Lithium tetrahydridoaluminate LiAlH4 and hexahydridoaluminate Li3AlH6: molar heat capacity and thermodynamic properties from 10 to 300 K

The heat capacity of lithium tetra- and hexa-hydridoaluminate have been determined by adiabatic calorimetry over the range 10 to 300 K and associated thermodynamic functions have been computed. At 298.15 K the heat capacities C_p and entropies S^o are respectively 83.19 J K^?1 mol^?1 and 78.8 J K^?1 mol^?1 for LiAlH₄ and 127.75 J K^?1 mol^?1 and 102.6 J K^?1 mol^?1 for Li₃AlH₆.     

A new diatomics-in-molecules study of Li3 and Li4

The diatomics-in-molecules method, with an improved triplet diatomic curve for Li₂, is employed in a reexamination of the stability of Li₃ and Li₄ species. Results are compared to other theoretical and experimental values.     

High pressure induced coordination evolution in chain compound Li2CuO2

Using diamond anvil cell technique with angle dispersive X-ray diffraction (ADXD) of synchrotron radiation and electrical conductivity measurements, we have observed that CuO₂ chain compound Li₂CuO₂ transforms from ambient orthorhombic symmetry into a new phase at above 5.4 GPa and room temperature. The new phase was found to be of monoclinic structure with an increased oxygen coordination number of Cu²⁺ from four at ambient to six at high pressure that provides a structural basis of the evolution of principle physical properties. The high pressure phase of Li₂CuO₂ is discussed in line with the first principle calculations.     

Structure and properties of ordered Li2IrO3 and Li2PtO3

The structures of Li₂MO₃ (M=Ir, Pt) can be derived from the well-known Li-ion battery cathode material, LiCoO₂, through ordering of Li⁺ and M⁴⁺ ions in the layers that are exclusively occupied by cobalt in LiCoO₂. The additional cation ordering lowers the symmetry from rhombohedral (R-3m) to monoclinic (C2/m). Unlike Li₂RuO₃ no evidence is found for a further distortion of the structure driven by formation of metal-metal bonds. Thermal analysis studies coupled with both ex-situ and in-situ X-ray diffraction measurements show that these compounds are stable up to temperatures approaching 1375 K in O₂, N₂, and air, but decompose at much lower temperatures in forming gas (5% H₂:95% N₂) due to reduction of the transition metal to its elemental form. Li₂IrO₃ undergoes a slightly more complicated decomposition in reducing atmospheres, which appears to involve loss of oxygen prior to collapse of the layered Li₂IrO₃ structure. Electrical measurements, UV-visible reflectance spectroscopy and electronic band structure calculations show that Li₂IrO₃ is metallic, while Li₂PtO₃ is a semiconductor, with a band gap of 2.3 eV.     

Effect of high hydrostatic pressure on structural stability of Ti3GeC2: A first-principles investigation

An investigation into the structural stability, electronic and elastic properties of Ti₃GeC₂ under high hydrostatic pressure was conducted using first-principles calculations based on density functional theory (DFT). From the energy and enthalpy calculations, and the variations of elastic constants with pressure, we conclude that α‐Ti₃GeC₂ is most stable upon compression to 100 GPa, which is not consistent with the nonhydrostatic in situ synchrotron X-ray diffraction studies. The higher structural stability was analyzed in terms of electronic level. The absence of band gap at the Fermi level and the finite value of the density of states at the Fermi energy reveal the metallic behavior of all polymorphs of Ti₃GeC₂.     

