Kalorimetrischer und elektronenmikroskopischer Nachweis von Entmischungserscheinungen im pseudobinären System Dipalmitoyllecithin/ Dipalmitoyl-N-methyl-kephalin

By means of differential scanning calorimetry and electron microscopy the miscibility properties of the system dipalmitoyllecithin/dipalmitoyl-N-methyl-cephaline/ water (50 wt-% water) was studied. In theL _α-phase (high temperature phase) both phospholipids were completely miscible. On the other hand in the low temperature phases demixing occurs in the concentration range fromx _MPE?0.05 tox _MPE?0.35. The electron microscopy confirms these results. The electron microscopic pictures showed the ripple structure of theP _β phase.     

Deuterium diffusion in vanadium deuterides (VDx; 0.4?x?0.6) studied by H NMR

Sites and dynamics of deuterium in VD_0.50 as well as in VD_0.40 and VD_0.57 have been studied by means of X-ray diffraction, differential scanning calorimetry and ²H NMR. VD_0.40 consists of the body-centered-cubic (bcc) α_D and body-centered-tetragonal (bct) β_D phases at room temperature and only the octahedral (O) sites are occupied in the β_D phase. On the other hand, in VD_0.50, consisting of the bctβ_D phase at room temperature, the O site is dominantly occupied with a small occupancy of the tetrahedral (T) sites in the β_D phase. VD_0.57 is composed of the bccα′_D (a high-deuterium-concentration phase of the α_D phase) and bctβ_D phases at room temperature, and the occupancy of the T sites is observed. The mean activation energy (E_D) of the deuterium diffusion is much larger for the O sites than for the T sites, and the diffusion is also much slower in the O sites. The mean E_D values for the O sites are almost the same in the β_D phase of VD_0.40 and VD_0.50, although the distribution of the mean residence time is much larger in VD_0.50 than in VD_0.40.     

Phase formation of BICUVOX solid solutions

Phase formation of Bi₄(V_{1 ? x} Cu _x )₂O_{11 ? z} solid solutions (BICUVOX) with x = 0.00–0.20 and Δx = 0.02 was studied. The concentration stability ranges were determined for the α, β, and γ polymorphs of BICUVOX solid solutions at room temperature, and their unit cell parameters were revised. The following was found to occur as x rises: the α ai β phase transition temperature between the monoclinic and orthorhombic phases shifts down, the β ai γ phase transition temperature to the high-temperature tetragonal phase shifts down, and the order-disorder phase transition temperature between γ′ ai γ tetragonal phases shifts up.     

Structural characterization of the Ta-rich part of the Ta-Al system

The Ta-rich part of the Ta-Al system has been investigated. On the one hand, the accommodation of the non-stoichiometry in the σ phase has been studied by Rietveld refinement of X-ray powder data obtained from different samples on both sides of the ideal composition (Ta₂Al, P4₂/mnm, tP30). On the other hand, the structure of the β phase has been determined ab initio from powder synchrotron data (analyzed composition Ta_50.7Al_49.3, refined composition Ta_52.6(5)Al_47.4(5) (Ta_45.2(4)Al_40.8(4)), stoichiometric composition Ta₄₈Al₃₈, mP86, P2₁/c, a=9.8707(1) Å, b=9.8766(1) Å, c=16.3539(2), β=116.478(1), R_B=2.6%). This phase is shown to be closely related to the group of the topologically close packed phases. In addition, phase relations have been accurately determined in the Ta-rich end of the system.     

Synthesis, Structures, and Thermal Expansion of the La2W2−xMoxO9 Series

The La₂W_2−xMo_xO₉ series has been synthesized by the ceramic method. An alternative synthesis using microwave radiation is also reported. La₂W₂O₉ has two polymorphs and the low-temperature phase (α) transforms to the high-temperature form (β) at 1077°C. The influence of the W/Mo substitution in this phase transition has been investigated by DTA. The β structure for x≥0.7 compositions can be prepared as single phase at any cooling rate. The β phase for 0.3≤x≤0.7 compounds can be prepared as single phase by quenching, whereas a mixture of α and β phases is obtained by slow cooling. The W/Mo ratio in both coexisting phases is different with the β-phase having a higher Mo content. The x=0.1 and 0.2 compounds have been prepared as mixtures of phases. The room temperature structure of β-La₂W_1.7Mo_0.3O₉ has been analyzed by the Rietveld method in P2₁3 space group. The final R-factors were R_WP=9.0% and R_F=5.6% with a structure similar to that of β-La₂Mo₂O₉. Finally, the thermal expansion of both types of structures has been determined from a thermodiffractometric study. The thermal expansion coefficients were 2.9×10⁻⁶ and 9.7×10⁻⁶°C⁻¹ for α-La₂W₂O₉ and β-La₂W_1.2Mo_0.8O₉, respectively.     

