Thermochemistry of C60 and C70 fullerene solvates

In an effort to improve understanding of dissolution behaviour of fullerenes and their simple chemical derivatives the binary systems of C₆₀, C₇₀ and the piperazine monoadduct of [60] fullerene C₆₀ N₂C₄H₈ with a series of aromatic solvents have been studied by means of DSC. In certain systems solid solvates have been found to be the thermodynamically stable phases relative to saturated solution at room temperature. Identified solid solvates were characterized by their compositions, temperatures and enthalpies of incongruent melting transitions. The regularities in thermodynamic stability of the solvated crystals have been discussed along with dissolution properties of fullerenes and the derivative. Certain correlations have been observed.     

Les systemes binaires AlPO4−M3PO4 (M=Li,Na, K)

The liquid-solid phase diagram of the binary systems AlPO₄?M₃PO₄(M=Li, Na, K) have been established. The additional compounds Na₃Al(PO₄)₂, Na₃Al₂(PO₄)₃ and K₃Al₂(PO₄)₃ have been found again. A new compound K₃Al(PO₄)₂ is observed. The melting point of Na₃PO₄ is 1545°C and K₃PO₄ does not melt up to 1700°C.     

Phase relations in the CoO–V<Subscript>2</Subscript>O<Subscript>5</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system in subsolidus area

Thermal properties of Co₂FeV₃O₁₁ have been reinvestigated. It has been proved that this compound does not exhibit polymorphism. It melts incongruently at the temperature of 770±5°C and the phase with lyonsite type structure is the solid product of this melting. Phase relations in the whole subsolidus area of the CoO–V₂O₅–Fe₂O₃ system have been determined. The solidus area projection onto the component concentration triangle plane of this system has been constructed using the DTA and XRD methods. 15 subsidiary subsystems can be distinguished in this system.     

Reactivity of Zn3V2O8 Towards ZnMoO4 in the Solid State

The reactivity of Zn₃ V₂ O₈ towards ZnMoO₄ was investigated by using DTA and XRD methods. A new compound of the formula Zn_2.5 VMoO₈ was found. It crystallises in an orthorhombic system. The melting temperature was determinated to be 845±5°C. This revised version was published online in August 2006 with corrections to the Cover Date.     

Heat capacity and thermodynamical properties of the crystal of [RE2(Glu)2(H2O)8](ClO4)4·H2O (RE = Nd, Eu, Dy)

Thermodynamical data of rare earth complexes with amino acid are important for engineering chemistry and fundamental chemistry. However, they have rarely been reported. In this work, a series of crystalline complexes of rare earth perchlorate coordinated with glutamic acid have been synthesized in water medium, and their thermodynamical data, including the heat capacity in low temperature range and the standard enthalpy of formation, were determined. These complexes were identified to be [RE₂(Glu)₂(H₂O)₈](ClO₄)₄·H₂O (RE = Nd, Eu, Dy) by using thermogravimetric analysis (TG), differential thermal analysis (DTA), and chemical and elementary analyses. Their purity has been determined. No melting points were observed for all the three complexes. The heat capacity of the complexes was measured by an adiabatic calorimeter from 79 to 370 K. Abnormal heat capacity values were detected for two of the complexes and the decomposition range of one complex was found. The temperature, enthalpy change and entropy change of the decomposition processes of the three complexes were calculated. The polynomial equations of heat capacity in the experimental temperature range have been obtained by least squares fitting. The standard enthalpy of formation was determined by an isoperibol reaction calorimeter at 298.15 K. Supported by the Research Fund of Beijing Institute of Petro-Chemical Technology (N06-06)     

Ion-beam irradiation of lanthanum compounds in the systems La2O3-Al2O3 and La2O3-TiO2

Thin crystals of La₂O₃, LaAlO₃, La_2/3TiO₃, La₂TiO₅, and La₂Ti₂O₇ have been irradiated in situ using 1 MeV Kr²⁺ ions at the Intermediate Voltage Electron Microscope-Tandem User Facility (IVEM-Tandem), Argonne National Laboratory (ANL). We observed that La₂O₃ remained crystalline to a fluence greater than 3.1×10¹⁶ ions cm⁻² at a temperature of 50 K. The four binary oxide compounds in the two systems were observed through the crystalline-amorphous transition as a function of ion fluence and temperature. Results from the ion irradiations give critical temperatures for amorphisation (T_c) of 647 K for LaAlO₃, 840 K for La₂Ti₂O₇, 865 K for La_2/3TiO₃, and 1027 K for La₂TiO₅. The T_c values observed in this study, together with previous data for Al₂O₃ and TiO₂, are discussed with reference to the melting points for the La₂O₃-Al₂O₃ and La₂O₃-TiO₂ systems and the different local environments within the four crystal structures. Results suggest that there is an observable inverse correlation between T_c and melting temperature (T_m) in the two systems. More complex relationships exist between T_c and crystal structure, with the stoichiometric perovskite LaAlO₃ being the most resistant to amorphisation.     