Ab initio structure determination of new compound Li4CaB2O6

A new compound, Li₄CaB₂O₆, has been synthesized by solid-state reaction and its structure has been determined from powder X-ray diffraction data by direct methods. The refinement was carried out using the Rietveld methods and the final refinement converged with R_p=10.4%, R_wp=14.2%, R_exp=4.97%. This compound belongs to the orthorhombic space group Pnnm, with lattice parameters a=9.24036(9) Å, b=8.09482(7) Å, and c=3.48162(4) Å. Fundamental building units are isolated [BO₃]³⁻ anionic groups, which are all parallel to the a-b plane stacked along the c-axis. The Ca atoms are six-coordinated by the O atoms to form octahedral coordination polyhedra, which are joined together through edges along the c-axis, forming infinitely long three-dimensional chains. The Li atoms have a four-fold and a five-fold coordination with O atoms that lead to complex Li-O-Li chains that also extend along the c-axis. The infrared spectrum of Li₄CaB₂O₆ was also studied, which is consistent with the crystallographic study.     

Kinetic analysis of the thermal stability of lithium silicates (Li4SiO4 and Li2SiO3)

The kinetics describing the thermal decomposition of Li₄SiO₄ and Li₂SiO₃ have been analysed. While Li₄SiO₄ decomposed on Li₂SiO₃ by lithium sublimation, Li₂SiO₃ was highly stable at the temperatures studied. Li₄SiO₄ began to decompose between 900 and 1000 °C. However, at 1100 °C or higher temperatures, Li₄SiO₄ melted, and the kinetic data of its decomposition varied. The activation energy of both processes was estimated according to the Arrhenius kinetic theory. The energy values obtained were −408 and −250 kJ mol⁻¹ for the solid and liquid phases, respectively. At the same time, the Li₄SiO₄ decomposition process was described mathematically as a function of a diffusion-controlled reaction into a spherical system. The activation energy for this process was estimated to be −331 kJ mol⁻¹. On the other hand, Li₂SiO₃ was not decomposed at high temperatures, but it presented a very high preferential orientation after the heat treatments.     

Structure, thermal stability and properties of Li3Sc(BO3)2

Polycrystalline Li₃Sc(BO₃)₂ was synthesized through the solid-state reaction, which is air-, water- and thermal-stable below about 929 °C. Its crystal structure was resolved and refined on the basis of powder X-ray diffraction data. The metal-borate framework is built up from ScO₆ octahedra connected to each other by sharing common edges, corners and faces of BO₃ units and LiO₄ groups. Coordination surrounding of B-O in this structure, [BO₃]³⁻ group, was confirmed by an infrared absorption spectrum of an Li₃Sc(BO₃)₂. According to the electronic structure calculated by first-principles calculations, an Li₃Sc(BO₃)₂ is an insulator with a wide indirect energy band gap of about 4.4 eV. Considering the facile synthesis, large band gap, and thermal stability and excellent Tb³⁺-doped photoluminescence characteristics of this compound in general, it may be a good candidate as host of phosphors deposited on chip of the light-emitting diodes for white-color conversion.     

Superconductivity in Li3Ca2C6 intercalated graphite

In this paper, we report the discovery of superconductivity in Li₃Ca₂C₆. Several graphite intercalation compounds (GICs) with electron donors, are well known as superconductors [T. Enoki, S. Masatsugu, E. Morinobu, Graphite Intercalation Compounds and Applications, Oxford University Press, Oxford, 2003]. It is probably not astonishing, since it is generally admitted that low dimensionality promotes high superconducting transition temperatures. Superconductivity is lacking in pristine graphite, but after charging the graphene planes by intercalation, its electronic properties change considerably and superconducting behaviour can appear. Li₃Ca₂C₆ is a ternary GIC [S. Pruvost, C. Hérold, A. Hérold, P. Lagrange, Eur. J. Inorg. Chem. 8 (2004) 1661-1667], for which the intercalated sheets are very thick and poly layered (five lithium layers and two calcium ones). It contains a great amount of metal (five metallic atoms for six carbon ones). Its critical temperature of 11.15 K is very close to that of CaC₆ GIC [T.E. Weller, M. Ellerby, S.S. Saxena, R.P. Smith, N.T. Skipper, Nat. Phys. 1 (2005) 39-41; N. Emery, C. Hérold, M. d’Astuto, V. Garcia, Ch. Bellin, J.F. Marêché, P. Lagrange, G. Loupias, Phys. Rev. Lett. 95 (2005) 087003] (11.5 K). Both CaC₆ and Li₃Ca₂C₆ GICs possess currently the highest transition temperatures among all the GICs.     