Temperature and concentration dependent electrical resistivity of Ho1−xTixCo2–hydrogen system

The structure and electrical resistivity of Ho_1−xTi_xCo₂–hydrides (x = 0.1–0.6) have been determined through the powder X-ray diffraction (XRD) and temperature dependence of electrical resistivity (ρ(T)) at different hydrogen concentrations. The variations in the lattice parameters in different phase regions and the lattice expansion with respect to the hydrogen concentration have been studied. The temperature dependent electrical resistivity of hydrides has been discussed based on the conduction electron scattering and spin fluctuation scattering mechanisms. The changes in ρ(T) upon Ti substitution and increasing concentration of hydrogen have been discussed and the results have been correlated with their structural properties.     

The system copper-tellurium

The system copper-tellurium was investigated by DTA, DSC, and X-ray methods. A phase diagram with the phases Cu_2?xTe (33.5–36.2 mole% Te), Cu_3?xTe₂ (40–41 mole%), and CuTe was constructed. In the homogeneity ranges of the nonstoichiometric phases several superstructures were observed. The lattice parameters and d values of some of these phases are given.     

Etude des phases du système FeVO4VO2, obtenues par synthèse hydrothermale à 70 kbar et 1000°C

The solid solutions, Fe³⁺_xV⁵⁺_xV⁴⁺_2(1?x)O₄, have been synthesized at 70 kbar and 1000°C under hydrothermal conditions. Their structure is rutile-type when x < 0.66, whereas it is α-PbO₂-type when x > 0.66. In the latter zone, four different phases have been obtained. For x > 0.9, these compounds have an orthorhombic symmetry (O) if the cations are disordered, while the symmetry lowers to monoclinic (Mβ) if the cations are ordered. When 0.66 < x < 0.75) only one monoclinic phase (Mγ) has been obtained. The transition from Mβ to Mγ or from O to Mγ occurs through a triclinic phase T which is stable for 0.75 < x < 0.9. A single-crystal structural refinement of this phase has been carried out and seems to indicate that this phase is also disordered.     

Interstitial superstructures in the TaD system

Ordered deuterium arrangements and order-disorder transformations of the tantalum deuterides in the range TaD_0.50TaD_0.78 have been studied by neutron diffraction and calorimetry at temperatures between ?170 and 120°C. In addition to the disordered phase (α), three ordered phases based on the superstructures Ta₂D_1+x (β₁), Ta₄D₃, (γ), and TaD (δ) are clarified. The Ta₂D_1+x structure is a nonstoichiometric from of the Ta₂D superstructure over the rangex < 0.5. The γ-phase is formed below ?70°C near Ta₄D₃, and transforms into theβ₁and δ-phases, respectively, in the hypo and hyperstoichiometric compositions. The δ-phase that exists beyond TaD_0.75 changes to the disordered α-phase around 100°C.     

Preparation,structure, and charge transport characteristics of BIFEVOX ultrafine powders

