Studium der Reaktionen von TlNO3-V2O5 in Fester Phase

The solid-state reactions of TlNO₃ with V₂O₅ in the molar ratios of 6∶5 and 2∶3 were studied by DTA, DTG and TG in the temperature ranges 20–550° and 20–400°, respectively, in a nitrogen atmosphere. For the molar ratio of 6∶5, thallium pentavanadate (Tl₃V₅O₁₄) was formed as the final product of reaction at 550°. The reaction proceeds stepwise, and Tl₂V₆O₁₆ and TlVO₃ were identified as intermediates. For the molar ratio of 2∶3, impure thallium hexavanadate (Tl₂V₆O₁₆) was obtained as the final product of reaction.

     

Thallium(I)-Uranates(VI)

The solid state preparation, thermal and hydrolytic characteristics of thallium(I)—uranates(VI) are described. The phases identified were Tl₂UO₄, Tl₂U₂O₇ and a range of solid solution (Tl₂O. 2,33 UO₃? Tl₂O. 6 UO₃). The thallium uranates are isostructural with the corresponding potassium uranates. Tl₂U₂O₇ is the stable phase formed from the other uranates on hydrolytic treatment. The thallium uranates lose thallium(I) oxide on heating to temperatures above 750°C and the order of thermal stability is Tl₂U₆O₁₉～Tl₂U₃O₁₀～Tl₂U₂O₇»Tl₂UO₄.     

Thermal decomposition of ammonium metavanadate supported on Al2O3

The thermal decomposition of ammonium metavanadate supported on aluminium oxide was investigated using DTA, TG and X-ray diffraction techniques.The results obtained revealed that ammonium vanadate decomposed at 225–250°C giving an intermediate compound ((NH₄)₂V₆O₁₆) which decomposed readily at 335–360°C producing V₂O₅. Alumina was found to chance the formation of the intermediate compound and retard its decomposition. Some of the V⁵⁺ ions of V₂O₅ lattice seemed to be reduced into V⁴⁺ and V³⁺ ions by heating in air at 450°C in the presence of Al₂O₃. Such a reaction was attributed to dissolution of some Al³⁺ ions in the V₂O₅ lattice via location in interstitial positions and/or in cationic vacancies. Al₂O₃ was found to interact with V₂O₅ at 650° C giving well-crystalline A1VO₄ which decomposed at about 750°C forming well-crystalline δ-Al₂O₃ and V₂O₅,. Pure Al₂O₃, heated in air at 1000°C, existed in the form of the κ-phase which, on mixing with V₂O₅ (0.5 V₂O₅:1 Al₂O₃) and heating in air at 1000°C, was converted entirely to the well-crystalline α-Al₂O₃ phase.     

Über die Phasenbreite von V2O5 im Temperaturbereich von 450°C bis 620°C

About the Homogeneity Range of V₂O₅ in the Temperature Range of 450°C to 620°C The influence of the deposition temperature T₁ on the homogeneity range of V₂O₅-crystalls was investigated by using a solid electrolyte cell. The deviation x in V₂O_5–x from the stoichiometric composition was obtained with: x = 0.0066 at T₁ = 450°C up to x = 0.0326 at T₁ = 620°C.     

Oxydation intermetallischer Phasen: K4{Na2[Tl2O6]} aus NaTl und K2O2

Oxidation of Intermetallic Phases: K₄{Na₂[Tl₂O₆]} from NaTl and K₂O₂ The hitherto unknown K₄{Na₂[Tl₂O₆]} was prepared in form of transparent, yellow single crystals from NaTl and KO_1,08 (molar ratio 1:1.3; sealed Ag-cylinder; 450°C, 30 d). The structure determination (four-circle diffractometer, MoKα, 1 280 out of 1 523 I_o(hkl), R = 5.75%, R_w = 4.58%) confirms the space group P2₁/c with a = 641.3 pm, b = 691.1 pm, c = 1188.5 pm, β = 95.69° and Z = 2. As characteristic building units of the structure there are doubles of tetrahedra of [Tl₂O₆] and [Na₂O₆]. The compound is isotypic with Cs₆[In₂O₆] and Rb₆[Tl₂O₆]. The Madelung Part of Lattice Energy, MAPLE, the Mean Fictive Ionic Radii, MEFIR, Effective Coordination Numbers, ECoN, and Charge Distribution, CHARDI, are calculated.     

