Phase transitions of CaTiO3 ceramics sintered with the aid of NaF and MgF2

New phases with initial composition (1 ? x)CaTiO₃ ? xNaF ? xMgF₂ (0 ≤ x ≤ 0.20) have been prepared at low temperature (950 °C) from mixtures of CaTiO₃ and fluorides NaF and MgF₂. The oxyfluorides obtained have been characterized by X-ray diffraction at room temperature and indexed by isotypy with orthorhombic CaTiO₃. The microstructures of these phases are observed by scanning electron microscopy. Dielectric measurements have been carried out during cooling cycle from 500 °C to room temperature at two frequencies (100 Hz, 1 kHz). Differential scanning calorimetry (DSC), thermogravimetry (TG) and differential thermogravimetry (DTG) analyses have been performed, respectively, from room temperature up to 550 °C (DSC) and 920 °C (TG–DTG). The dielectric measurements revealed two anomalies which have been confirmed by DSC analyses. These phenomena are ascribed to second order phase transitions. The variation of the real permittivity with temperature is in agreement with the class I capacitor specifications. However, the dielectric losses have to be improved.     

Isobaric specific heat capacity of {xCH3OH + (1 − x)H2O} with x = (1.0000, 0.7943, 0.4949, 0.2606, 0.1936, 0.1010, and 0.0496) at T = (280, 320, and 360) K in the pressure range from (0.1 to 15) MPa

Measurements of the isobaric specific heat capacities for {xCH₃OH + (1 − x)H₂O} with x = (1.0000, 0.7943, 0.4949, 0.2606, 0.1936, 0.1010, and 0.0496) were carried out by the calorimeter with the thermal relaxation method, which we have developed, at T = (280, 320, and 360) K in the pressure range from (0.1 to 15) MPa. The present c_p measurements for (methanol + water) show mole fraction dependence at constant temperature with the maximum, and the maximum shifts to greater values of mole fraction with increasing temperature. Pressure dependence of the present measurements is insignificant. Temperature dependence increases with increasing mole fraction.     

XAFS characterization of La1−xSrxMnO3±δ catalysts prepared by Pechini’s method

XAFS experiments at the Mn and Sr K-edges were carried out in order to investigate the short-range arrangement of Mn and Sr sites on La_1−xSr_xMnO_3±δ highly doped perovskites (x = 0, 0.2, 0.4 and 0.6). The Mn K-edge EXAFS spectra show a static Jahn–Teller distortion of the MnO₆ for x = 0 and 0.2, which is drastically reduced as x increases. The distortion of perovskite, characterized by the Mn–O–Mn tilt angle, progressively decreases with increasing Sr contents. Sr K-edge results indicated a decrease on the Sr–Mn coordination number upon Sr doping. Based on this and TPD results, a charge compensating mechanism is proposed suggesting a partial Mn oxidation and formation of Mn defect vacancies due to the introduction of Sr.     

Contribution to study of the thermodynamics properties of mixtures containing 2-methoxy-2-methylpropane,alkanol, alkane

Excess molar enthalpies for the ternary system {x₁ 2-methoxy-2-methylpropane (MTBE) + x₂ 1-pentanol + (1 − x₁ − x₂) hexane} and the involved binary mixture {x 1-pentanol + (1 − x) hexane}, have been measured at T = 298.15 K and atmospheric pressure over the whole composition range. We are not aware of the existence of previous experimental measurement of the excess enthalpy for the ternary mixture under study in the literature currently available. Values of the excess molar enthalpies were measured using a Calvet microcalorimeter. The results were fitted by means of different variable degree polynomials. The ternary contribution to the excess enthalpy was correlated with the equation due to Verdes et al. (2004), and the equation proposed by Myers–Scott (1963) was used to fit the experimental binary mixture measured in this work. Smooth representations of the results are presented and used to construct constant excess molar enthalpy contours on Roozeboom diagrams. The excess molar enthalpies for the binary and ternary system are positive over the whole range of composition. The binary mixture {x 1-pentanol + (1 − x) hexane} is asymmetric, with its maximum displace toward a high mole fraction of decane. The ternary contribution is also positive with the exception of a range located around the rich compositions of 1-pentanol, and the representation is asymmetric.Additionally, the group contribution model of the UNIFAC model, in the versions of Larsen et al. (1987) [18] and Gmehling et al. (1993) [19] was used to estimate values of binary and ternary excess enthalpy. The experimental results were used to test the predictive capability of several empirical expressions for estimating ternary properties from binary results.     