Existence boundaries, structure, and transport parameters of ultrafine powders were studied in Bi₄V_{2 ? x} Fe _x O_{11 ? x} (BIFEVOX) solid solutions. The details of synthesis of the solid solutions via liquid precursors are analyzed comparatively. In general, BIFEVOX formation via liquid precursors is similar to phase formation in solid-phase synthesis. With low iron levels (x = 0.05–0.1), solid solutions are formed in the monoclinic α phase (space group C2/m) The compositions with x = 0.125 and 0.15 are mixtures of α- and β phases. In the range 0.2 < x < 0.7, the Bi₄V_{2 ? x} Fe _x O_{11 ? x} solid solution has the structure of the γ phase of Bi₄V₂O₁₁ (space group I4/mmm). The β phase in the system in question has a very narrow existence range in the vicinity of x = 0.175. The average particle sizes of the powders prepared by various methods are within 0.5–3 μm. In the powders prepared via liquid precursors, however, the distribution peak shifts toward smaller sizes, to 0.3–1 μm. Mechanical activation conserves the structure of the γ phase of BIFEVOX, and unit cell parameters change only insignificantly; however, the crystal lattice is slightly distorted. The electrical conductivity of BIFEVOX was studied as a function of temperature, preparation technology, and composition using impedance spectroscopy. Equivalent circuits of cells were analyzed. The conductivity of samples prepared by solution technology is always higher than for samples prepared by the solid-phase process. Features of electrical conductivity versus temperature for various phases are noted. All transitions on the conductivity curves match the features of linear thermal expansion curves. Compositions with doping levels x= 0.1–0.3 have the highest total conductivities.     

Crystal structure of Mg0.65Sc0.35Dx deuterides studied by X-ray and neutron powder diffraction

The structural properties of the Mg_0.65Sc_0.35D_x deuterides have been investigated by X-ray and neutron powder diffraction at different deuterium content (0?x?2.2 D/f.u.). The metallic phase adopts a pseudo-CsCl structure (Pm-3m space group (SG); a=3.5921(2) Å) that transforms upon hydrogenation into a face centered cubic (FCC) phase involving an elongation of the c-axis, a shrinkage of the a-axis and a re-ordering of the metallic atoms. The fully hydrided compound (2.2 D/f.u.) adopts a cubic structure (Fm-3m SG; a=4.8087(7) Å) and deuterium is located in fully occupied tetrahedral sites and partially filled (24%) octahedral sites. Upon desorption, a two-phase domain appears with coexistence of a hydrogen-rich (1.55 D/f.u.) and a hydrogen-poor (0.85 D/f.u.) phase (Fm-3m SG; a=4.7598(3) and 4.6936(3) Å, respectively). All deuterium atoms are located in the tetrahedral sites with different occupancy factors: 77% for the H-rich phase and 43% for the H-poor phase. The appearance of a plateau in the pressure-composition-isotherm curve measured at 573 K confirms this two-phase behavior. The structural properties of the Mg_0.65Sc_0.35D_x system are discussed and compared with other body centered cubic (BCC) alloys adopting the same structure.     

Subsolidus phase relations in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Li<Subscript>2</Subscript>O-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> (Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>) systems

The phase composition has been studied and an equilibrium phase diagram has been designed for the Al₂O₃-Li₂O-R₂O₅ (R = Ta or Nb) systems in the subsolidus region up to 1000°C and 85 mol % Li₂O. New phases with the composition Li_1+x Al_1?x O_2?x , where x = 0–0.67, have been found.     

Glass-ceramic nanocomposites in the [(1 − x)PbO–xBaO]–Na2O–Nb2O5–SiO2 system: Crystallization and dielectric performance

The crystallization process, microstructure and dielectric properties of [(1 − x)PbO–xBaO]–Na₂O–Nb₂O₅–SiO₂ (PBNNS) (0 ≤ x ≤ 1) glass-ceramics prepared by controlled crystallization were investigated. The crystallization strategies for acquiring nano-crystallized PBNNS glass-ceramics were monitored by differential thermal analysis (DTA). X-ray diffraction (XRD) analysis revealed a major crystal phase transition in PBNNS glass matrix as the crystallization temperature increased. At low temperatures (700–750 °C), the major crystal phases precipitating in the glass matrix are identified as Pb₂Nb₂O₇ for x = 0, Ba₂NaNb₅O₁₅ for x = 1 and their solid solution for 0.2 ≤ x ≤ 0.8; while at higher temperatures (≥850 °C), heat treatment produces different crystalline phases, PbNb₂O₆ and NaNbO₃ for x = 0, Ba₂NaNb₅O₁₅ and NaNbO₃ for x = 1, and the solid solution of these three phases for 0.2 ≤ x ≤ 0.8. Corresponding to the result of phase transition, microstructural observation proves increasing crystallite sizes with increasing temperature of heat treatment. At different crystallization temperatures, the dielectric properties of the [(1 − x)PbO–xBaO]–Na₂O–Nb₂O₅–SiO₂ glass-ceramics show a strong dependence on the chemical composition x. At low temperatures (700–750 °C), a maximum of the dielectric constant of the PBNNS glass-ceramic is found for the composition x = 0.6; while at higher crystallization temperatures (≥850 °C), the dielectric constants of all samples (0 ≤ x ≤ 1) exhibit decreasing values with increasing x.     

