Effect of pressure and temperature on structural stability of potential hydrogen storage compound Li3AlH6

The crystal structure of Li₃AlH₆ was investigated at high pressures upto 27 GPa using a diamond anvil cell with synchrotron radiation in addition to high temperature X-ray diffraction. Density functional theoretical (DFT) calculations were performed simultaneously. While the structure of Li₃AlH₆ is stable on increasing temperature, the results of high pressure experiments show a pressure induced phase transition from the ambient phase to a high pressure cubic phase around 10.6 GPa. The transition pressure of 10.6 GPa and the bulk modulus value B₀ = 32(2) GPa for the phase obtained are in good agreement with the theoretical results.     

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.     

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.     

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.     

Heat capacity of MnAs0.88P0.12 from 10 to 500 K: Thermodynamic properties and transitions

The heat capacity of MnAs_0.88P_0.12 has been measured by adiabatic shield calorimetry from 10 to 500 K. It is shown that very small energy changes are connected with two magnetic order-order transitions, indicating that these can be regarded as mainly “noncoupled” magnetic transitions. At higher temperatures contributions to the excess heat capacity arises from a magnetic order-disorder transition, a conversion from low- to high-spin state for manganese, and a MnP- to NiAs-type structural transition. The observed heat capacity is resolved into contributions from the different physical phenomena, and the character of the transitions is discussed. In particular it is substantiated that the dilational contribution, which includes magnetoelastic and magnetovolume terms as well as normal anharmonicity terms, plays a major role in MnAs_0.88P_0.12. The entropy of the magnetic order-disorder transition is smaller than should be expected from a complete randomization of the spins, assuming a purely magnetic transition. Thermodynamic functions have been evaluated and the respective values of C_p, {S^O_m(T) - S^O_m(0)}, and -{G^O_m(T) - H^O_m(0)}/T at 298.15 K are 68.74, 72.09, and 32.30 J K⁻¹ mole⁻¹, and at 500 K 56.05, 108.12, and 56.64 J K⁻¹ mole⁻¹.     

Cesium chromate,Cs2CrO4: heat capacity and thermodynamic properties from 5 to 350 K

The heat capacity of a sample of Cs₂CrO₄ was determined in the temperature range 5 to 350 K by aneroid adiabatic calorimetry. The heat capacity at constant pressure C_p^o(298.15 K), the entropy S^o(298.15 K), the enthalpy {H^o(298.15 K) - H^o(0)} and the function $\text{? {G}{}^{\mathrm{o}}\text{(298.15}\text{K}\text{) - H}{}^{\mathrm{o}}\text{(0)}}\text{298.15}\text{K}$ were found to be (146.06 ± 0.15) J K^?1 mol^?1, (228.59 ± 0.23) J K^?1 mol^?1, (30161 ± 30) J mol^?1, and (127.43 ± 0.13) J K^?1 mol^?1, respectively. The heat capacity C_p^o(298.15 K) and entropy S^o(298.15 K) and entropy S^o(298.15 K) of Rb₂CrO₄ are estimated to be (146.0 ± 1.0) J K^?1 mol^?1 and (217.6 ± 3.0) J K^?1 mol^?1, respectively.     

Heat capacity and thermodynamic properties of crystalline ornidazole (C7H10ClN3O3)

The molar heat capacities of 1-(2-hydroxy-3-chloropropyl)-2-methyl-5-nitroimidazole (Ornidazole) (C₇H₁₀ClN₃O₃) with purity of 99.72 mol% were measured with an adiabatic calorimeter in the temperature range between 79 and 380 K. The melting-point temperature, molar enthalpy, Δ_fusH_m, and entropy, Δ_fusS_m, of fusion of this compound were determined to be 358.59±0.04 K, 21.38±0.02 kJ mol⁻¹ and 59.61±0.05 J K⁻¹ mol⁻¹, respectively, from fractional melting experiments. The thermodynamic function data relative to the reference temperature (298.15 K) were calculated based on the heat capacities measurements in the temperature range from 80 to 380 K. The thermal stability of the compound was further investigated by DSC and TG. From the DSC curve an intensive exothermic peak assigned to the thermal decomposition of the compound was observed in the range of 445-590 K with the peak temperature of 505 K. Subsequently, a slow exothermic effect appears when the temperature is higher than 590 K, which is probably due to the further decomposition of the compound. The TG curve indicates the mass loss of the sample starts at about 440 K, which corresponds to the decomposition of the sample.     