Thermochemical behavior of crown ethers in the mixtures of water with organic solvents. Part VIII. Hydrophobic hydration and preferential solvation of 1,4-dioxane in {(1 − x)amide + xH2O} at T = 298.15 K

The enthalpies of solution of 1,4-dioxane in {(1 − x)F + xH₂O}, {(1 − x)NMF + xH₂O}, and {(1 − x)DMF + xH₂O} have been measured within the whole mole fraction range at T = 298.15 K. Based on the obtained data, the effect of substituting methyl groups at the nitrogen atom in formamide on the preferential solvation of 1,4-dioxane has been analyzed. A simple model has been proposed to describe the influence of structural and energetic properties of the mixed solvent on the energetic effect of hydrophobic hydration and preferential solvation of 1,4-dioxane by the components of the examined mixture.     

Thermochemical behaviour of crown ethers in the mixtures of water with organic solvents. Part IX. Effect of base–acid properties of {(1 − x)AN + xH2O} on the solution enthalpy of cyclic ethers in this mixed solvent at T = 298.15 K

The enthalpies of solution of cyclic ethers: 1,4-dioxane, 12-crown-4 and 18-crown-6 in {(1 ? x)AN + xH₂O} have been measured over the whole mole fraction range at T = 298.15 K. Based on the results obtained, the effects of base–acid properties of mixed solvent and the number of –CH₂CH₂– groups in cyclic ethers molecules on the solution enthalpy of cyclic ethers in {(1 ? x)AN + xH₂O} have been analyzed.     

Substitution of Sr2+ by Eu3+ in Bi-2201 ceramics,effects on structure and physical properties

In this paper, we report the effects of the substitution of Sr by Eu on the properties of Bi-2201 ceramics. Samples with nominal compositions of Bi₂Sr_2?xEu_xCuO_y (x = 0–0.4) are elaborated in air by solid state reaction. They are characterized by means of X ray diffraction (XRD), scanning electron microscopy (SEM), magnetic and resistivity measurements. The undoped sample (x = 0) is monophasic and its structure belongs to phase A. No trace of superconductivity is observed down to 2 K for this sample and the variation of resistivity with temperature shows a semiconducting behaviour. As Eu is added and for x ≥ 0.2, the samples convert totally to B or Raveau phase and become superconducting. The highest T_c, obtained from both magnetic and resistivity measurements, is observed for x = 0.3. In the normal state, all the samples exhibit a semiconducting character which decreases as well as resistivity when the Eu content increases. The refinement of cell parameters is done with considering the structural modulation. The study shows that the substitution of Sr²⁺ by Eu³⁺ leads to an increase of a and b parameters, while c decreases similarly to those of the La doped phases. The a axis component of the modulation is observed to be independent of Eu content, while the c axis one increases slightly as this content increases. The XRD analysis has also revealed that the limit solubility of the used Eu₂O₃ oxide is situated between x = 0.3 and 0.4 of Eu content. The SEM micrographs show that the undoped sample consists of poorly connected grains with a random distribution. A quite different microstructure is obtained for the doped samples. The grains are more connected and have a flat shape which is characteristic of the Bi-based superconductors.     