新铌酸盐化合物K6Zr2Nb14O42的合成

一些铌酸盐晶体具有优良的非线性光学性质,它们在激光倍频、电光调制、参量振荡、实时全息存贮等领域均具有潜在的广泛的应用前景,因此新铌酸盐晶体的人工合成、结构及性能研究工作受到了重视［１－３］,吴伯麟等曾报道了在Ｋ２Ｏ－Ｃｒ２Ｏ３－Ｎｂ２Ｏ５体系中存在一...     

Transparent oxyfluoride glass ceramics co-doped with Er and Yb - Crystallization and upconversion spectroscopy

Transparent glass ceramics in the system SiO₂-B₂O₃-PbO-CdO-PbF₂-CdF₂-YbF₃-ErF₃ showing infrared to visible anti-Stokes (upconversion) luminescence are studied in the present work. The glass compositions have been optimized in order to reduce the melting temperature and, hence, to obtain laboratory scale samples with good optical quality. Erbium-doped nanoscale Pb₄Yb₃F₁₇ crystals are precipitated in the precursor glasses during annealing at temperatures 30-40 K above T_g. A kinetically self-constrained growth explains the nano sizes of the crystals. Both the Stokes and anti-Stokes luminescence spectra of glasses could be explained with clustering of the Yb³⁺ and Er³⁺ ions in fluorine-rich regions. At the annealing temperature these regions act as nucleation precursors. The crystal growth further enhances the local concentration of these ions. Consequently, a series of energy transfer and energy cross relaxation processes occurs between adjacent rare earth ions leading to the observed luminescence spectra of the glass ceramics studied.     

Self-Assembled Structures of Diglycerol Monolaurate- and Monomyristate in Olive Oil

We have investigated the phase behavior and self-assembled structures of diglycerol monolaurate-and monomyristate (abbreviated as C₁₂G₂ and C₁₄G₂, respectivley) in olive oil over a wide range of temperatures and compositions. At lower temperatures, both the surfactants appear in solid state (α-solid), which does not swell with olive oil. The α-solid transforms into lamellar liquid crystal (L_α) phase upon heating and the solid melting temperature is practically constant at all surfactant/oil compositions, but the C₁₂G₂ melts earlier than the C₁₄G₂. There appear the dispersions of L_α phase and α-solid in the dilute regions of the C₁₂G₂/olive oil and the C₁₄G₂/olive oil systems, respectively, at 25°C. The L_α phase can solubilize some amount of olive oil, but as the oil concentration increases the excess oil separates out from the L_α phase, and there appears L_α dispersion in the dilute surfactant concentration region. The L_α phase eventually transforms into isotropic solutions (reverse micelles) with further heating. The structures (shape and size) of the reverse micelles have been characterized by small-angle x-ray scattering technique. It has found that the C₁₂G₂ and C₁₄G₂ surfactants form reverse rod-like micelles in olive oil above the L_α melting temperature and the micellar size increases with surfactant concentration, but decreases with temperatures.     

采用复合锂源制备的LiFePO4/C材料及其碳含量优化

采用Li_2CO_3与Li OH·H_2O为复合锂源制备LiFePO_4/C材料,同时优化了材料中的碳含量。由于氢氧化锂的熔点低于碳酸锂,在同样的烧结温度下,采用复合锂源可以获得更佳的熔融状态,在高温合成过程中使锂离子具有更高的扩散性,能够更顺利地得到高纯度的LiFePO_4晶相。通过优化碳包覆量达到提高导电性与控制晶粒尺寸的目的,使材料晶相结构完整,纯度高,表现出优秀的加工性能与电化学性能。所制得的LiFePO_4/C材料放电克容量达到158.2 m Ah·g~(-1),在全电池中经过100 d存储后容量保持率仍然高于94.0%,具有优异的长期可靠性。     

Selective water sorbents for multiple applications, 3. CaCl2 solution confined in micro- and mesoporous silica gels: Pore size effect on the “solidification-melting” diagram

In this communication we present a low-temperature “solidification-melting” phase diagram for CaCl₂/H₂O solutions confined in KSK and KSM silica gels. At salt concentrations of 0–48 wt. %, the diagram has been found to lie below the diagram reported for the bulk system by 15–30°C. It shows a depression of the solution melting point due to its confinment to the pores. Several other peculiarities of melting and solidification in this system are also reported and discussed. Beside fundamental interest, the data obtained could be of importance in many commercial areas such as refrigeration, accumulation of low temperature heat, frost prevention in building materials,etc.     