Zeolite 4A: heat capacity and thermodynamic properties

The heat capacity of zeolite 4A (also known as LTA, Linde Type A and sodium zeolite A), in the temperature range from 37 to 311 K, is reported. The heat capacity shows no anomalies in this temperature range. Thermodynamic parameters, H, S and G, relative to their values at T=0 K were derived. From these data, we find that zeolite 4A is stabilized by strong enthalpic interactions. Furthermore, its thermodynamic stability results from the strong Si---O and Al---O bonds in the primary building units, with bond strengths very close to those in other similar materials.     

WCl6/LiAlH4 Promoted transformation of imines into secondary and tertiary amines

The reaction of WCl₆/LiAlH₄ with imines, R′NCHR, gave tertiary amines, R′N(CH₂R)₂, and secondary amines, R′NHCHRCH₂R. Isotope labeling experiments revealed that the reaction involved two types of azatungstenacyclobutanes, $\text{WNR′CHRC}$HR and $\text{WCHRNR′C}$HR, produced from the reaction of an alkylidene tungsten intermediate with the imine CN double bond. Formation of these metallacyclobutanes is highly dependent on the solvent used.     

Low temperature structural variations and molar heat capacity of stolzite, PbWO4

The crystal structure, thermal expansion and heat capacity of PbWO₄ (mineral name stolzite) scintillator material were comprehensively studied over a wide temperature range. No phase transitions were found down to 2 K (I4₁/a, scheelite structure type). A distinct feature of the temperature induced structural variations in PbWO₄ are the different thermal elongations of shorter and longer Pb-O distances. The low-temperature thermal expansion of PbWO₄ was parameterized on the basis of the 1st order Grüneisen approximation using a Debye function for the internal energy with a Debye temperature of 237 K, a bulk modulus of 67 GPa and a Grüneisen parameter of 1.08. The expansion along the c-axis is about 2.5-3 times higher in the range 23-290 K than along the a-direction. This pronounced anisotropy of the thermal expansion arises from the arrangements of rigid tetrahedral WO₄²⁻ units along 〈100〉-directions while Pb²⁺ cations occupy the sites between WO₄²⁻ in 〈001〉-directions.     

Li+ ion conductivity in the system Li4SiO4Li3VO4

Two ranges of solid solutions were prepared in the system Li₄SiO₄Li₃VO₄: Li_4?xSi_1?xV_xO₄, 0 < x ? 0.37 with the Li₄SiO₄ structure and Li_3+yV_1?ySi_yO₄, 0.18 ? y ? 0.53 with a γ structure. The conductivity of both solid solutions is much higher than that of the end members and passes through a maximum at ～40Li₄SiO₄ · 60Li₃VO₄ with values of ～1 × 10^?5 ohm^?1 cm^?1 at 20°C, rising to ～4 × 10^?2 ohm^?1 cm^?1 at 300°C. These conductivities are several times higher than in the corresponding Li₄SiO₄Li₃(P,As)O₄ systems, especially at room temperature. The solid solutions are easy to prepare, are stable in air, and maintain their conductivity with time. The mechanism of conduction is discussed in terms of the random-walk equation for conductivity and the significance of the term c(1 ? c) in the preexponential factor is assessed. Data for the three systems Li₄SiO₄Li₃YO₄ (Y = P, As. V) are compared.     

Crystal structure and magnetic properties of Li,Cr-containing molybdates Li3Cr(MoO4)3, LiCr(MoO4)2 and Li1.8Cr1.2(MoO4)3

Single crystals of LiCr(MoO₄)₂, Li₃Cr(MoO₄)₃ and Li_1.8Cr_1.2(MoO₄)₃ were grown by a flux method during the phase study of the Li₂MoO₄-Cr₂(MoO₄)₃ system at 1023 K. LiCr(MoO₄)₂ and Li₃Cr(MoO₄)₃ single phases were synthesized by solid-state reactions. Li₃Cr(MoO₄)₃ adopts the same structure type as Li₃In(MoO₄)₃ despite the difference in ionic radii of Cr³⁺ and In³⁺ for octahedral coordination. Li₃Cr(MoO₄)₃ is paramagnetic down to 7 K and shows a weak ferromagnetic component below this temperature. LiCr(MoO₄)₂ is isostructural with LiAl(MoO₄)₂ and orders antiferromagnetically below 20 K. The magnetic structure of LiCr(MoO₄)₂ was determined from low-temperature neutron diffraction and is based on the propagation vektor . The ordered magnetic moments were refined to 2.3(1) μ_B per Cr-ion with an easy axis close to the [1 1 1¯] direction. A magnetic moment of 4.37(3) μ_B per Cr-ion was calculated from the Curie constant for the paramagnetic region.The crystal structures of the hitherto unknown Li_1.8Cr_1.2(MoO₄)₃ and LiCr(MoO₄)₂ are compared and reveal a high degree of similarity: In both structures MoO₄-tetrahedra are isolated from each other and connected with CrO₆ and LiO₅ via corners. In both modifications there are Cr₂O₁₀ fragments of edge-sharing CrO₆-octahedra.     

