Effect of Ho substitution on the ionic conductivity of La2Mo1.7W0.3O9 oxygen ion conductor

Partial substitutions of Ho at the La-site of La₂Mo_1.7W_0.3O_9−δ were carried out. Compound La_2−xHo_xMo_1.7W_0.3O_9−δ (x = 0, 0.05, 0.1, 0.15, 0.2, 0.3, 0.5) has been synthesized by solid state reaction technique. The specimens were characterized by XRD, SEM, DSC for crystal structure, surface morphology, phase transition and ac impedance spectroscopy for conductivity and other electrical parameter determination. Partial substitution of Ho at the La-site of La₂Mo_1.7W_0.3O_9−δ, increases the conductivity within the substitutional range, x ≤ 0.2. The phase transition of La₂Mo₂O₉ is suppressed in doped compound and a transition from Arrhenius to VTF behavior of temperature dependence of conductivity is observed around 500 °C. The conductivity is found to be high in the intermediate temperature region and at high temperature the conductivity of La_2−xHo_xMo_1.7W_0.3O_9−δ (0.05 ≤ x ≤ 0.2) is almost similar with that of La₂Mo₂O₉. The decrease in energy barrier enhances the thermally assisted process to start at lower temperature.     

Thermodynamic stability, structural and electrical characterization of mixed ionic and electronic conductor La2Mo2O(8.96)

Thermogravimetric analysis (TGA) technique in controlled oxygen partial pressure (pO(2)) atmospheres has been used to obtain equilibrium oxygen content data as a function of pO(2) on the La(2)Mo(2)O(9-δ) system resulting from the partial reduction of fast oxide-ion conductor La(2)Mo(2)O(9) (LM). Thermodynamic conditions for stabilization of crystalline La(7)Mo(7)O(30) and amorphous La(2)Mo(2)O(7-y) at 718 °C have been determined and discussed. At 608 °C, the compound reported for the first time La(2)Mo(2)O(8.96) (LM896) has been found. The crystalline form and transition temperature in LM896 have been identified by X-ray diffraction at room temperature (XRD) and at controlled temperature. Conductivity curves obtained by electrochemical impedance spectroscopy (EIS) as a function of temperature for both LM and LM896 have been compared. The results indicate that LM896 is a mixed ionic and electronic conductor (MIEC).     

La1.95Sr0.05Mo2O9固体电解质的电性质

采用溶胶-凝胶法合成了La1.95Sr0.05Mo2O9固体电解质材料,采用SEM,XRD,交流阻抗谱、气体浓差电池、氧泵等方法对样品进行了表征.结果表明,制得的样品为立方结构;在600～1000℃下氧浓差电池电动势的实测值与理论值吻合得很好,氧离子迁移数为1,表明该陶瓷样品在该温度下氧气气氛中为一纯氧离子导体;离子电导率随温度升高而增大,1000 ℃时达到最大值0.12 S·cm-1.高于相同条件下母体的电导率(0.03 S·cm-1).     

Topological metastability and oxide ionic conduction in La(2)-(x)Eu(x)Mo(2)O(9)

The effect of partial substitution, up to x = 0.4, of La by trivalent Eu on the phase stability, thermal expansion, and transport properties of La2Mo2O9 are investigated using temperature-controlled X-ray powder diffraction, differential thermal analysis, and complex impedance spectroscopy. At low europium content (x < or = 0.1), the alpha-beta phase transition is observed at a temperature dependent on the sample shaping (powder, pellet, etc.). At high europium content (x > or = 0.25), the samples remain cubic (beta phase), regardless of the shaping. In the intermediate range of europium content (x = 0.15, 0.2), the phase stability is highly sensitive to the thermal history and the sample shaping, with a double-reversed beta-alpha-beta transition suppressed by the shaping/sintering process. The influence of the amount of europium on the transport mechanisms and parameters is studied in both low- (Arrhenius) and high-temperature (Vogel-Tammann-Fulcher = VTF) regimes. If the effect of substitution is rather mild and monotonous within each transport regime and crystallographic phase, an abrupt change in the Arrhenius parameters between the alpha- and beta-type phases is observed.     

