion coefficients of various polyvalent ions (Sn²⁺, As³⁺, As⁵⁺, Sb³⁺, Sb⁵⁺, Cr³⁺, Ti⁴⁺, V⁴⁺, V⁵⁺ and Fe³⁺) were measured in melts with the basic compositions of 10CaO·10 BaO·10Al₂O₃·70SiO₂ and 10CaO·10BaO·15Al₂O₃·65SiO₂ by means of square-wave voltammetry. At temperatures in the range of 1300-1600 °C, linear correlations between logD and 1/T were observed. At 1400 °C, the diffusion coefficients obtained are compared with those obtained from other glass melt compositions.     

On the bindings in the crystal phases of Mn

The heterotypism of Mn may be interpreted energetically when a temperature dependent valence electron concentration is supposed which takes on values between 2.2 and 0.6 electrons per atom. The room temperature phase Mn.r (= αMn) belongs to a series of structural types: Cr₃Si, U.h₁ (= βU), Mn.r, which occur in alloy systems such as MoRe_M (M = undetermined mole number) at certain values of the averaged group number (AGN) of the perodic system of chemical elements (rule of Raub). An interpretation of the series by means of the plural-correlations model becomes possible when instead of the (Ekmanian) AGN count another (non-Ekmanian) electron count is used. The phase Mo₃Re (Cr₃Si-type) yields a simple bonding type (binding) which undergoes moderate transformations to form the phases Mo₂Re₃(U.h₁) and MoRe₃(Mn.r) and the binding of MoRe₃ may be taken to be valid also for Mn.r; it corresponds to the valence electron concentration N′^A_b = 2.16. For the high temperature phases Mn.h₁ (= βMn) and Mn.h₂ (= γMn) the values N′^A_b = 1.6 and 1.0 are probable and allow the brass-like structures Mn.h₁ (C20) and Cu(Fl). The binding of Mn.h₂, incidentally, explains the occurrence of the tetragonal metastable phase Mn.m. finally Mn.h₃ (= δMn) crystallizing in the W-type is isodesmic to Fe.h₂ (= δFe), i.e. of the same binding.     

Crystal structure of [Rb0.24(H2O)0.76]VO(H2O)(PO4), a new monoclinic variety in the series of layered vanadyl phosphates

The crystal structure of a new monoclinic variety of hydrous rubidium vanadyl phosphate [Rb_0.24(H₂O)_0.76]VO(H₂O)(PO₄) doped with Al³⁺ ions is studied by X-ray (R = 0.054) diffraction: a = 6.2655(4) Å, b = 6.2712(3) Å, c = 6.8569(5) Å, β = 107.805(7)°, space group P2₁/m, Z = 2, and D _x = 2.792 g/cm³. The new phase obtained by the hydrothermal synthesis in the V₂O₅-Rb₂CO₃-AlPO₄-H₂O system has a layer-type structure in which Rb atoms and water molecules are located between layers of vertexsharing [VO₅(H₂O)] octahedra and [PO₄] tetrahedra. Rb intercalates based on VOPO₄ · 2H₂O are described by general formula [Rb _x (H₂O)_{1 ? x} ]V _1?x ^V V _x ^IV O(H₂O)(PO₄), where x ≤ 0.5, and the amount of reduced vanadium and interlayer water molecules is determined by the amount of introduced rubidium atoms.     

Crystal growth of mixed‐valence ammonium vanadates

A new method has been developed for the synthesis of mixed‐valence ammonium vanadate crystals. Single crystals of (NH₄)₂V₃O₈ were synthesized on a large scale by hydrothermal reduction of NH₄VO₃ in ethanol‐H₂O solutions in the presence of triblock copolymer Pluronic P123. The crystals are shining thin plates with (001) cleavage planes. Calcination of the (NH₄)₂V₃O₈ crystals at 300°C or above resulted in pure phases of V₂O₅. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Some features of EPR and optical spectra of vanadium in aluminophosphate glasses

