Heat capacity measurement of cubic lithium tungsten bronzes from 200 to 800°K

Heat capacities of three cubic lithium tungsten bronze samples (Li_xWO₃) with x values of 0.363, 0.437, and 0.478 were measured from 200 to 800°K. Heat capacities per gram-atom at the same temperature of Li_0.363WO₃ and Li_0.437WO₃ were equal within experimental error and also equal to those of Na_0.485WO₃, Na_0.698WO₃, and Na_0.794WO₃, regardless of the difference of the composition. λ-type heat capacity anomalies were observed around 330, 460, and 590°K in Li_0.363WO₃ and around 330 and 460°K in Li_0.437WO₃ and Li_0.478WO₃, showing the existence of second-order phase transitions. The entropy increments of the transitions were obtained as 1.36, 0.45, and 1.68 J mole^?1 K^?1 for Li_0.363WO₃, 1.09 and 0.59 J mole^?1 K^?1 for Li_0.437WO₃, and 1.42 and 0.50 J mole^?1 K^?1 for Li_0.478WO₃.     

Na0.33WO3溶胶及薄膜的制备与光致变色性质研究

无机光致变色材料在图像显示、光记录、信息存储和光转换方面有着巨大的潜在应用前景,引起了材料工作者的广泛重视[1￣3]。氧化钨是一种重要的无机光致变色材料,目前对氧化钨的研究多以无定     

Tungsten oxide bronzes with alkali metals

Single-phase samples of tungsten bronzes M _x WO₃ (M = K⁺, Rb⁺, Cs⁺) are prepared by solid-state synthesis. The reversibility of the M_0.33WO₃/M⁺-solid electrolyte interface is studied subject to the alkali metal nature and humidity over a wide temperature interval. The exchange current density at 24°C and 58%-relative humidity is 3.6 × 10^?4 A/cm² for the Rb_0.33WO₃/Rb⁺-solid electrolyte interface; 2.2 × 10^?4 A/cm² for the Cs_0.33WO₃/Cs⁺-solid electrolyte interface; and 1.3 × 10^?4 A/cm² for the K_0.33WO₃/K⁺-solid electrolyte interface. A correlation between the reversibility of the bronze|solid electrolyte interface, which is characterized by the exchange current density, and the rate of potential equilibration in sensor systems, where the bronze is a reference electrode, is revealed. Ionic component of the conductivity of the synthesized tungsten oxide bronzes is measured at a background of the predominant electronic conductivity. The ionic conductivity is three orders of magnitude lower than the electronic conductivity; it decreases in the series Rb_0.33WO₃ > Cs_0.33WO₃ > K_0.33WO₃, amounting to 2.3 × 10^?2, 2.1 × 10^?3, and 2 × 10^?4 S cm^?1, respectively. The working capacity of the M_0.3WO₃ bronzes as reference electrodes in sensor systems for carbon dioxide detection is evaluated. The plots of the cell potential vs. the CO₂ concentration in the electrochemical cells are linear, their slopes (59 ± 1 mV/decade) are characteristic for one-electron process. The fastest response to changes in the CO₂ concentration was obtained with the sensor system that used Rb_0.33WO₃ as reference electrode.     

Darstellung und Struktur von Li5Ga4

Preparation and Crystal Structure of Li₅Ga₄ Li₅Ga₄ has been established as further, hitherto unknown phase in the LiGa system. The new compound crystallizes in the trigonal system (P3 m1—D_3d³) with a = 437.5 ± 0.2 pm, c = 825.7 ± 0.2 pm, c/a = 1.885. The structure is strongly related to those of LiGa and Li₃Ga₂.     

Über quaternäre Oxowolframate (VI) Na6Li2[W2O10] - ein Diwolframat

On Quaternary Oxotungstates (VI). Na₆Li₂[W₂O₁₀] — a Ditungstate For the first time, Na₆Li₂[W₂O₁₀] has been prepared by annealing mixtures of WO₃, Na₂O and Li₂O with W:Na:Li = 1:3:1 [closed Pt-tube in quartz-glass ampoule, 840°C, 60 d (single crystals)]. The colourless crystals are of squatted shape. The structure determination [1813/I₀(h kl), four-cycle diffractometer PW 1100 (Fa. Philips), ω-scan, AgK_α, R = 8.32%, absorption not considered] confirms the space group P1 with a = 784.66(11), b = 602.53(7) c, = 563.81(11) pm α = 106.784(14)°, β = 114.548(14)°, γ = 91.082(13)°, Z = 2, d_x = 4.92 g · cm^?3, d^pyk = 4.85 g · cm^?3. The structure may be described as a distorted derivative of the NaCl-type. The Madelung Part of Lattice Energy, MAPLE, Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, are calculated and discussed.     