Simultaneous thermoanalytical investigations of (C6H5)4AsCl and (C6H5)4PCl under air and argon atmospheres

The thermoanalytical curves of (C₆H₅)₄AsCl (I) and (C₆H₅)₄PCl (II) were generated simultaneously by using a Netzsch simultaneous thermal analyser 409 under static air and dynamic argon atmospheres. The ranges of thermal stability of I and II were found to be 145–310°C and 137–365°C, respectively, and their melting points to be 261 and 278°C. The DTA profiles of I and II differ and can be used for their distinction.     

Synthesis, structure characterization and optical properties of a new tripotassium cadmium pentaborate, K3CdB5O10

A new ternary borate oxide, K₃CdB₅O₁₀, has been synthesized by solid-state reaction at 580 °C. The compound crystallizes in the monoclinic space group P2₁/n with a=7.6707 (7) Å, b=19.1765 (17) Å, c=7.8784 (6) Å, β=115.6083 (49)°, and Z=4. The crystal structure consists of a two-dimensional infinite [CdB₅O₁₀] layer, which forms by connecting isolated double ring [B₅O₁₀] groups and CdO₄ tetrahedra. K atoms filling in the interlayer and intralayer link the layers together and balance charge. The IR spectrum has been studied and confirmed the presence of both BO₃ and BO₄ groups, and the UV-vis-IR diffuse reflectance spectrum exhibits a band gap of about 3.4 eV. The DSC analysis proves that K₃CdB₅O₁₀ is a congruent melting compound.     

Synthesis, structure and magnetic properties of new phosphates K2Mn0.5Ti1.5(PO4)3 and K2Co0.5Ti1.5(PO4)3 with the langbeinite structure

New complex phosphates of the general formula K₂M_0.5Ti_1.5(PO₄)₃ (M=Mn, Co) have been obtained from the melting mixture of KPO₃, K₄P₂O₇, TiO₂ and CoCO₃·mCo(OH)₂ or Mn(H₂PO₄)₂ by means of a flux technique. The synthesized phosphates have been characterized by the single-crystal X-ray diffraction and the FTIR-spectroscopy. The compounds crystallize in the cubic system with the space group P2₁3 and cell parameters a=9.9030(14) Å for K₂Mn_0.5Ti_1.5(PO₄)₃ and a=9.8445(12) Å for K₂Co_0.5Ti_1.5(PO₄)₃. Both phosphates are isostructural with the langbeinite mineral and contain four formula unit K₂M_0.5Ti_1.5(PO₄)₃ per unit cell. The structure can be described using [M₂(PO₄)₃] framework composed of two [MO₆] octahedra interlinked via three [PO₄] tetrahedra. The Curie-Weiss-type behavior is observed in the magnetic susceptibility.     

Synthesis and Properties of Solid Solutions in The FeVMoO7–CrVMoO7 System

X-ray phase analysis (XRD), differential thermal analysis (DTA) and IR spectroscopy have shown that continuous substitution solid solutionsin are formed in the FeVMoO₇–CrVMoO₇ system. With increasing the degree of Cr³⁺ ion incorporation into the FeVMoO₇ structure, a crystal lattice contraction of the Fe_1–xCrxVMoO₇ solid solution arise. Elevation of temperature of its incongruent melting and gradual shifting of the corresponding IR absorption bands towards higher wavenumbers have been noticed, as well. The solid product of incongruent melting for x≤0.5 is the Fe_4–yCr_yV₂ Mo₃ O₂₀ solid solutions phase, whereas for x>0.5 Fe_2–zCr_z(MoO₄)₃ and Fe_2–u Cr_u O₃ solid solutions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Near infrared study of aqueous rare-earth ethylsulfates

The near infrared spectra of aqueous solutions of the ethylsulfates of La, Nd, Gd, Tb, Er, Yb, Lu, Y, and Na have been determined from about 0.2 mol-dm^–3 to nearly saturation. The extinction coefficients of water have been calculated taking into account the absorption of ethylslfate anions determined in separate experiments. Their values appeared to be nearly the same as that of pure water. The relative contents of free OH groups in 0.5 and 0.7M solutions have been estimated from the absorbances at 1160 nm. They were lower in solutions of the heavy rare-earth ethylsulfates (Tb, Er, Yb, Lu) than in equimolar solutions of the lighter ones (La, Nd), confirming our previous view that secondary hydration of the heavy trivalent rare-earth cations is distinctly stronger than that of the lighter ones. A comparison of the spectra of these aqueous ethylsulfates with those of perchlorates shows that the structure-breaking ability of the C₂H₅SO ₄ ^– ion is much smaller than that of perchlorate anion.     