Phase behaviors of Gemini cationic surfactants/n-butanol/water systems

Phase diagrams for ternary system of the Gemini cationic surfactants, N,N-long chain alkyl-2-hydroxyl-N,N,N,N-tetramethyl diammonium dichloride (G_nCl₂) with butanol and water have been drawn based on experimental data at 25 °C. The phase diagrams show that L phase and different liquid crystalline phases are existent in the ternary system at different components. Electric conductivity of the L phase has been studied. Small-angle X-ray scattering (SAXS), ²H (deuterium) quadrupolar splitting (²H NMR) and the polarizing-light microscope were employed to confirm the characteristic texture structures and the microstructure of three different liquid crystalline phases.     

Magnetic properties of iron-intercalated titanium diselenide

Powder samples of Fe_xTiSe₂ (0.00 ≤ x ≤ 0.50) have been prepared by direct reaction of high purity elements. Crystal parameters were determined by the Debye-Scherrer powder diffraction technique. Magnetic susceptibility measurements were made by the Faraday method in the temperature range 1.5–300 K and indicated magnetic odering for compositions with x > 0.03. The magnetic ordering temperature, T_m, was observed to move to higher temperature with increasing iron concentration. These results have been interpreted in terms of a spin-glass model for low iron concentrations (x < 0.2) and antiferromagnetism for high concentrations (x > 0.2).     

Determination of the deuterium/hydrogen ratio in gas reaction products by laser-induced breakdown spectroscopy

This paper reports the first application of laser-induced breakdown spectroscopy technique (LIBS) to the determination of deuterium/hydrogen numeric ratio (β) in the headspace gases, essentially HD + H₂, that are generated by the hydrolysis of NaBD₄–NaBH₄ mixtures (molar fraction of NaBD₄, x = 50–100%) in acidic H₂O media (0 < pH < 1). The LIBS measurement of β can be easily achieved with a coefficient of variation better than 5% (over four replicates). The value of β allowed the calculation of the molar fraction of NaBD₄, x_LIBS, with a coefficient of variation better than 2.5%. The comparison of x vs. x_LIBS gives results that are in good agreement, within an average deviation of 3%, for x in the range of 50–100%. The best performances are obtained for β close to unit, which makes LIBS perfectly suited for the detection of H–D exchange taking place during aqueous hydrolysis of NaBD₄ or NaBH₄.     

Structural, microstructural and surface properties of a specific CeO2-Bi2O3 multiphase system obtained at 600 °C

Polycrystalline samples of (1−x) CeO₂−x/2 Bi₂O₃ phases, where x is the atom fraction of bismuth have been synthesized by the precipitation process and after the thermal treatment at 600 °C, under air. Samples are first characterized by the X-ray diffraction and scanning electron microscopy. To determine the samples specific surface areas, Brunauer-Emmett-Teller (BET) analyses have been performed. In the composition range 0≤x≤0.20, a cubic solid solution with fluorite structure is obtained. For compositions x comprised between 0.30 and 0.90, two types of T′ (or β′) and T (or β) tetragonal phases, similar to the well-known β′ or β Bi₂O₃ metastable structural varieties, are observed. However, the crystal cell volumes of these β′ or β Bi₂O₃ phases increase with the composition x in bismuth: this might be due to the presence of defects or substitution by cerium atoms, in the tetragonal lattices. Using X-ray diffraction profile analyses, correlations between bismuth composition x and crystal sizes or lattice distortions have been established. The solid-gas interactions between these polycrystalline materials and air-CH₄ and air-CO flows have been studied as a function of temperature and composition x, using Fourier transform infrared (FTIR) analyses of the conversions of CH₄ and CO gases into the CO₂ gas. The transformations of CH₄ and CO molecules as a function of time and temperature are determined through the intensities of FTIR CO₂ absorption bands. Using the specific surface areas determined from BET analyses, these FTIR intensities have been normalized and compared. For all bismuth compositions, a low catalytic reactivity is observed with air-CH₄ gas flows, while, for the highest bismuth compositions, a high catalytic reactivity is observed with air-CO gas flows.     