新型固体电解质La2Mo2O9的制备及其性能

用固相法制备了新型固体电解质La2Mo2O9, 用热膨胀仪、 X射线衍射仪和Raman光谱分析了La2Mo2O9相的形成过程. 用交流阻抗谱和热膨胀仪对合成样品的电学和热学性能进行了研究, 分析了热处理温度对La2Mo2O9相的形成过程和电学性能的影响, 确定了样品获得高电学性能的最佳条件. 研究结果表明: 600 ℃时样品中开始形成La2Mo2O9相, 700 ℃以上烧结的样品可获得具有完整氧空位的La2Mo2O9相. 900 ℃烧结10 h可获得具有高密度和高电导率的La2Mo2O9氧离子导体. 样品的电学性能随烧结温度的升高而增大, 900 ℃时烧结的样品在800 ℃时的电导率为0.067 S·cm-1, 远高于同温度下YSZ的电导率, 与晶粒电阻相比, 晶界电阻非常小. 用热膨胀仪测得La2Mo2O9在555 ℃时有一个一级相变, 对应α-La2Mo2O9到β-La2Mo2O9的相变.     

Synthesis of New Solid Solutions on Neodymium-stabilized La2Mo2O9

Oxide ion conductors form a class of materials which are widely sought for and studied since they can be used in different field among solid oxide fuel cells (FOFC), oxygen sensors, oxygen pumping devices, or oxygen-permeable membrane catalysts, for instance1-3. Now research focuses on the oxide ion conductors with new structure and improving the conductivity or lowering the operating temperature. Recently P.Lacorre et al.4 have reported a novel oxide-ion conductor based on La2Mo2O9. F.…     

95Mo and 17O NMR studies of aqueous molybdate solutions

Aqueous molybdate solutions with molybdenum concentrations of [Mo]=1, 0.4, and 0.2 M have been studied by NMR at pH 7-1 and in 0.3-6 M HClO4. The 95Mo NMR spectrum of isopolyanion (IPA) Mo7O24(6-) (I) at pH=5 consists of a signal at 210 ppm and two overlapping peaks at 32 and approximately 15 ppm with the intensity ratio approximately 1:4:2, and that of beta-Mo8O26(4-) (II) consists of two signals at approximately 100 and 10 ppm with the intensity ratio approximately 1:3. A broad 95Mo NMR line at around 0 ppm was observed in the pH range of IPA Mo36O112(8-) (III), and a signal of cationic oxospecies including MoO2(2+) (IV) was observed from -62 to -69 ppm. Two protonation sites of IPA I have been identified from 17O NMR spectra, which suggests binding of up to two protons. The distribution diagram, derived from the 95Mo NMR spectra, is given for [Mo]=0.4 M. The 95Mo NMR signals shift to lower frequencies with increasing number and strength of the Mo-O terminal bonds.     

Lithium assisted electrochemical reduction of uranium oxide in room temperature ionic liquid

Lithium assisted electrochemical reduction of U₃O₈ in the room temperature ionic liquid (RTIL), N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide (MPPiNTf₂), was studied to explore the feasibility of using RTILs for direct electrochemical reduction of uranium oxide at near ambient temperature. The electrochemical behavior of Li⁺ in MPPiNTf₂ at stainless steel electrode was investigated by cyclic voltammetry and chronoamperometry. The cyclic voltammogram of LiNTf₂ in MPPiNTf₂ at 373 K consisted of a surge in cathodic current occurring at a potential of −2.8 V (vs. Fc/Fc⁺) due to the reduction of Li(I) to metallic form. The nucleation phenomenon observed in the voltammogram was investigated by chronoamperometry. Electrodeposition of metallic lithium on U₃O₈ particles contained in a stainless steel (SS) basket was carried out to examine the feasibility of reducing U₃O₈ to metallic form. The results are discussed in this paper.     

Shear-induced lamellar phase of an ionic liquid crystal at room temperature

The phase behaviour of a number of N-alkylimidazolium salts was studied using polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. Two of these compounds exhibit lamellar mesophases at temperatures above 50°C. In these systems, the liquid crystalline behaviour may be induced at room temperature by shear. Sheared films of these materials, observed between crossed polarisers, have a morphology that is typical of (wet) liquid foams: they partition into dark domains separated by brighter (birefringent) walls, which are approximately arcs of circle and meet at “Plateau borders” with three or more sides. Where walls meet three at a time, they do so at approximately 120° angles. These patterns coarsen with time and both T1 and T2 processes have been observed, as in foams. The time evolution of domains is also consistent with von Neumann's law. We conjecture that the bright walls are regions of high concentration of defects produced by shear, and that the system is dominated by the interfacial tension between these walls and the uniform domains. The control of self-organised monodomains, as observed in these systems, is expected to play an important role in potential applications.     