Thermosonimetry and thermomicroscopy of the decomposition of NaClO4 and KClO4

Thermal decompositions of NaClO₄ and KClO₄ were followed by simultaneous TS-DTA and thermomicroscopy. For NaClO₄ TS curves corresponding to melting/decomposition and solidification of molten NaCl were found to consist of six peaks. During decomposition of KClO₄, three TS peaks appeared. The origin of these TS peaks is discussed on the basis of thermomicroscopic observations during which melting of the particles, evolution of bubbles of different sizes, formation of solid products of varied morphologies, vigorous vibration of these solids, and precipitation of NaCl or KCl were observed.     

Thermal stability and crystal structure of β-Ba3YB3O9

A new compound, β-Ba₃YB₃O₉, has been attained through solid phase transition from α-Ba₃YB₃O₉ at high temperatures. Differential thermal analysis (DTA) revealed the phase transition at about 1120°C, the melting temperature at about 1253°C. Its crystal structure has been determined from powder X-ray diffraction data. The refinement was carried out using the Rietveld method and the final refinement converged with R_p=10.5% and R_wp=13.7%. This compound belongs to the hexagonal space group R-3, with lattice parameters a=13.0441(1) Å and c=9.5291(1) Å. There are 6 formulas per unit cell and 7 atoms in the asymmetric unit. The structure of β-Ba₃YB₃O₉ is built up from Ba(Y)O₈, BaO₆ and YB₆O₁₈ units formed by one YO₆ octahedron and six BO₃ triangles with shared O atoms.     

Vibrational frequencies and force constants of N2O4 in complexes with molecules of different solvents determined by Raman spectra andAb initio calculation

The Raman spectra of N₂O₄ solutions in organic solvents have been recorded. The frequencies ofv ₁,v ₂, andv ₃ bands of N₂O₄ increase with increasing solvent electron-donor properties. Especially large changes ofv ₃ N-N stretching band have been observed (254.5 cm^–1 in n-hexane, 276.5 cm^–1 in 1,4-dioxane). The ab initio calculations have shown that the interaction between N₂O₄ and electron-donor molecules causes an increase of N-N and N-O stretching and O-N-O bending force constants of N₂O₄ in agreement with the results of Raman study.     

Interactions of Ba2YCu3O6+y with the Gd3NbO7 buffer layer in coated conductors

A systematic study of the chemical interaction of Ba₂YCu₃O_6+y and Gd₃NbO₇ was conducted under two processing conditions: purified air (21% p_o2), and 100 Pa p_o2 (0.1% p_o2). Phases present along the pseudo-binary join Ba₂YCu₃O_6z and Gd₃NbO₇ were found to be in two five-phase volumes within the system. Three common phases that are present in all samples are (Y,Gd)₂Cu₂O₅, Ba(Y,Gd)₂CuO₅ and Cu₂O or CuO (depending on the processing conditions). The assemblies of phases can be categorized in three regions, with Ba₂YCu₃O_6+y: Gd₃NbO₇ ratios of (I)<5.5:4.5; (II)=5.5:4.5; and (III)>5.5:4.5. The lowest melting temperature of the system was determined to be ≈938 °C in air, and 850 °C at 100 Pa p_o2. Structure determinations of two selected phases, Ba₂(Gd_xY_1−x)NbO₆ (Fm3¯m, No. 225), and (Gd_xY_3−x)NbO₇ (C222₁, No. 20 and Ccmm, No. 63), were completed using the X-ray Rietveld refinement technique. Reference X-ray powder diffraction patterns for selected phases of Ba₂(Gd_xY_1−x)NbO₆ (x=0.2, 0.4, 0.6, and 0.8) and (Gd_xY_3−x)NbO₇ (x=0.6, 1.2, 1.8, 2.4 and 3) have been prepared for inclusion in the Powder Diffraction File (PDF).