Experimental excess molar properties of binary mixtures of (3-amino-1-propanol + isobutanol, 2-propanol) at T = (293.15 to 333.15) K and modelling the excess molar volume by Prigogine–Flory–Patterson theory

Density and viscosity of binary mixtures of (x₁3-amino-1-propanol + x₂isobutanol) and (x₁3-amino-1-propanol + x₂2-propanol) were measured over the entire composition range and from temperatures (293.15 to 333.15) K at ambient pressure. The excess molar volumes and viscosity deviations were calculated and correlated by the Redlich–Kister (RK) equation. The thermal expansion coefficient and its excess value, isothermal coefficient of excess molar enthalpy, and excess partial molar volumes were determined by using the experimental values of density and are described as a function of composition and temperature. The excess molar volumes are negative over the entire mole fraction range for both mixtures and increase with increasing temperature. The excess molar volumes obtained were correlated by the Prigogine–Flory–Patterson (PFP) model. The viscosity deviations of the binary mixtures are negative over the entire composition range and decrease with increasing temperature.     

Measurements of HmE and VmE for (propane + sulphurhexafluoride) in the near critical region

A flow mixing calorimeter followed by a vibrating-tube densimeter has been used to measure excess molar enthalpies H_m^E and excess molar volumesV_m^E of {xC₃H₈ +  (1  − x)SF₆}. Measurements over a range of mole fractionsx have been made at the pressure p =  4.30 MPa at eight temperatures in the rangeT =  314.56 K to 373.91 K, in the liquid region at p =  3.75 MPa andT =  314.56 K, in the two phase region at p =  3.91 MPa andT =  328.18 K, and in the supercritical region at p =  5.0 MPa andT =  373.95 K. The measurements are compared with results from the Patel–Teja equation of state which reproduces the main features of the excess function curves as well as it does for similar measurements on{xCO₂ +  (1  − x)C₂H₆} ,{xCO₂ +  (1  − x)C₂H₄} and{xCO₂ +  (1  − x)SF₆} reported previously.     

Microstructures and electrochemical hydrogen storage properties of novel Mg–Al–Ni amorphous composites

The amorphous Mg–Al–Ni composites were prepared by mechanical ball-milling of Mg₁₇Al₁₂ with x wt.% Ni (x = 0, 50, 100, 150, 200). The effects of Ni addition and ball-milling parameters on the electrochemical hydrogen storage properties and microstructures of the prepared composites have been investigated systematically. For the Mg₁₇Al₁₂ ball-milled without Ni powder, its particle size decreases but the crystal structure does not change even the ball-milling time extending to 120 h, and its discharge capacity is less than 15 mAh g^?1. The Ni addition is advantageous for the formation of Mg–Al–Ni amorphous structure and for the improvement of the electrochemical characteristics of the composites. With the Ni content x increasing, the composites exhibit higher degree of amorphorization. Moreover, the discharge capacity of the composite increases from 41.3 mAh g^?1 (x = 50) to 658.2 mAh g^?1 (x = 200) gradually, and the exchange current density I₀ increases from 67.1 mA g^?1 (x = 50) to 263.8 mA g^?1 (x = 200), which is consistent with the variation of high-rate dischargeability (HRD). The ball-milled Mg₁₇Al₁₂ + 200 wt.% Ni composite has the highest cycling discharge capacity in the first 50 cycles.     

Near critical measurements of HmEandVmE for { xCO2 + (1 − x)SF6} and measurements made over the pressure range 2.5 to 10.0 MPa at the temperature T = 301.95 K

A flow mixing calorimeter, followed by a vibrating tube densimeter, has been used to measure excess molar enthalpies H_m^Eand excess molar volumesV_m^E of {xCO₂ +  (1  − x)SF₆}. Measurements over a range of mole fraction x have been made at the temperatures T =  302.15 K and T =  305.65 K at the pressures (3.76, 5.20, 6.20, and 7.38) MPa. The lowest pressure 3.76 MPa is close to thecritical pressure of SF₆ and the highest pressure 7.38 MPa is close to the critical pressure of CO ₂. Measurements atx =  0.5 have been made over the pressure range (2.5 to 10.0) MPa at the temperature 301.95 K. Some of the measurements are very close to the critical locus of the mixture. The measurements are compared with the Patel–Teja equation of state which reproduces the main features of the excess function curves as well as it does for similar measurements on {xCO₂ +  (1  − x)C₂H₆} and{xCO₂ +  (1  − x)C₂H₄} . The equation was used to calculate residual enthalpies and residual volumes for the pure components and for the mixture, and inspection of the way these combine to give excess enthalpies and volumes assisted the interpretation of the pressure scan measurements.     