The EPR and optical spectra of vanadium in glasses of ternary Al₂O₃P₂O₅SiO₂ and Al₂O₃P₂O₅B₂O₃ systems have been measured. The results were compared with earlier data for vanadium in binary phosphate, aluminophosphate and silicaphosphate glasses and with results of de-Biasi for V⁴⁺ in crystalline powder α-crystobalite AlPO₄. The superpositions of two hyperfine spectra (ASB-I and ASB-II) were found for many glasses of ternary systems. Both spectra can be attributed to VO²⁺ ions. The intensity ratio of the ASB-II spectrum to ASB-I depends on glass composition but is great (> 7) for all the glasses. Only the ASB-II spectrum was observed in glasses with low concentration of Al₂O₃. The spectral parameters of ASB-II spectrum are g_| = 1.916–1.921; g_⊥ 1.980–1.988; A_| = (188?190) × 10^?4cm^?1 and A_⊥ = (74–77) × 10^?4cm^?1. Three intense bands at 370, 455 and 700 ans 720 nm observed in these glasses can be attributed to V³⁺ ions. The excellent agreement of the parameters of the EPR spectrum of V⁴⁺ ions in crystalline α-crystobalite AIPO₄ and ASB-II spectra in the glasses under study suggest the identical electron structure of the paramagnetic species. This species is believed to be characterized by optical bands at 680 and 790 nm which have been observed by de Biasi. The orbital mixing coefficients indicate strong tetragonal distortion of vanadyl complexes responsible for the ASB-II spectrum. It is assumed that VO²⁺ ions responsible for this spectrum act as modifiers fitting into the relatively small holes of the three-dimensional networks of phosphate glasses containing no cations of large radii. The microscopic basicity of oxygens in such holes must be about 0.48.     

Hydrothermal crystallization in the NaOH-GeO2-H2O system at 350°C: Mechanism of self-assembly of subpolyhedral clusters in Na4Ge

The Na,Ge^[6]-germanates of the compositions Na₄Ge ₄ ^[6] Ge ₅ ^[4] O₂₀ and Na₃HGe ₄ ^[6] Ge ₃ ^[4] O₁₆ · 4H₂O are crystallized in the NaOH-GeO₂-H₂O system under a pressure of 0.05 GPa and a temperature of 350°C. The structure of the germanates consists of open frameworks of M octahedra (Ge^[6]) and T tetrahedra (Ge^[4]). With an increase in the NaOH concentration, the crystallization fields change in the sequence R-GeO₂ (rutile structure type) ⇒ R-GeO₂ + Na₄Ge ₄ ^[6] Ge ₅ ^[4] O₂₀ ⇒ Na₄Ge ₄ ^[6] Ge ₅ ^[4] O₂₀ + Na₃HGe ₄ ^[6] O₁₆ · 4H₂O ⇒ Na₃HGe ₄ ^[6] Ge ₃ ^[4] O₁₆ · 4H₂O. The phase formation for Na,Ge^[6] germanates and Na,Ti silicates (Na₄Ti ₄ ^[6] Si ₃ ^[4] O₁₆ · 6H₂O and NaHTi ₂ ^[6] O₇ · 2H₂O) is considered based on the model of the matrix assembly of crystal structures from invariant Ge^[6],Ge^[4] subpolyhedral structural units. The homologous family of phases consisting of Na₄Ge ₄ ^[6] Ge ₅ ^[4] O₂₀ (M ₄ T ₅ framework), Na₃HGe ₄ ^[6] Ge ₃ ^[4] O₁₆ · 4H₂O, Na₄Ti ₄ ^[6] Si ₃ ^[4] O₁₆ · 6H₂O (M ₄ T ₃ framework), and NaHTi ₂ ^[6] Si^[4]O₇ · 2H₂O (M ₄ T ₂ framework) phases with topologically equivalent one-dimensional MT structures is singled out. __________ Translated from Kristallografiya, Vol. 48, No. 5, 2003, pp. 950–958. Original Russian Text Copyright ? 2003 by Ilyushin, Dem’yanets. Dedicated to the 60th Anniversary of the Shubnikov Institute of Crystallography of the Russian Academy of Sciences     

Crystal structure of double vanadates Ca9 R(VO4)7. II. R = Tb, Dy, Ho, and Y

Crystal structures of the compounds Ca₉ R(VO₄)₇ (R = Tb (I), Dy (II), Ho (III), and Y (IV) have been studied by the method of the full-profile analysis. All the compounds are crystallized in the trigonal system (sp. gr. R 3 c, Z = 6) with the unit-cell parameters (I) a = 10.8592(1), c = 38.035(1), V = 3884.2(2) ų; (II) a = 10.8564(1), c = 38.009(1) Å, V = 3879.6(2) ų, (III) a = 10.8565(1) and c = 37.995(1) Å, V = 3878.3(2) ų, and (IV) a = 10.8588(1), c = 37.995(1) Å, V = 3879.9(2) ų. In structures I–IV, rare earth and calcium cations occupy three positions—M(1), M(2), and M(5). Rare earth cations occupy the R ³⁺ positions almost in the same way: 2.7–2.6(2) cations in the M(1) position; 2.7–2.3(2) cations in the M(2) position, and 0.6–1.0(1) cation in the M(5) position. At the same time, the occupancy of the M(5) position regularly increases with a decrease of the R ³⁺ radius.     