Thermochemistry of hydrogen tungsten bronze phases HxWO3

The enthalpies of formation of two hydrogen tungsten bronze phases H_0.35WO₃ and H_0.18WO₃ have been determined by solution calorimetry. Values obtained for formation from H₂(g) and WO₃(s) at 298.15 K were H_0.35WO₃(s), ?9.6 ± 0.8 kJ mole^?1 and H_0.18WO₃(s), ?4.8 ± 0.6 kJ mole^?1. The stabilities of these phases towards decomposition, disproportionation and oxidation are discussed.     

Synthesis and in-situ noble metal modification of WO3·0.33H2O nanorods from a tungsten-containing mineral for enhancing NH3 sensing performance

Ag- and Pt-doped WO₃·0.33H₂O nanorods with high response and selectivity to NH₃ were synthesized from a tungsten-containing mineral of scheelite concentrate by a simple combined process, namely by a high pressure leaching method to obtain tungstate ions-containing leaching solution and followed by a hydrothermal method to prepare corresponding nanorods. The microstructure and NH₃ sensing performance of the final products were investigated systematically. The microstructure characterization showed that the as-prepared WO₃·0.33H₂O nanorods had a hexagonal crystal structure, and Ag and Pt nanoparticles were uniformly distributed in the WO₃·0.33H₂O nanorods. Gas sensing measurements indicated that Ag and Pt nanoparticles not only could obviously enhance NH₃ sensing properties in terms of response, selectivity as well as response/recovery time, but also could reduce the optimal operating temperature at which the highest response was achieved. The highest responses of 22.4 and 47.6 for Ag- and Pt-doped WO₃·0.33H₂O nanorods to 1000 ppm NH₃ were obtained at 225 and 175 °C, respectively, which were about four and eight folds higher than that of pure one at 250 °C. The superior NH₃ sensing properties are mainly ascribed to the catalytic activities of noble metals and the different work functions between noble metals and WO₃·0.33H₂O.     

Phase behavior of Li2WO4 at high pressures and temperatures

The phase diagram of Li₂WO₄, previously studied by Yamaoka et al. (J. Solid State Chem.6, 280 (1973)) has been revised. Li₂WO₄ II is stable at atmospheric pressure below ～310°C. This phase appears to be a modified spinel, and is tetragonal, a, c = 11.941, 8.409Å, Z = 16, space group $\text{I4}{}_1\text{amd}$. The melting curve of phenacite-type Li₂WO₄ I rises with pressure with a slope of 0.9°C/kbar to the III/I/liquid triple point at 3.1 kbar, 743°C, beyond which the melting curve of orthorhombic Li₂WO₄ III rises steeply with pressure (initial slope 31°C/kbar). The Li₂WO₄$\text{I}\text{III}$ transition line at 3 kbar is almost independent of temperature, i.e., the $\text{I}\text{III}$ transition entropy is zero. Li₂WO₄ II is 21.3% denser than Li₂WO₄ I at ambient conditions.     

Phase transformations in Li2WO4 at high pressure

The phase diagram of Li₂WO₄ has been determined at high pressure up to 160 kbars and a temperature of 800°C. Three new high-pressure phases have been found in the present study. Crystallographic data are given for Li₂WO₄ III and Li₂WO₄ IV by means of single crystal and powder X-ray analyses. Li₂WO₄ III is orthorhombic with the large unit cell containing 16 molecules and having the edges: a₀ = 10.12(4) Å, b₀ = 10.07(1) Å, c₀ = 11.68(6) Å. Li₂WO₄ IV has an orthorhombic unit cell with the parameters: a₀ = 4.96(7) Å, b₀ = 9.72(8) Å, c₀ = 5.93(8)Å and Z = 4. The total volume decrease is estimated to be 24.8% through the high pressure transformations in Li₂WO₄. No spinel-like structure could be found in the present study.     

