Calculated structural properties of TbCu7-type disordered intermetallic compounds NdCo7 and Nd1−xYxCo6.8Zr0.2 (x = 0, 0.2, 0.4, 0.6)

An improved evolution from ordered CaCu₅-type structure to disordered TbCu₇-type structure has been implemented in this work based on the atomic simulation regarding intermetallic compounds NdCo₇ and Nd_1?xY_xCo_6.8Zr_0.2 (x = 0, 0.2, 0.4, 0.6). The calculated powder patterns, phase stabilities, site preferences and structural properties, including lattice parameters, the shrinkages from 2c to 6l site in 2c layers, the 3g layer deformation, the dumbbell bond length distribution and inclination angle distribution as well as the effects of element Zr and Y in the compounds, are found to be in agreement with physical analysis and experiment.     

Calorimetric and computational study of 7-hydroxycoumarin

The standard (p° = 0.1 MPa) molar energy of combustion in oxygen, at T = 298.15 K, of 7-hydroxycoumarin was measured by static bomb calorimetry. The value of the standard molar enthalpy of sublimation was obtained by Calvet microcalorimetry and corrected to T = 298.15 K. Combining these results, the standard molar enthalpy of formation of the compound, in the gas phase, at T = 298.15 K, has been calculated, ?(337.5 ± 2.3) kJ · mol^?1. The values for the temperature of fusion, T_fusion, and for the fusion enthalpy, at T = T_fusion, are also reported.Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional with extended basis sets, the MC3BB and MC3MPW methods and more accurate correlated computational techniques of the MCCM suite have been performed for the compound.The agreement between experiment and theory gives confidence to estimate the enthalpy of formation of the remaining hydroxycoumarins substituted in the benzene ring.     

Isothermal (vapour + liquid) equilibrium (VLE) for binary mixtures containing diethyl carbonate,phenyl acetate,diphenyl carbonate,or ethyl acetate

The isothermal (vapour + liquid) equilibrium (VLE) (P–T–x_i–y_i) was determined the binary systems of (ethyl acetate + diethyl carbonate) from T = (373.2 to 453.2) K, (ethyl acetate + phenyl acetate) at T = 373.2 K, and (diethyl carbonate + phenyl acetate) at T = 373.2 K, while the VLE (P–T–x_i) of three diphenyl carbonate-containing binary systems was also determined experimentally at temperatures from (373.2 to 453.2) K. The experimental results show no azeotrope formation and near ideal solution behaviour for each binary system. These new VLE (P–T–x_i–y_i) data have been passed by the point, area, and infinite dilution thermodynamic consistency tests. The Wilson-HOC, the NRTL-HOC, and the UNIQUAC-HOC models were applied to correlate the VLE results and the optimal values of the model parameters have been determined through data reduction. Comparable results were obtained from these three models.     

Li6B18(Li2O)x – A boride with a porous framework of B6 octahedra

The synthesis and crystal structure of the red transparent lithium boride Li₆B₁₈(Li₂O)_x (0 < x ≤ 1) is reported. The lattice constants are a = 8.21708(17) Å and c = 4.15893(16) Å for x = 0.26 (powder data), a = 8.223(4) Å and c = 4.160(2) Å for x = 0.7 (single crystal data), a = 8.21179(16) Å and c = 4.14485(13) Å for x = 0.9 (powder data). The compound crystallizes in the space group P6/mmm (no. 191). The crystal structure consists of B₆ octahedra forming a 3-dimensional network with large open channels. This compound has remarkable topological similarities with hexagonal tungsten bronzes and zeolites and is only formed, when a template is present during the synthesis.     

Thermodynamics of transfer of naphthalene and 2-naphthoic acid from water to (water + ethanol) mixtures at T=298.15 K

Standard thermodynamic functions of transfer of naphthalene and 2-naphthoic acid from water to (water + ethanol) mixtures at T=298.15 K have been determined from solubility measurements at different temperatures. Standard free energies of transfer of both naphthalene and 2-naphthoic acid showed decreasing tendency with the increasing x(EtOH), and the standard entropy and enthalpy of transfer exhibited a change of double peaks with x(EtOH). The Δ_trG⁰ of 2-naphthoic acid decreased more rapidly than that of naphthalene when x(EtOH) < 0.746 and lower than that of naphthalene when x(EtOH) >0.746 at T=298.15 K. The double peaks in the curves of standard entropy and enthalpy of transfer illustrated that the microstructure of the series of mixed solvents of (water + ethanol) underwent a variable process from ordered to disordered and then from disordered to ordered. The results mean that there is a relatively ordered structure near x(EtOH)=0.13 in the (water + ethanol) solutions besides the existence of a clathrate structure in the water-rich region.     