Darstellung von VO2-einkristallen der oberen und unteren phasengrenze durch chemischen transport

The chemical transport of VO₂ with TeCl₄ was investigated in the temperature range of about 1000°C and 600°C. In the first case there is TeO₂ existing in the gaseous phase, in the second case the TeO₂ has no noticeable vapour pressure. The transport takes place from the hot to the cool zone. In both cases we obtained high transport rates of 10 to 20 mg h^-1. The composition of the gaseous phase is calculated and the transport mechanisms are discussed. It is possible to obtain VO₂ with the upper and lower phase boundary by variation of the initial compositions. Starting with compositions lower than VO_1.99 we obtained near 1000°C in the deposition zone V₈O₁₅ first and after a time VO₂ with the lower phase boundary. Compositions higher than VO_2.00 give vanadium dioxide with the upper phase boundary. In the temperature range of about 600°C however we obtained the phase with the higher oxygen content first. The results are compared with those, which have been obtained by the transport of VO₂ with HCl and Cl₂ — which takes place from the cool to the hot zone.     

Phase composition,microstructure and conductivity of (85-α)VO2–15(Vanadium–Phosphate–Glass)–αCu glass–ceramics

Electric conductivity, microstructure and phase composition of (85-α)VO₂–15VPG–αCu glass–ceramics (VPG = Vanadium–Phosphate–Glass) with copper content in the interval 0 wt% ⩽ α ⩽ 15 wt% were investigated. VPG is the glass (molar %) 80V₂O₅–20P₂O₅. Only two phases: VO₂ and VPG were identified when α ⩽ 5 wt%. VO₂ crystallites, VPG and pores are observed in these ceramic microstructures. Glass forms layers 1–2 μm thick in the space between VO₂ crystallites. The copper is dissolved in VPG during glass–ceramic synthesis. It increases the electric conductivity of the glass and provides improvement of electrical bonds between VO₂ crystallites. Therefore glass–ceramics conductivity exhibits an abrupt change of approximately 100× in the vicinity of the phase transition temperature, T_t, in VO₂. A new crystalline phase appears in (85-α)VO₂–15VPG–αCu ceramics when α ∼ 6 wt%. This phase is observed as small crystallites with the sizes of 1–5 μm. The increase in such phase content, with an increase in copper content is accompanied by a decrease in the content of VO₂. Percolation along the new phase is a primary contributor to electric conductivity when α ⩾ 8 wt%. In this case the conductivity exhibits no abrupt change in the vicinity of the temperature T_t. The new phase is probably the bronze Cu_xV₂O₄. It crystallizes from a liquid phase during glass–ceramics synthesis.     

Vanadyl ion stability in silica gels

Silica gels doped with vanadium were prepared from tetra ethyl orthosilicate and an aqueous solution of NH₄VO₃, at a final sol pH of 1.5–2.5. Absorption and electron paramagnetic resonance (EPR) spectral studies establish that under ambient conditions the incorporated pentavalent vanadium is stabilized as tetravalent vanadyl ion in the gel monoliths. Dried gels were very stable under ambient conditions, however, transformation of V⁴⁺ to V⁵⁺ was noted during gel densification.     

Synthesis,crystal structure and vibrational characterization of bis‐μ‐peroxo‐hexacarbonatodicerate(IV) complexes of rubidium and cesium

The new compounds Rb₈[Ce(O₂)(CO₃)₃]₂ · 12 H₂O (1) and Cs₈[Ce(O₂)(CO₃)₃]₂ · 10 H₂O (2) were obtained from the reaction of hydrogen peroxide and Ce(III) in saturated alkali carbonate solutions. The crystal structures and the unit cell parameters of (1) triclinic, P‐1 with a = 8.973(2) Å, b = 10.815(2) Å, c = 11.130(3) Å, α = 66.992(2)°, β = 68.337(2)°, γ = 74.639(2)°, V_EZ = 914.7(4) ų, Z = 2, and (2) orthorhombic, Pbca, a = 19.3840(16) Å, b = 18.528(2) Å, c = 10.487(3) Å, V_EZ = 3766.4(13) ų, Z = 8, were determined. Both compounds contain the bis‐µ‐peroxo‐hexacarbonatodicerate(IV)‐ion, [(CO₃)₃Ce(O₂)₂Ce(CO₃)₃]^8‐. IR and Raman spectra were measured and discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)