Electrochemical processes of H<Subscript>2</Subscript>S detection in air and solution

An electrochemical cell of potentiometric type Na_0.5WO₃ (reference electrode)/Na⁺-solid electrolyte/PbS (working electrode) capable of rapid and selective changing of the electromotive force value owing to H₂S concentration variations in gas surroundings has been investigated at 295±1 K and a relative humidity of 52%. The sensitivity of this cell was 130 mV/decade at a H₂S concentration within the range 13–130 ppm. Sodium-conducting solid electrolytes of Na₃Zr₂Si₂PO₁₂ and Na₅GdSi₄O₁₂ compositions were used as the Na⁺ solid electrolyte. Such a cell can be used for analysis of H₂S containing water solutions when the reference electrode and the Na⁺ solid electrolyte are thoroughly isolated from the surroundings. Electronic Publication     

Interaction of salts in ionic melts of the ternary reciprocal systems Na,K‖BO2,MoO4 and Na,K‖BO2,WO4

The phase diagrams of the ternary reciprocal systems Na,K‖BO₂,MoO₄ and Na,K‖BO₂,WO₄ were studied for the first time by a calculation-experimental method and differential thermal analysis. The coordinates were determined for binary eutectics of the diagonal stable sections NaBO₂-K₂MoO₄(K₂WO₄) and the ternary invariant points e(55 mol % NaBO₂, 45 mol % K₂MoO₄, 740°C), e(55 mol % NaBO₂, 45 mol % K₂WO₄, 730°C), E(4.5 mol % NaBO₂, 78 mol % Na₂MoO₄, 17.5 mol % K₂MoO₄, 652°C), E(4.5 mol % NaBO₂, 78 mol % Na₂WO₄, 17.5 mol % K₂WO₄, 643°C), P₂(5 mol % NaBO₂, 56 mol % Na₂MoO₄, 39 mol % K₂MoO₄, 673°C), P₂(5 mol % NaBO₂, 56 mol % Na₂WO₄, 39 mol % K₂WO₄, 671°C). Binary solid solutions based on sodium and potassium metaborates were shown to be stable. Analytical models of phase equilibrium states of the ternary reciprocal systems Na,K‖BO₂,MoO₄(WO₄) were obtained, which enable one to calculate melting (crystallization) points and construct isotherms at any given composition. The specific heats of melting of samples of invariant compositions were found by quantitative differential thermal analysis.     

Über nichtstöchiometrische Wolfram-Verbindungen Synthese und Gitterkonstanten von Verbindungen der Mischkristallreihe WO3?NaWO3

On Nonstoichiometric Tungsten Compounds. Synthesis and Lattice Constants of WO₃? NaWO₃ Mixed Crystal Compounds In the range of temperature from 850 to 1300°C sodium tungsten bronzes with the formula Na_xWO₃ were prepared from a stoichiometric mixture of W, WO₃ and Na₂WO₄. The variation of lattice constant with nominal bronze composition was determined.     

Li＋, Na＋//SO42－, CO32－-H2O交互四元体系288 K介稳相平衡研究

采用等温蒸发法研究了四元体系Li^＋, Na^＋// SO₄^2－, CO₃^2－-H₂O 288 K介稳相平衡及平衡液相的密度、电导率、折光率、粘度和pH值, 测定了该四元体系288 K条件下介稳平衡溶液溶解度及物化性质. 根据实验数据绘制了相应的介稳相图. 研究发现: 该体系介稳平衡中有复盐Na₃Li(SO₄)₂•6H₂O形成. 其介稳相图中有3个共饱点, 7条单变量曲线, 平衡固相为: Li₂SO₄•H₂O, Na₂SO₄, Na₃Li(SO₄)₂•6H₂O, Li₂CO₃, Na₂CO₃•10H₂O. 复盐Na₃Li(SO₄)₂•6H₂O和一水硫酸锂(Li₂SO₄•H₂O)的结晶区较小, 而Li₂CO₃的结晶区最大; 该四元体系介稳平衡条件下未发现Na₂SO₄•10H₂O的结晶区.     