Synthesis and thermodynamic properties of a metal-organic framework: [LaCu6(μ-OH)3(Gly)6im6](ClO4)6

A metal-organic complex, which has the potential property of absorbing gases, [LaCu₆(μ-OH)₃(Gly)₆im₆](ClO₄)₆ was synthesized through the self-assembly of La³⁺, Cu²⁺, glycine (Gly) and imidazole (Im) in aqueous solution and characterized by IR, element analysis and powder XRD. The molar heat capacity, C_p,m, was measured from T = 80 to 390 K with an automated adiabatic calorimeter. The thermodynamic functions [H_T − H_298.15] and [S_T − S_298.15] were derived from the heat capacity data with temperature interval of 5 K. The thermal stability of the complex was investigated by differential scanning calorimetry (DSC).     

Magnetic behavior of spin-chain compounds, Sr3ZnRhO6 and Ca3NiMnO6, from heat capacity and AC susceptibility studies

Heat-capacity (C) and ac susceptibility measurements have been performed on the spin-chain compounds, Sr₃ZnRhO₆ and Ca₃NiMnO₆, to establish their magnetic behavior and to explore whether there are magnetic frustration effects due to antiferromagnetic coupling of the chains arranged in a triangular fashion. While the paramagnetic Curie temperatures have been known to be large with a negative sign, as though antiferromagnetic interaction is very strong, the results establish that (i) the former apparently undergoes inhomogeneous magnetic ordering only around 15 K, however without spin-glass anomalies, and (ii) the latter orders antiferromagnetically at a relatively low temperature (17 K). Thus, the magnetic frustration manifests differently in these compounds.     

Metastable Equilibrium in Quaternary System Li2SO4 ＋ K2SO4＋Li2CO3 ＋ K2CO3 ＋ H2O at 288 K

IntroductionThe Zhabuye salt lake, Tibet in China, is famousfor the high concentrations of lithium, boron, andpotassium in the world. The main components areLi , K , Na , B4O72 -, CO32 -, Cl-, SO42 -, andH2O, including rare elements such as Rb and Cs .The…     

Preparation and crystal structure of Li2CaSiO4 and isostructural Li2CaGeO4

Li₂CaSiO₄ and Li₂CaGeO₄ are isostructural. They have body-centered tetragonal unit cells, with dimensions a = 5.047 ± 0.005, c = 6.486 ± 0.006 Å, and a = 5.141 ± 0.002, c = 6.595 ± 0.002 Å, respectively, and space group $\text{I}\text{4}\text{2m}$. Their crystal structures, refined to R = 0.076 and 0.051, respectively, comprise columns, parallel to [001], of alternating (CaO₈) dodecahedra and (SiO₄) [or (GeO₄)] tetrahedra that are linked by sharing edges. Neighboring columns are joined at their corners to form a three-dimensional network, enclosing channels parallel to [001] that contain lithium. The lithium atoms are in distorted (LiO₄) tetrahedra joined at the corners to form sheets perpendicular to [001].     

Electronic transitions in Li4CoCl4.10H2O

The electronic spectrum of Li₄CoCl₆.10H₂O was recorded at liquid nitrogen temperature in the 4,000–25,000 cm^?1 spectral region. The simi larity of this spectrum to that of CoCl₂ permitted us to assume O_h syn metry of the [CoCl₆]^4? cluster in our sample. The band assignment was performed in the crystal field approximation using Tanabe and Sugano's energy matrices for Dq = 730 cm^?1, B = 820 cm^?1 and C/B = 4.4.The large number of bands and high intensity of the maxima in the regio 19,000–21,000 cm^?1 is discussed.     

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.     

Synthesis, structure, solid-state thermolysis, and thermodynamic properties of new heterometallic complex Li2Co2(Piv)6(NEt3)2

The reaction of lithium pivalate, polymeric cobalt pivalate [Co(Piv)₂]_n, and triethylamine in THF at 60 °С afforded the new heterometallic antiferromagnetic complex Li₂Co₂(Piv)₆(NEt₃)₂ (2). The molecular and crystal structure of complex 2 was established and its magnetic behavior was studied. The vaporization and solid-state thermolysis of 2 were investigated. The thermodynamic characteristics of complex 2 were determined. The results of the present study show that complex 2 can be used as a potential molecular precursor for the synthesis of thin films of lithium cobaltate LiCoO₂.