Near critical measurements of HmE andVmE for (ethane + sulphur hexafluoride)

A flow mixing calorimeter and a vibrating-tube densimeter have been used to measure excess molar enthalpies H_m^E and excess molar volumes V_m^E of {xC₂H₆ +  (1  − x)SF₆ }. Measurements over a range of mole fractions x have been made at T =  305.65 K and T =  312.15 K and at the pressures (3.76, 4.32, 4.88 and 6.0) MPa. The pressure 3.76 MPa is close to the critical pressure of SF₆, the pressure 4.88 MPa is close to the critical pressure of C₂H₆, and the pressure 4.32 MPa is midway between these values. The measurements are compared with the Patel–Teja equation of state which reproduces the main features of the excess function curves as well as it does for similar measurements on {xCO₂ +  (1  − x)C₂H₆ }, {xCO₂ +  (1  − x)C₂H₄ } and {xCO₂ +  (1  − x)SF₆ }.     

Comparison of the electrochemical properties of metallic layered nitrides containing cobalt,nickel and copper in the 1 V–0.02 V potential range

We report the first example of an intercalation compound based on the nitrogen framework in which lithium can be intercalated and deintercalated. A comparison of the structural and electrochemical properties of the ternary lithium cobalt, nickel and copper nitrides is performed. Vacancy layered structures of ternary lithium nitridocobaltates Li_3−2xCo_xN and nitridonickelates Li_3−2xNi_xN with 0.10 ⩽ x ⩽ 0.44 and 0.20 ⩽ x ⩽ 0.60, respectively, are proved to reversibly intercalate Li ions in the 1 V–0.02 V potential range. These host lattices can accommodate up to 0.35 Li ion par mole of nitride. Results herein obtained support Li insertion in vacancies located in Li₂N⁻ layers while interlayer divalent cobalt and nickel cations are reduced to monovalent species. No structural strain is induced by the insertion–extraction electrochemical reaction which explains the high stability of the capacity in both cases. For the Li_1.86Ni_0.57N compound, a stable faradaic yield of 0.30 F/mol, i.e. 130 mAh/g, is maintained at least for 100 cycles. Conversely, the ternary copper nitrides corresponding to the chemical composition Li_3−xCu_xN with 0.10 ⩽ x ⩽ 0.40 do not allow the insertion reaction to take place due to the presence of monovalent copper combined with the lack of vacancies to accommodate Li ions. In the latter case, the discharge of the lithium copper nitrides is not reversible.     

Hopping conductivity of distorted K2NiF4-type (Ca1+xNd1−x)CrO4

Orthorhombic distorted K₂NiF₄-type (Ca_1+xNd_1?x)CrO₄ (0.00 ≤ x ≤ 0.15) was synthesized using a standard ceramic technique. The cell parameters (a and c) decreased, whereas the cell parameter (b) increased with the increase in x. The variation in the global instability index (GII) indicated that the crystal stability of (Ca_1+xNd_1?x)CrO₄ was not influenced by the Cr⁴⁺ ion content. At all temperatures, the electrical conductivity (σ) of (Ca_1+xNd_1?x)CrO₄ increased with the increase in x. (Ca_1+xNd_1?x)CrO₄ was a p-type semiconductor and exhibited hopping conductivity in a small-polaron model in the temperature range of 290 K ≤ T ≤ 713 K. The Cr⁴⁺ ion acts as an acceptor, and the electron transfer through the Cr³⁺–O–Cr⁴⁺ path becomes active as a result of the Cr⁴⁺ ion content and the Cr–O(1) distance.     