溶胶凝胶法合成Li3V6O16及其电化学性能研究

本文以双氧水为配位剂,以CH3COOLi·2H2O和V2O5为原料,采用溶胶凝胶法合成了一种新型的晶体Li3V6O16。随后分别采用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和电子衍射(SAED)、X光电子能谱(XPS)和充放电测试等手段对材料进行了表征。SEM观察表明,产物主要是表面比较光滑的纳米片状晶体,TEM和SAED研究都证实了XRD和SEM的研究结果。充放电测试结果表明,该物质具有较高的比容量、良好的可逆性和循环稳定性。     

Etude par RMN de la mobilité du lithium dans trois oxydes à structure pseudo-bidimensionnelle: Li8SnO6, Li7NbO6 et Li6In2O6

The lithium ion mobility in three solid electrolytes (Li₈SnO₆, Li₇NbO₆, and Li₆In₂O₆) has been studied by NMR at several resonance frequencies from 170 to 500°K. The ⁷Li quadrupolar lineshape evolution shows the predominant influence on the conductivity mechanism of the vacancies in the octahedral sites of the oxygen close packing. In Li₈SnO₆, which has no vacancies, the lithium ions situated in the tetrahedral sites have the highest mobility. Spin-lattice relaxation times are in good agreement with the hypothesis of a Li₇NbO₆ 2D conductivity. The values of the activation energy, increasing from Li₇NbO₆ to Li₆In₂O₆ and to Li₈SnO₆, are found to be three times lower than those obtained from conductivity measurements.     

Low-temperature structural determination of anhydrous Li2SeO4

Anhydrous Li₂SeO₄ crystallizes in the trigonal space group $\text{R}\text{3}$ with a = 13.931(2), c = 9.304(3) Å, V = 1563.7 ų, Z = 18, D_c = 2.988 g cm^?3. The unit cell transforms to the rhombohedral coordinate system as a = 8.620 Å, α = 107.81(2)°, V = 521.2 ų, Z = 6. The structure contains selenate anions bridged by Li in the phenacite structural type. Data collection was performed at low temperature for precise placement of the Li cations which are tetrahedrally surrounded by oxygen atoms. Some problems with secondary extinction were apparent and a correction was made. The structure refined to an R value of 0.034.     

LaNiO3的焙烧温度对甲醇水蒸气重整制氢CuO/LaNiO3催化剂的影响

采用溶胶凝胶法合成了LaNiO_3钙钛矿型氧化物载体,再采用浸渍法制备了CuO/LaNiO_3催化剂,并通过XRF、XRD、BET、H_2-TPR和XPS等手段对催化剂进行了表征,考察了LaNiO_3钙钛矿的焙烧温度对CuO/LaNiO_3催化剂结构及其催化甲醇水蒸气重整制氢性能的影响。结果表明,载体焙烧温度主要影响了催化剂的表面晶格氧缺位,活性组分和载体间的相互作用。当载体焙烧温度为800℃时,催化剂表面氧空穴较多,活性组分与载体间相互作用较强,因此,催化甲醇水蒸气重整制氢活性较好。     

Syntheses and structures of Li3ScF6 and high pressure LiScF4−, luminescence properties of LiScF4, a new phase in the system LiF-ScF3

Colorless single crystals of Li₃ScF₆ have been prepared by reacting the binary components LiF and ScF₃ at 820 °C for 16 h in argon atmosphere. This complex fluoride is the only stable phase in the system LiF-ScF₃ under ambient pressure. According to a structure refinement based on single crystal X-ray diffraction data it crystallizes in the centrosymmetric space group with and . The new structure of Li₃ScF₆ is a filled variant of the Na₂GeF₆ type structure and can be described in terms of a hexagonal close packing of fluorine in which 2/3 of the octahedral holes are occupied by Sc and Li.High pressure/high temperature studies of the system LiF-ScF₃ show that the new phase LiScF₄ is formed at around 5.5 GPa and 575 °C. According to Rietveld refinements of powder X-ray diffraction data LiScF₄ adopts the Scheelite type structure (space group I4₁/a) with and . A sample of LiScF₄ doped with 1% Er exhibits an intense luminescence in the far IR region.     