The phase diagram of KNO3-KClO3

The binary phase diagram of KNO₃-KClO₃ is studied by means of differential scanning calorimetry (DSC) and high-temperature X-ray diffraction. The limited solid solutions, K(NO₃)_1−x(ClO₃)_x (0<x<0.20) and K(NO₃)_1−x(ClO₃)_x (0.90<x<1.0), were formed in the KNO₃-based solid solutions and KClO₃-based solid solutions phase, respectively. For KNO₃-based solid solutions, KNO₃ ferroelectric phase can be stable from 423 to 223 K as a result of substituting of NO₃ by ClO₃-radicals. The temperatures for solidus and liquidus have been determined based on limited solid solutions. Two models, Henrian solution and regular solution theory for KNO₃-based (α) phase and KClO₃-based (β) phase, respectively, are employed to reproduce solidus and liquidus of the phase diagram. The results are in good agreement with the DSC data. The thermodynamic properties for α and β solid solutions have been derived from an optimization procedure using the experimental data. The calculated phase diagram and optimized thermodynamic parameters are thermodynamically self-consistent.     

Liquid phase separation of ternary Al–In–Sn/Ge monotectic type alloys investigated with calorimetric method

The phase equilibrium, thermodynamic properties and liquid demixing patterns for binary Al_100−xIn_x, ternary (Al_100−xIn_x)₉₀Sn₁₀ and (Al_100−xIn_x)₉₀Ge₁₀ (x = wt.%) alloys are investigated by differential scanning calorimetry (DSC) method. The corresponding phase diagrams are experimentally established, and it is found that both monotectic temperature and critical temperature for immiscibility gap decrease when either Sn or Ge is added to binary Al_100−xIn_x alloys. The enthalpy of fusion for binary Al–In alloys, ternary Al–In–Sn and Al–In–Ge alloys shows linear functions with In content, and the introduction of Sn and Ge elements decreases the enthalpy of fusion. The liquid phase separation mechanism is discussed in relation to the DSC curves and solidified microstructures. It is demonstrated that the core and shell phases can be altered by the addition of Ge element in (Al_100−xIn_x)₉₀Ge₁₀ alloys as compared with those in binary Al_100−xIn_x and ternary (Al_100−xIn_x)₉₀Sn₁₀ alloys. This provides an effective way to switch the inner and outer phases for core–shell structure.     

Structure,microstructure and microhardness of rapidly solidified Smy(FexNi1-x)4Sb12 (x = 0.45, 0.50, 0.70, 1) thermoelectric compounds

Skutterudites are interesting compounds for thermoelectric applications. The main drawback in the synthesis of skutterudites by solidification of the melt is the occurrence of two peritectic reactions requiring long annealing times to form a single phase. Aim of this work is to investigate an alternative route for synthesis, based on rapid solidification by planar flow casting. The effect of cooling rate on phases formation and composition, as well as on structure, microstructure and mechanical properties of the filled Sm_y(Fe_xNi_1-x)₄Sb₁₂ (x = 0.45, 0.50, 0.70, 1) skutterudites was studied. Conversely to slowly cooled ingots, rapidly quenched ribbons show skutterudite as the main phase, suggesting that deep undercooling of the liquid prevents the nucleation of high temperature phases, such as (Fe,Ni)Sb and (Fe,Ni)Sb₂. In as-quenched samples, a slightly out of equilibrium Sm content is revealed, which does not alter the position of the p/n boundary; nevertheless, it exerts an influence on crystallographic properties, such as the cell parameter and the shape of the Sb₄ rings in the structure. As-quenched ribbons show a fine microstructure of the skutterudite phase (grain size of 2–20 μm), which only moderately coarsens after annealing at 873 K for 4 days. Vickers microhardness values (350–400 HV) of the skutterudite phase in as-quenched ribbons are affected by the presence of softer phases (i.e. Sb), which are homogeneously and finely dispersed within the sample. The skutterudite hardens after annealing as a consequence of a moderate grain growth, which limits the matrix effect due to the presence of additional phases.