Magnetoelectric perovskite (Bi0.5Pb0.5)(Fe0.5Zr0.5)O3: Preparation,structural and magnetic properties

The perovskite (Bi_0.5Pb_0.5)(Fe_0.5Zr_0.5)O₃ was synthesized by solid-state reaction in an attempt to find magnetoelectric materials, in which ferroelectricity and ferromagnetism coexist. This complex perovskite has been studied by X-ray and neutron powder diffraction in combination with magnetic measurements. The compound crystallizes in the orthorhombic space group Pbam with a ～ √2a_p, b ～ 2√2a_p and c ～ 2a_p (with a_p ～ 4.057 Å). The field and temperature dependence of the magnetization combined with neutron diffraction data showed antiferromagnetic behavior with the Neel temperature, T_N ～ 450 K. Rietveld refinements of neutron powder diffraction data collected at different temperatures, between 10 and 700 K, have been carried out in order to extract information about the thermal evolution of the nuclear and magnetic structures. A distorted orthorhombic perovskite structure was found within the whole temperature interval. The Bi/Pb and Fe/Zr ions were found to be partially ordered over the perovskite A-site and disordered over the B-site. The neutron diffraction patterns of the (Bi_0.5Pb_0.5)(Fe_0.5Zr_0.5)O₃ sample showed evidence of a long-range magnetic ordering below T_N with a propagation vector k = (0,0,0) and an antiferromagnetic arrangement of the magnetic moments of the Fe³⁺ cations in the B-site. This is consistent with an A_y-type magnetic structure. The factors governing the structural and magnetic properties of (1 ? x)BiFeO₃–xPbZrO₃ solid solutions are discussed and compared with those of pure BiFeO₃ and PbZrO₃. A solid solution strategy for developing magnetoelectric properties in BiFeO₃-based compounds is described, with the aim of realizing both a spontaneous polarization and magnetization at room 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.     

Compressed liquid densities for the (n-heptane + n-decane) and (n-octane + n-decane) systems from T = (313 to 363) K

Densities (p, ρ, T, x₁) of two binary n-alkane systems are reported from T = (313 to 363) K in the compressed liquid phase up to 25 MPa over the whole range of composition. The binary mixtures {x₁n-heptane + (1 ? x₁)n-decane} and {x₁n-octane + (1 ? x₁)n-decane} were prepared at compositions of (x₁ = 0.0531, 0.2594, 0.5219, 0.777, 0.952), and (x₁ = 0.0616, 0.2801, 0.5314, 0.7736, 0.9623), respectively. A measuring system based on a vibrating tube densimeter, DMA HPM from Anton Paar with data acquisition system was developed in order to obtain experimental densities. Water and nitrogen were used as reference fluids to calibrate the densimeter. Experimental methodology was checked by comparing the n-heptane and n-decane densities against multi-parameter equations proposed in the literature. Differences between both sets of data show a maximum deviation of 0.07%. Excess molar volumes, isothermal compressibility and isobaric thermal expansivity were computed from experimental densities.     

Thermal properties of [Cr(NH3)6](BF4)3 studied by adiabatic and relaxation calorimetry

Four (solid–solid) phase transitions were detected in the temperature range of (9 to 300) K in polycrystalline [Cr(NH₃)₆](BF₄)₃ at T_C1 = 240.7 K, T_C2 = 108.0 K, T_C3 = 91.9 K, and T_C4 = 61.3 K by adiabatic calorimetry. The measurements by relaxation calorimetry were followed on lowering temperature from 20 K down to 0.35 K under six different external magnetic field values (9, 7, 5, 3, 1 and 0) T. For non-zero values of applied magnetic field well-defined Schottky anomaly appears. Magnetic heat capacity was calculated assuming the zero-field splitting for the decoupled Cr(III) ions. There is no discrepancy between the observed and calculated values. Isothermal magnetization curve recorded up to 5 T was measured at temperature of 1.8 K.     