Neue Metalloxide mit Tetraeder-Doppel als Baugruppe: Rb6[Tl2O6] und Cs6[In2O6]

New Metal Oxides with Doubles of Tetrahedra as Building Units: Rb₆[Tl₂O₆] and Cs₆[In₂O₆] We prepared the hitherto unknown Rb₆[Tl₂O₆] and Cs₆[In₂O₆] by heating mixtures of Tl₂O₃ and RbO_0.60 (Rb:Tl = 3.5:1) as well as In₂O₃ and CsO_0.53 (Cs:In = 3.5:1) as single crystals [closed Ag-cylinder, 650°C, 14 d]. The single crystals of Rb₆[Tl₂O₆] are yellow, those of Cs₆[In₂O₆] pale yellow, all transparent and rude. The new type of structure was elucidated by 4-circle-diffractometer (PW 1100) data. Rb₆[Tl₂O₆]: P2₁/a; a = 1145,7(3), b = 713,3(1), c = 783,9(2) pm, β = 93,73° (2), Z = 2; Ag–Kα, 2100 out of 2531 I₀(hkl), R = 9,6% and R_w = 8,9%. Cs₆[In₂O₆]: P2₁/a; a = 1178,5(4), b = 730,7(2), c = 816,3(2) pm, β = 95,38° (3), Z = 2; Mo–Kα, 1584 out of 2032 I₀(hkl), R = 9,25%, and R_w = 8,44%. The Madelung Part of Lattice Energy, MAPLE, is calculated and discussed.     

Substrate temperature effects on the structural,compositional, and electrical properties of VO2 thin films deposited by pulsed laser deposition

The vanadium dioxide (VO₂) thin films were deposited on silicon (100) substrate using the pulsed laser deposition technique. The thin films were deposited at different substrate temperatures (500°C, 600°C, 700°C, and 800°C) while keeping all the other parameters constant. X‐ray diffraction confirmed the crystalline VO₂ (B) and VO₂ (M) phase formation at different substrate temperatures. X‐ray photoelectron spectroscopy analysis showed the presence of V⁴⁺ and V⁵⁺ charge states in all the deposited thin films which confirms that the deposited films mainly consist of VO₂ and V₂O₅. An increase in the VO₂/V₂O₅ ratio has been observed in the films deposited at higher substrate temperatures (700°C and 800°C). Scanning electron microscope micrographs revealed different surface morphologies of the thin films deposited at different substrate temperatures. The electrical properties showed the sharp semiconductor to metal transition behavior with approximately 2 orders of magnitude for the VO₂ thin film deposited at 800°C. The transition temperature for heating and cooling cycles as low as 46.2°C and 42°C, respectively, has been observed which is related to the smaller difference in the interplanar spacing between the as‐deposited thin film and the standard rutile VO₂ as well as to the lattice strain of approximately −1.2%.     

Hochdrucksynthesen von Carbonaten. VIII. Thallium-Lanthanoid-Carbonate

High Pressure Syntheses of Carbonates. VIII. Thallium Lanthanoid Carbonates The ternary carbonates TlLn(CO₃)₂ with Ln = La to Lu and Y are synthesized at 350°C by dehydration of the carbonates TlLn(CO₃)₂ · xH₂O or at 500°C by reaction of Tl₂CO₃ and Ln₂(C₂O₄)₃ · yH₂O under 3000 bar CO₂. X-ray and IR investigations show the existence of five different structures. The compound Tl₅La(CO₃)₄ is synthesized and X-ray and IR investigations were performed.     

Thallium alloys of the rare earth: Sm?TI Phase diagram and molar volumes of the rare earth thallides

The Sm? Tl system has been studied by differential thermal, metallographic and X-ray analyses. The following intermediate phases were observed: Sm₂Tl (decomposes at 1030 ± 10°C); Sm₅Tl₃ (decomposes at 1060 ± 10°C); SmTl (melting point, 1220 ± 20°C); Sm₃Tl₅ (decomposes at 940 ± 10°C); SmTl₃ (melting point, 870 ± 5°C). Three eutectics occur: β-Sm—Sm₂Tl (840 ± 10°C, 18.0 ± 0.5 at % Tl); Sm₃Tl₅—SmTl₃ (860 ± 5°C, 72.0 ± 0.5 at % Tl); SmTl₃—β-Tl (～303°C, greater than 99.5 at % Tl); there is an eutectoidal reaction at 760 ± 10°C and 10 ± 1 at % Tl (decomposition of β-Sm phase). Following crystal structures have been determined or confirmed: Sm₂Tl hexagonal hP6—Ni₂In-type, Sm₅Tl₃ tetragonal tI32—W₅Si₃-type, SmTl cubic cI2—W or cP2—CsCl-type, SmTl tetragonal tP4—AuCu I-type, Sm₃Tl₅ orthorhombic oC32—Pu₃Pd₅ like-type, SmTl₃ cubic cP4—AuCu₃-type. The characteristics of the phase diagram and the molar volumes of the Sm? Tl compounds are compared with those of other RE? Tl alloys and briefly discussed.     

Zum System V2O5?K2SO4

The phase diagram of the system V₂O₅? K₂SO₄ was established by means of X-ray diffraction and DTA. An endothermal reaction leads to the compound 5V₂O₅·3K₂SO₄ which melts at 510°C, crystallizes needle-shaped and forms hydrates. Eutectics occur at 31 (505°) and 55 mole-% K₂SO₄ (455°C).     