High-pressure structure of Li2CO3

The high-pressure behavior of Li₂CO₃ is studied up to 25 GPa with synchrotron angle-dispersive powder X-ray diffraction in diamond anvil cells and synthesis using a multi-anvil apparatus. A new non-quenchable hexagonal polymorph (P6₃/mcm, Z=2) occurs above 10 GPa with carbonate groups in a staggered configuration along the c-axis—a=4.4568(2) Å and c=5.1254(6) Å at 10 GPa. Two columns of face-shared distorted octahedra around the Li atoms are linked through octahedral edges. The oxygen atoms are coordinated to one carbon atom and four lithium atoms to form a distorted square pyramid. Splittings of X-ray reflections for the new polymorph observed above about 22 GPa under non-hydrostatic conditions arise from orthorhombic or monoclinic distortions of the hexagonal lattice. The results of this study are discussed in relation to the structural features found in other Me₂CO₃ carbonates (Me: Na, K, Rb, Cs) at atmospheric conditions.     

High temperature structural investigation of the delafossite type compound CuAlO2

Crystal structure parameters were determined for the delafossite type compound CuAlO₂ at 295, 450, 600, 750, 900, and 1200 K with single crystal high temperature X-ray diffraction technique. Anisotropic refinements result in conventional R values of 0.021, 0.027, 0.029, 0.030, 0.032, and 0.036 at respective temperatures. Crystals of CuAlO₂ have the rhombohedral space group $\text{R}\text{3}\text{m}$ with a = 2.8584(7), c = 16.958(3) Å and Z = 3 at 295 K. The mean thermal expansion coefficient for the dimension a is 11.0 × 10^?6 K^?1 about three times larger than 4.1 × 10^?6 K^?1 for c. In the structure, the AlO₆ octahedra are linked by their OO edges and form AlO₂ layers perpendicular to the c axis with the thickness corresponding to the height of an octahedron. With increasing temperature, the AlO₆ octahedra expand along the directions of the basal plane, while expansion scarcely occurs along the c axis. The Cu atom lying between the AlO₂ layers shows a large anisotropic behavior in the thermal vibration. The temperature factor for Cu atom in the basal plane becomes very large (0.044 Ų) at 1200 K, but the ratio of the temperature factor perpendicular to c to that parallel to c does not change appreciably with increasing temperature.     

Phase relations and thermodynamic properties in the ternary reciprocal system LiFNaFNa3AlF6Li3AlF6

The ternary reciprocal sytem LiFNaFNa₃AlF₆Li₃AlF₆ has been investigated by thermal analysis, differential thermal analysis, quenching, X-ray diffraction, microscopy, and calorimetry. The phase diagrams of the following systems are given: LiFNaF (revised), LiFAlF₃, Na₃AlF₆LiF, and LiFNaFNa₃AlF₆Li₃AlF₆. Some values of heat of mixing and heat content in the system have been measured.It is shown that molten mixtures in this system can be treated as consisting of the following species: Li⁺, Na⁺, AlF^3-₆, AlF₃ and F^-. At high contents of alkali fluoride the dissociation of the AlF^3-₆ ion to AlF₃ and F^- will, however, be negligible.On the basis of the calorimetric data, heats of mixing and dissociation, together with the degree of dissociation of AlF^3-₆, in the systems LiFAlF₃ and LiFNa₃AlF₆ have been calculated. The partial Gibbs free energy, enthalpy and entropy of Na₃AlF₆ in the system LiFNa₃AlF₆ have also been calculated. Finally the activity of Na₃AlF₆ in the latter system has been calculated by treating it as a part of the ternary reciprocal system 3LiF+Na₃AlF₆→Li₃AlF₆+3NaFA satisfactory agreement between the Flood, Førland and Grjotheim theory and the experimental values is obtained at small Na₃AlF₆ concentrations.     