Bonding and singlet–triplet gap of silicon trimer: Effects of protonation and attachment of alkali metal cations

We revisit the singlet–triplet energy gap (ΔE_ST) of silicon trimer and evaluate the gaps of its derivatives by attachment of a cation (H⁺, Li⁺, Na⁺, and K⁺) using the wavefunction‐based methods including the composite G4, coupled‐cluster theory CCSD(T)/CBS, CCSDT and CCSDTQ, and CASSCF/CASPT2 (for Si₃) computations. Both ¹A₁ and ³ states of Si₃ are determined to be degenerate. An intersystem crossing between both states appears to be possible at a point having an apex bond angle of around α = 68 ± 2° which is 16 ± 4 kJ/mol above the ground state. The proton, Li⁺ and Na⁺ cations tend to favor the low‐spin state, whereas the K⁺ cation favors the high‐spin state. However, they do not modify significantly the ΔE_ST. The proton affinity of silicon trimer is determined as PA(Si₃) = 830 ± 4 kJ/mol at 298 K. The metal cation affinities are also predicted to be LiCA(Si₃) = 108 ± 8 kJ/mol, NaCA(Si₃) = 79 ± 8 kJ/mol and KCA(Si₃) = 44 ± 8 kJ/mol. The chemical bonding is probed using the electron localization function, and ring current analyses show that the singlet three‐membered ring Si₃ is, at most, nonaromatic. Attachment of the proton and Li⁺ cation renders it anti‐aromatic. © 2015 Wiley Periodicals, Inc.     

Complex Phosphates in the Li(Na)3]PO4-InPO4 Systems

Subsolidus sections in the systems Li₃PO₄-InPO₄ (950°C) and Na₃PO₄-InPO₄ (800, 900, and 1000°C) have been studied by X-ray powder diffraction. The compound Li₃In(PO₄)₂ has been synthesized, and the nasicon-type solid solution Li_{3(1 ? x)}In_{2 + x}(PO₄)₃ (0.67 ≤ x ≤ 0.80). has been found to exist. In the system Na₃PO₄-InPO₄, the solid solution Na_{3(1 ? x)}In_x/3PO₄ (0 ≤ x ≤ 0.2) and two complex phosphates exist: Na₃In(PO₄)₂ and Na₃In₂(PO₄)₃. These complex phosphates are dimorphic, with the irreversible-transition temperature equal to 675 and 820°C, respectively. Na₃In(PO₄)₂ degrades at 920°C. Ionic conductivity has been measured in some phases in the system.     

Neue Oxoferrate(III). Na2Li3[FeO4] und K2Li3[FeO4]

New Oxoferrates (III). Na₂Li₃[FeO₄] and K₂Li₃[FeO₄] . Na₂Li₃[FeO₄] and K₂Li₃[FeO₄] (transparent, pink or light yellow single crystals) have been prepared by heating mixtures of the oxides (Na:Li:Fe = 2.2:3.3:1; Ag-tube, 720°C, 27 d or K:Li:Fe = 2.2:3.3:1; analogous, 700°C, 40 d). Na₂Li₃[FeO₄] is isotypic with Na₂Li₃[GaO₄] (a = 832.2(1), b = 796.0(1), c = 656.3(1)pm, Pnnm) and K₂Li₃[FeO₄] with K₂Li₃[GaO₄] (a = 557.7(1), b = 880.6(1), c = 1101.8(2)pm, β = 111.51(2)°, P2₁/c). Four cycle diffractometer data: MoK_α, 525 out of 686 I₀(hkl), R = 9.36%, R_w = 5.97% or 1424 out of 1424 I₀(hkl), R = 8.45%, R_w = 5.66%. Parameters see text. The structures are characterized by calculations of the Madelung Part of Lattice Energy, MAPLE. The Effective Coordination Numbers, ECoN, which are calculated by means of Mean Fictive Ionic Radii, MEFIR, are compared with the analogous gallates.     