Phase equilibria in the CuBr−TlBr system

The phase diagram for the CuBr?TlBr system was investigated using the differential thermal analysis completed by the X-ray powder diffraction data. Three intermediate phases were found: Tl₂CuBr₃ (stable from room temperature up to 234°C where decomposes in the solid state), Tl₃Cu₂Br₅ (stable between 168°C and its incongruent melting point 262°C) and a nonstochiometric δ phase (centered about 75 mol% CuBr and stable above about 240°C).     

V<Subscript>3</Subscript>O<Subscript>7</Subscript> · H<Subscript>2</Subscript>O oxide nanostructures: Synthesis and study

Nanorods of orthorhombic V₃O₇ · H₂O with the parameters a = 16.805 Å, b = 9.428 Å, and c = 3.660 Å are prepared under hydrothermal conditions (T = 180–190°C, τ = 30–40 h) from the V₂O₅ · nH₂O/H₂C₂O₄ · 2H₂O composite. The particle diameter is 40–70 nm, and the length is several micrometers. The IR spectra, electric conductivity, and thermal properties of the nanorod powder are studied. In air V₃O₇ · H₂O begins to decompose at temperatures above 150°C, and at 350°C nanobelts V₂O₅ 40–100 nm wide and 40 µm long are formed. A mechanism of nanostructure formation is suggested.     

Ein neues Syntheseverfahren für Vanadiumbronzen. Die Kristallstruktur von β?Ag0,33V2O5. Verfeinerung der Kristallstruktur von ϵ?Cu0,76V2O5

A Novel Means of Synthesis for Vanadium Bronzes. Crystal Structure of β? Ag_0.33V₂O₅. Refinement of the Crystal Structure of ?? Cu_0.76V₂O₅ Ag_0.33V₂O₅ and Cu_0.76V₂O₅ were obtained by heating equimolar mixtures of AgI + V₂O₅ (700°C) and CuI + V₂O₅ (525°C), respectively, in sealed quartz glass ampoules. In each case, one of the well-formed crystals served for an X-ray structure analysis. Ag_0.33V₂O₅ has the structure known of the β phase of the vanadium bronzes, i. e. layers of edge-sharing, distorted VO₆ octahedra are liked by certain common octahedron vertices, the Ag atoms randomly occupy two positions with occupation probabilities of 0.5. Cu_0.76V₂O₅ has the previously determined structure of the ? phase, however, its space group is not Cm but C2/m.     

Crystal structure of catena-(2-thiobarbiturato) dithallium(I)

By powder X-ray diffraction the crystal structure of catena-(2-thiobarbiturato)dithallium(I) C₄H₂N₂O₂STl₂ (C₄H₄N₂O₂S is 2-thiobarbituric acid, H₂TBA), Tl₂TBA, is determined. Crystallographic data for Tl₂TBA are as follows: a = 15.1039(3) Å, b = 12.0818(2) Å, c = 3.86455(6) Å, β = 97.203(1)°, V = 741.34(2) ų, space group P2₁/n, Z = 4. There are two non-equivalent thallium atoms in the structure. The Tl1 polyhedron is a distorted trigonal prism due to the shortened Tl-S contact (3.634 Å), and the Tl2 polyhedron is a distorted square antiprism.     

Crystal structure of thallium(I) 2-thiobarbiturate

The crystal and molecular structures of thallium(I) thiobarbiturate C₄H₃N₂O₂STl (C₄H₄N₂O₂S is 2-thiobarbituric acid, Н₂ТВА) have been determined. Crystallographic data for Tl(НТВА) are a = 11.2414(7) Å, b = 3.8444(3) Å, с = 14.8381(9) Å, β = 99.452(2)°, V = 649.00(7) ų, space group P2/с, Z = 4. Each of the two independent thallium ions is bonded to four oxygen and two sulfur atoms to form a distorted tetrahedron. N?H…O and C?H…S hydrogen bonds form a branched three-dimensional network. The structure is also stabilized by π?π interaction between heterocyclic НТВА^- ions. The IR spectra of Tl(НТВА) agree with X-ray powder diffraction data. The compound is also stable below 280°C, and Tl₂SO₄ is one of the thermolysis products in an oxidative medium in the region of 500?650°C.     

Preparation and studies of a new ammonium vanadium bronze, (NH4)xV2O5

A new bronze-type phase of composition (NH₄)_0.40±0.02V₂O₅ is obtained around 230°C during the thermal decomposition of NH₄VO₃ in hydrogen atmosphere. The bronze intermediate is characterized by X-ray diffraction, electrical conductivity, magnetic susceptibility, and ESR studies. It is found to be isostructural with other known β-type vanadium bronzes of general formula M_xV₂O₅, where M is usually a monovalent metal. Electrical conductivity and magnetic studies indicate the localized character of conduction electrons at V⁺⁴ sites. At high temperatures (>400°C), the bronze undergoes decomposition and subsequent reduction to V₂O₃ in hydrogen atmosphere.     