Zur Kenntnis von Cu6La4Mo9O36

About Cu₆La₄Mo₉O₃₆ Single crystals of Cu₆La₄Mo₉O₃₆ were prepared and investigated by X-ray work. It shows trigonal symmetry, space group R3c — C; a = 20.892, c = 12.754 Å; Z = 6. Cu₆La₄Mo₉O₃₆ represents a new structure type, characterized by MoO₄-tetrahedrons and three times capped trigonal prisms around La³⁺. Cu⁺ shows coordination numbers 2 + 1 or 2 + 2.     

Preparation of lithium fast ionic conductor by sol-gel-hydrothermal method

The solid fast ionic conductor was synthesized by the sol-gel-hydrothermal method. The influences of the dispersion reagent, the alkalinity and the calcination temperature on the surface morphology of nanopowders, and the electric conductivity were discussed. When PEG 12000 was used as the dispersion reagent, the alkalinity was 1.0% and the calcination temperature was 550°C; the electric conductivity at ambience temperature of the inorganic nanopowder of lithium fast ionic conductor synthesized was 2.59 × 10⁻³ S·cm⁻¹. __________ Translated from Journal of National University of Defense Technology, 2005, 27(2) (in Chinese)     

La2Mo2O9在低氧分压条件下的电导率及热膨胀测试

The electrical conductivity and thermal expansion of La2Mo2O9 under low oxygen partial pressure were studied with the help of thermoelectric power and dilatometric measurements, respectively. The ionic conduction of La2Mo2O9 was predominant with the electronic transference number less than 0.05 above an oxygen partial pressure of about Po2=10^-7 Pa at 700℃, and below this pressure the electronic conduction became obvious. The defect reaction and small polaron hopping among molybdenum sites were proposed to explain the electronic conduction. Accompanying the phase transition, there was a sharp increase of thermal expansion, which became more serious under low oxygen partial pressure. The substitution of lanthanum by neodymium led to the increase of electrical conductivity but the decrease of phase stability.     

Structure determination of low-dimensional conductor sodium molybdenum purple bronze Na0.9Mo6O17

Structure determination of the molybdenum purple bronze Na_0.9Mo₆O₁₇ is carried out by single-crystal X-ray diffraction. The crystal is monoclinic with space group A2 and the lattice constants are a = 12.983(2), b = 5.518(1), c = 9.591(2) Å, β = 89.94(1)°, Z = 2. Full-matrix least-squares refinement gives the final values of R(F) = 0.028 and R_w(F) = 0.040 for 1484 independent reflections, in which the occupancy factor of the sodium atom becomes 0.899(12). The present structure is built up of the linkage of the MoO₄ and MoO₆ polyhedra. There are slabs which consist of four layers of distorted MoO₆ octahedra sharing corners. Both the structure and the molybdenum valence distribution estimated from the MoO bond lengths are considered to lead to the two-dimensional electronic transport. This structure is compared with those of other members of molybdenum purple bronzes, K_0.9Mo₆O₁₇ and Li_0.9Mo₆O₁₇. The difference of the electronic properties among these compounds can be well understood on the basis of their structural characteristics.     

室温离子液体催化巯基乙酸异辛酯的合成

巯基乙酸异辛酯是一种广泛应用于精细化工、树脂和塑料制造的中间体,尤其在聚氯乙烯无毒制品中有着重要用途[1],其合成方法的改进也成为研究的主要课题之一。巯基乙酸异辛酯的合成通常采用硫酸催化法[2],由于浓硫酸污染环境、腐蚀设备,特别是近年来环保法规对环境和安全性不断提高的要求,用固体酸(分子筛、离子交换树脂、固体超强酸)等取代H2SO4、HF、A lC l3等强腐蚀性酸作为催化剂的催化工艺获得明显进展[3],但这些催化剂也有自身的缺点[4]。室温离子液体是近年来受到极大关注的一类新材料,它为人们探索环境友好的催化体系和溶剂提供了…     

Structure and dynamics of the fast lithium ion conductor "Li7La3Zr2O12"