Phase relations,dopant effects,structure, and high electrical conductivity in the Na2WO4Na2MoO4 system

The x, T-phase diagram of the binary system Na₂WO₄Na₂MoO₄ has been redetermined at ambient pressure, taking into account the influence of hysteresis effects. Thermodynamic calculations, based upon transition entropies as determined by precision DSC (differential scanning calorimetry), indicate that the system is almost ideal with respect to the high-temperature phases.As anion dopes, Na₂SO₄ and Na₂CrO₄ give a metastable extension of the β-phase of Na₂WO₄ at decreasing temperature, involving some 40°C at 0.01 mole fraction of dopant. Cation dopes like Li₂WO₄ and K₂WO₄ behave quite differently.The electrical conductivity through the phase diagram is high in the α-phase (σ ～ 10^?2 mho cm^?1) almost regardless of composition. The anomalous high conductivity of the β-phase decreases with increasing molybdate content. In pure Na₂MoO₄ an anomaly occurs at the α-α₂ transition, resembling the behavior of Na₂WO₄ at the β-α transition. The (highest) α₂-phase is hexagonal, ($\text{P6}{}_3\text{mmc}$, showing large anisotropic thermal vibrations. The α-phase is orthorhombic (Fddd) as is the β-phase (probably Pbn2₁).     

The preparation,phase relationships,and Eu-151 Mössbauer spectroscopy of europium tungsten bronzes and related phases

Crystal chemistry and phase relations for the bronze-forming region of the EuWO system have been investigated. A bronze Eu_xWO₃ is stable up to 1000°C when x ? 0.125 and in the region 0.085 ? x ? 0.125 the symmetry is cubic. A tetragonal bronze exists at x = 0.05, and an orthorhombic bronze with a structure closely related to the orthorhombic form of WO₃ exists below x = 0.01. Mössbauer spectra at room temperature and at 80 K indicate that in all these phases the europium is highly ionized as Eu(III) with no electron localization to give (EuII) even at low values for x. The decomposition products of the bronzes have been established, and the Mössbauer parameters for the highly nonstoichiometric tungstates Eu_xWO₄ were determined. Both Eu(II) and Eu(III) resonances were obtained, and a cation vacancy model for Eu_xWO₄ was found to fit the data best. In conformity with the foregoing data, a sample of composition “Eu₂W₂O₇” was found not be be a pyrochlore but to comprise a mixture of Eu₆WO₁₂, Eu_xWO₄, and W. The phase relationships for the europium bronze system Eu_xWO₃ are compared with those of other ionic bronzes Na_xWO₃, Li_xWO₃, and Al_xWO₃.     

Hexagonal tungsten bronze-type FeIII fluoride: (H2O)0.33FeF3; crystal structure,magnetic properties,dehydration to a new form of iron trifluoride

(H₂O)_0.33FeF₃, grown by hydrothermal synthesis, crystallizes in the orthorhombic system with cell dimensions a = 7.423(3) Å, b = 12.730(4) Å, c = 7.526(3)Å, and space group Cmcm, Z = 12. The structure, derived from single crystal X-ray diffraction data (605 independent reflections) is refined to R = 0.019 (R_ω = 0.021). The framework of the Fe^IIIF₆ octahedra is related to that of hexagonal tungsten bronze (HTB) Rb_0.29WO₃. At 122°C, zeolithic water is evolved from hexagonal tunnels without any noticeable change of the fluorine skeleton. The related anhydrous compound represents a new form of iron trifluoride which is denoted HTBFeF₃; at 525°C, it transforms into the cubic form of ReO₃-type. (H₂O)_0.33FeF₃ and HTBFeF₃ are antiferromagnetic, with Néel temperatures of T_N = 128°7 ± 0.5 K and T_N = 97 ± 2 K, respectively.     

Calorimetric study of high-pressure polymorphs of Li2WO4 and Li2MoO4

Heats of transition among the Li₂WO₄ polymorphs, Li₂WO₄I (phenacite-type structure), Li₂WO₄II, Li₂ WO₄III, and Li₂WO₄IV, and that between Li₂MoO₄ (phenacite) and Li₂MoO₄(spinel) were measured by transposed temperature drop calorimetry. The heats of fusion of Li₂WO₄I and Li₂MoO₄(ph) were also obtained. Using these data, the phase boundaries among the polymorphs of Li₂WO₄ and of Li₂MoO₄ were calculated. The calculated phase diagrams were compared with those reported previously. They agree well for Li₂WO₄ but show significant discrepancies, perhaps related to problems in attaining equilibrium at lower temperature, for Li₂MoO₄.