Effect of sintering on the ionic conductivity of garnet-related structure Li5La3Nb2O12 and In- and K-doped Li5La3Nb2O12

Garnet-structure related metal oxides with the nominal chemical composition of Li₅La₃Nb₂O₁₂, In-substituted Li_5.5La₃Nb_1.75In_0.25O₁₂ and K-substituted Li_5.5La_2.75K_0.25Nb₂O₁₂ were prepared by solid-state reactions at 900, 950, and 1000 °C using appropriate amounts of corresponding metal oxides, nitrates and carbonates. The powder XRD data reveal that the In- and K-doped compounds are isostructural with the parent compound Li₅La₃Nb₂O₁₂. The variation in the cubic lattice parameter was found to change with the size of the dopant ions, for example, substitution of larger In³⁺(r_CN6: 0.79 Å) for smaller Nb⁵⁺ (r_CN6: 0.64 Å) shows an increase in the lattice parameter from 12.8005(9) to 12.826(1) Å at 1000 °C. Samples prepared at higher temperatures (950, 1000 °C) show mainly bulk lithium ion conductivity in contrast to those synthesized at lower temperatures (900 °C). The activation energies for the ionic conductivities are comparable for all samples. Partial substitution of K⁺ for La³⁺ and In³⁺ for Nb⁵⁺ in Li₅La₃Nb₂O₁₂ exhibits slightly higher ionic conductivity than that of the parent compound over the investigated temperature regime 25-300 °C. Among the compounds investigated, the In-substituted Li_5.5La₃Nb_1.75In_0.25O₁₂ exhibits the highest bulk lithium ion conductivity of 1.8×10⁻⁴ S/cm at 50 °C with an activation energy of 0.51 eV. The diffusivity (“component diffusion coefficient”) obtained from the AC conductivity and powder XRD data falls in the range 10⁻¹⁰-10⁻⁷ cm²/s over the temperature regime 50-200 °C, which is extraordinarily high and comparable with liquids. Substitution of Al, Co, and Ni for Nb in Li₅La₃Nb₂O₁₂ was found to be unsuccessful under the investigated conditions.     

Crystal growth, structural characterization and magnetic properties of Ca3CuRhO6, Ca3Co1.34Rh0.66O6 and Ca3FeRhO6

Single crystals of Ca₃CuRhO₆, Ca₃Co_1.34Rh_0.66O₆ and Ca₃FeRhO₆ were synthesized by high temperature flux growth in molten K₂CO₃ and structurally characterized by single crystal X-ray diffraction. While Ca₃Co_1.34Rh_0.66O₆ and Ca₃FeRhO₆ crystallize with trigonal (rhombohedral) symmetry in the space group , Z=6: Ca₃Co_1.34Rh_0.66O₆a=9.161(1) Å, c=10.601(2) Å; Ca₃FeRhO₆a=9.1884(3) Å, c=10.7750(4) Å; Ca₃CuRhO₆ adopts a monoclinic distortion of the K₄CdCl₆ structure in the space group C2/c, Z=4: a=9.004(2) Å, b=9.218(2) Å, c=6.453(1) Å, β=91.672(5). All crystals of Ca₃CuRhO₆ examined were twinned by pseudo-merohedry. Ca₃CuRhO₆, Ca₃Co_1.34Rh_0.66O₆, and Ca₃FeRhO₆ are structurally related and contain infinite one-dimensional chains of alternating face-sharing RhO₆ octahedra and MO₆ trigonal prisms. In the monoclinic modification, the copper atoms are displaced from the center of the trigonal prism toward one of the rectangular faces adopting a pseudo-square planar configuration. The magnetic properties of Ca₃CuRhO₆, Ca₃Co_1.34Rh_0.66O₆, and Ca₃FeRhO₆ are discussed.