Effects of NiO addition on the structure and electric properties of Dy3−xNixFe5O12 garnet ferrite

Polycrystalline garnet ferrites Dy_3?xNi_xFe₅O₁₂ with varying Ni substitutions (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) have been prepared by the standard ceramic technique and their crystalline structures were investigated by using X-ray diffraction and IR spectroscopy. The X-ray diffraction analysis showed that all samples have a single cubic garnet phase. The materials prepared are identified by infrared rays which indicate the presence of three absorption bands ν₂, ν₃ and ν₄ which represent the tetrahedral, octahedral and dodecahedral sites respectively which characterize the garnet ferrite.The dielectric constant (?), and dielectric loss (tan δ) of the prepared samples were measured at 1 kHz in the temperature range 300–700 K. The dielectric constant (?), and dielectric loss (tan δ) are functions of temperature.The initial magnetic permeability has been studied at different temperatures. The initial magnetic permeability (μ_i) increases gradually with increasing temperature and then drops suddenly at a certain temperature T_c.     

Magnetic phase diagram of multiferroic Eu1−xLuxMnO3 investigated by infrared spectroscopy

This work reports on the temperature dependence of the infrared reflectivity of multiferroic Eu_1−xLu_xMnO₃, with 0 ≤ x ≤ 0.3. The semi-quantum model of dielectric function is used in order to extract the effective complex optical conductivity from the power reflectivity spectra. The analysis of the temperature dependence of very general global spectroscopic functions allows the observation of subtle modifications that stem from the stabilization of different magnetic phases. The phase diagram inferred from the spectroscopic data is presented and compared with that previously reported for the mixed system.     

Isobaric specific heat capacity of {xH2O + (1 − x)NH3} with x = (0.0000, 0.1566, 0.1597, 0.3030, 0.3048, 0.4956, 0.7061, and 0.8489) at T = (280, 300, 320, and 360) K over the pressure range from (0.1 to 15) MPa

Measurements of the isobaric specific heat capacity of {xH₂O + (1 ? x)NH₃} with x = (0.0000, 0.1566, 0.1597, 0.3030, 0.3048, 0.4956, 0.7061, and 0.8489) were carried out by the calorimeter with the thermal relaxation method, which we have developed, at T = (280, 300, 320, and 360) K over the pressure range from (0.1 to 15) MPa. The comparison of the present c_p values with the literature data as well as the calculated c_p values by the equations of state (EoS) is presented. The behaviour of the present c_p values are correlated as a function of temperature, and mole fraction, at p = 5 MPa.     

Beneficial modification of the properties of multiferroic BiFeO3 by cation substitution

The effects of modifying the well-known multiferroic BiFeO₃ by substituting Fe by Mn and Bi by La have been investigated. It is shown that both the substitutions have a favourable effect on the multiferroic properties of BiFeO₃. Thus, both BiFe_1−xMn_xO₃ and Bi_1−xLa_xFeO₃ (x = 0.0–0.3) show increased magnetization accompanied by hysteresis loops as well as improved dielectric properties. The ferroelectric transition temperature is lower than that of BiFeO₃, but is in a more accessible range. In Bi_1−xLa_xFeO₃, there is a change in structure at x = 0.2.     

Quaternary (liquid + liquid) equilibria for (water + 2-propanol + 1,1-dimethylethyl methyl ether + diisopropyl ether) at the temperature 298.15 K

(Liquid + liquid) equilibrium tie-lines were measured for one ternary system {x₁H₂O + x₂(CH₃)₂CHOH + (1 − x₁ − x₂)CH₃C(CH₃)₂OCH₃} and one quaternary system {x₁H₂O + x₂(CH₃)₂CHOH + x₃CH₃C(CH₃)₂OCH₃ + (1 − x₁ − x₂ − x₃)(CH₃)₂CHOCH(CH₃)₂} at T = 298.15 K and P^∘ = 101.3 kPa. The experimental (liquid + liquid) equilibrium results were satisfactorily correlated by modified and extended UNIQUAC models both with ternary and quaternary parameters in addition to binary ones.