The solid lithium-ion electrolyte "Li(7)La(3)Zr(2)O(12)" (LLZO) with a garnet-type structure has been prepared in the cubic and tetragonal modification following conventional ceramic syntheses routes. Without aluminium doping tetragonal LLZO was obtained, which shows a two orders of magnitude lower room temperature conductivity than the cubic modification. Small concentrations of Al in the order of 1 wt% were sufficient to stabilize the cubic phase, which is known as a fast lithium-ion conductor. The structure and ion dynamics of Al-doped cubic LLZO were studied by impedance spectroscopy, dc conductivity measurements, (6)Li and (7)Li NMR, XRD, neutron powder diffraction, and TEM precession electron diffraction. From the results we conclude that aluminium is incorporated in the garnet lattice on the tetrahedral 24d Li site, thus stabilizing the cubic LLZO modification. Simulations based on diffraction data show that even at the low temperature of 4 K the Li ions are blurred over various crystallographic sites. This strong Li ion disorder in cubic Al-stabilized LLZO contributes to the high conductivity observed. The Li jump rates and the activation energy probed by NMR are in very good agreement with the transport parameters obtained from electrical conductivity measurements. The activation energy E(a) characterizing long-range ion transport in the Al-stabilized cubic LLZO amounts to 0.34 eV. Total electric conductivities determined by ac impedance and a four point dc technique also agree very well and range from 1 × 10(-4) Scm(-1) to 4 × 10(-4) Scm(-1) depending on the Al content of the samples. The room temperature conductivity of Al-free tetragonal LLZO is about two orders of magnitude lower (2 × 10(-6) Scm(-1), E(a) = 0.49 eV activation energy). The electronic partial conductivity of cubic LLZO was measured using the Hebb-Wagner polarization technique. The electronic transference number t(e-) is of the order of 10(-7). Thus, cubic LLZO is an almost exclusive lithium ion conductor at ambient temperature.     

Nonstoichiometric La(2 - x)GeO(5 - delta) monoclinic oxide as a new fast oxide ion conductor.

Oxide ion conductivity in La(2)GeO(5)-based oxide was investigated and it was found that La-deficient La(2)GeO(5) exhibits oxide ion conductivity over a wide range of oxygen partial pressure. The crystal structure of La(2)GeO(5) was estimated to be monoclinic with P2(1)/c space group. Conductivity increased with increasing the amount of La deficiency and the maximum value was attained at x = 0.39 in La(2 - x)GeO(5 - delta). The oxide ion transport number in La(2)GeO(5)-based oxide was estimated to be unity by the electromotive force measurement in H(2)-O(2) and N(2)-O(2) gas concentration cells. At a temperature higher than 1000 K, the oxide ion conductivity of La(1.61)GeO(5 - delta) was almost the same as that of La(0.9)Sr(0.1)Ga(0.8)Mg(0.2)O(3 - delta) or Ce(0.85)Gd(0.15)O(2 - delta), which are well-known fast oxide ion conductors. On the other hand, a change in the activation energy for oxide ion conductivity was observed at 973 K, and at intermediate temperature, the oxide ion conductivity of La(1.61)GeO(5 - delta) became much smaller than that of these well-known fast oxide ion conductors. The change in the activation energy of the oxide ion conductivity seems to be caused by a change in the local oxygen vacancy structure. However, doping a small amount of Sr for La in La(2)GeO(5) was effective to stabilize the high-temperature crystal structure to low temperature. Consequently, doping a small amount of Sr increases the oxide ion conductivity of La(2)GeO(5)-based oxide at low temperature.     

Low temperature structural phase transition of Ba3NaIr2O9

Single crystal X-ray and synchrotron X-ray powder diffraction have been used to probe the structure of Ba₃NaIr₂O₉ from 300 K down to 20 K. Ba₃NaIr₂O₉ is found to undergo a structural transition from hexagonal symmetry, P6₃/mmc, at ambient temperature to monoclinic symmetry, C2/c, at low temperature. The evolution of the unit cell volume upon cooling is indicative of a higher order structural transition, and the symmetry breaking becomes apparent as the temperature is decreased. The low temperature monoclinic structure of Ba₃NaIr₂O₉ contains strongly distorted [NaO₆] and [IrO₆] octahedra in comparison to the room temperature hexagonal structure.     

Ion dynamics in Ba-, Sr-, and Ca-doped La2Mo2O9 from analysis of ac impedance

Conductivity measurement on alkaline earth-doped La₂Mo₂O₉ is well documented, but the ion dynamic study of this material is scarcely reported. Alternating current impedance measurement of Ba-, Sr-, and Ca-doped La₂Mo₂O₉ in the light of ion dynamics has been discussed. The low-temperature regime, 250 °C to 500 °C, has been selected for study on the basis of frequency dispersion of conductivity as well as in terms of modulus formalism. The values of exponential parameter, s, of universal dielectric response and the stretching exponent, β, of Kohlrausch–Williams–Watts relation are evaluated from curve fitting. Scaling behavior of the doped materials has also been investigated. Temperature dependence of such parameters is checked and is interpreted for the plausible mechanism of ionic motion in the material at low temperature.