Effect of γ-irradiation and doping with MoO3 and V2O5 on surface and catalytic properties of manganese oxides

The effects of γ-irradiation (0.2–1.6 MGy), thermal treatment and doping with MoO₃ and V₂O₅ (0.25–4 mol%) on the surface and catalytic properties of manganese oxides prepared by thermal decomposition of manganese carbonate at 400°C and 600°C have been investigated. The techniques employed were X-ray diffraction, nitrogen adsorption at −196°C, oxidation of CO by O₂ at 120–220°C and decomposition of H₂O₂ at 20–50°C. The results revealed that γ-irradiation decreased the particle size of manganese oxides, increased their specific surface areas, decreased the amount of surface excess oxygen and decreased their catalytic activities. The doping with MoO₃ and V₂O₅ conducted at 600°C brought about a measurable decrease in the BET-surface area and catalytic activities of the treated solids. These results were discussed in terms of splitting of manganese oxide particles and removal of chemisorbed oxygen by treating with γ-irradiation and formation of manganese molybdate and vanadates by treating with the used dopant oxides.     

Zur Bedeutung von V2O3(OH)4(g) für den chemischen Transport von V2O5(s) in Anwesenheit von Wasser. Nachweis des Gasteilchens,thermodynamische Daten und Modellrechnungen

V₂O₃(OH)₄(g), Proof of Existence, Thermochemical Characterization, and Chemical Vapor Transport Calculations for V₂O₅(s) in the Presence of Water By use of the Knudsen-cell mass spectrometry the existence of V₂O₃(OH)₄(g) is shown. For the molecules V₂O₃(OH)₄(g), V₄O₁₀(g), and V₄O₈(g) thermodynamic properties were calculated by known Literatur data. The influence of V₂O₃(OH)₄(g) for chemical vapor transport reactions of V₂O₅(s) with water ist discussed. Δ_BH°(V₂O₃(OH)₄(g), 298) = –1920 kJ · mol^–1 and S°(V₂O₃(OH)₄(g), 298) = 557 J · K^–1 · mol^–1, Δ_BH°(V₄O₁₀(g), 298) = –2865,6 kJ · mol^–1 and S°(V₄O₁₀(g), 298) = 323.7 J · K^–1 · mol^–1, Δ_BH°(V₄O₈(g), 298) = –2465 kJ · mol^–1 and S°(V₄O₈(g), 298) = 360 J · K^–1 · mol^–1.     

Paramagnetic resonance absorption in reduced tellurium?vanadium oxides

Hydrogen reduction of Te₂V₂O₉ at temperatures ranging from 300 to 450°C was studied by means of x-ray diffraction as well as ESR and IR spectroscopies. The reduction sets in through the formation of oxygen vacancies in Te₂V₂O₉ giving several types of transient VO²⁺ species. Subsequently, TeVO_4·17 and β-TeVO₄ (the latter only in minor amounts) are detected, in accordance with the phase diagram of the V₂O₅? TeO₂? VO₂ ternary system. The reduction stages leading to TeVO_4·17 and β-TeVO₄ are slow until 350°C, whereas rapid decomposition of the binary oxides (to give V₂O₃) is observed at higher temperatures. The magnetic interactions between paramagnetic V⁴⁺ ions in the reaction products are related to the structure of the reduced oxides.     

Raman spectroscopic characterization of the microstructure of V2O5 films

The vanadium pentoxide (V₂O₅) films were deposited on silicon wafer by DC magnetron sputtering. By Raman scattering measurements, the microstructure properties of the V₂O₅ films prepared with different O₂–Ar gas flow ratios and annealed at different temperatures were studied, respectively. The results revealed that the increase of O₂–Ar gas flow ratio during sputtering was of advantage to prepare the V₂O₅ film with desired layer structure. A high post-annealing temperature (below 500 °C) induced the crystallization and the formation of the integrated structure of V₂O₅ film. However, it was found that both intensities of Raman scattering peaks at 146 cm^?1 and 994 cm^?1, respectively, decreased for samples annealed at a temperature of 550 °C. The peak at 146 cm^?1 was attributed to skeleton bent vibration and that at 994 cm^?1 was due to the stretching vibration of vanadyl V=O_A bond. It showed that the high-temperature annealing was believed to have distorted the microstructure of V₂O₅ films. The oxygen vacancies were, therefore, induced, which benefited the formation of V-O_A-V bonds between layers. The result of X-ray diffraction measurements was in good agreement with that of Raman scattering spectra.