Magnetic dilution effect on the charge transfer phase transition and the ferromagnetic transition for an iron mixed-valence complex, (n-C3H7)4N[FeII1−xZnIIxFeIII(dto)3] (dto = C2O2S2)

Iron mixed-valence complex, (n-C₃H₇)₄N[Fe^IIFe^III(dto)₃] (dto = C₂O₂S₂) shows a new-type of phase transition coupled with spin and charge around 120 K, where the charge transfer between the Fe^II and Fe^III sites occurs reversibly, and shows the ferromagnetic transition at 7 K. To investigate the magnetic structure and its dimensionality of (n-C₃H₇)₄N[Fe^IIFe^III(dto)₃], we have synthesized a mixed crystal system, (n-C₃H₇)₄N[Fe^II_1?xZn^II_xFe^III(dto)₃], and measured its magnetic properties. In this system, the magnetic moment is reduced with increasing of Zn ratio. Moreover, the ferromagnetic interaction changes to the antiferromagnetic one and the remnant magnetization disappears between x = 0.48 and 0.96, while the charge transfer between the Fe^II and Fe^III sites disappears above x = 0.26. In this paper, we present the magnetic dilution effect on the charge transfer phase transition and the ferromagnetic transition by means of magnetic susceptibility measurement and ⁵⁷Fe Mössbauer spectroscopy.     

Achieving high-rate capacitance of multi-layer titanium carbide (MXene) by liquid-phase exfoliation through Li-intercalation

The stacks of multi-layer Ti₃C₂T_x and other types of MXene materials limit their electrochemical performance. Herein, we report a facile exfoliation technique to improve the exfoliation efficiency through Li-intercalation into Ti₃C₂T_x interlayers in isopropyl alcohol (IPA) with LiOH as intercalant. This de-intercalation method presented here not only effectively delaminates the stacked Ti₃C₂T_x multi-layers into separate few-layer MXene sheets, but also achieves high-rate supercapacitive performance of Ti₃C₂T_x electrode. The as-produced delaminated Ti₃C₂T_x shows highly improved electrochemical capacitive properties from 47 to 115 F g^− 1 at 200 mV s^− 1. Even at extremely high scan rate of 1000 mV s^− 1, a specific capacitance of 82 F g^− 1 is still obtained. The high-rate capability can be attributed to improved ions accessibility into the few-layer structures. This study offers a new and simple exfoliation pathway for MXenes materials to exploit their full potential in energy storage applications.     

Thermochemical properties of 4-N,N-dialkylamino-7-nitrobenzofurazan derivatives (alkyl = methyl,ethyl)

The standard (p° = 0.1 MPa) molar enthalpies of formation, at T = 298.15 K, in the gaseous phase, for two nitrobenzofurazan derivatives, 4-N,N-dimethylamino-7-nitrobenzofurazan (DMANBF) and 4-N,N-diethylamino-7-nitrobenzofurazan (DEANBF), were derived from their enthalpies of combustion and sublimation, obtained by static bomb calorimetry and by the Knudsen effusion technique, respectively. The results are compared with the corresponding data calculated by the G3(MP2)//B3LYP approach. Computationally, the molecular structures of both compounds were established and the geometrical parameters were determined at the B3LYP/6-31G(d) level of theory.     

Thermodynamic modelling of the partially ordered solid solution Hf5−xNbxGe4 supported by ab initio calculations

The site preferences in the solid solution phase Hf_5−xNb_xGe₄ (0 < x < 3.8) were modelled with the “Compound Energy Formalism” model. The ground state energies of the end members calculated from ab initio density functional theory were taken as input parameters for the model. These ground state energies were computed for models with either fixed atomic positions or fully relaxed structures. The results of the former computation were used for the construction of a simplified model. Site fractions modelled with both, original and simplified models fit well to the experimental values, confirming the almost stepwise substitution mechanism in this compound. Non-linear trends of the lattice parameters found experimentally could be reproduced very well.     

Pressure response of the bimetallic chain compound MnNi(NO2)4(en)2; en = ethylenediamine

The compound MnNi(NO₂)₄(en)₂, en = ethylendiamine, is a rare example of a ferromagnetically coupled bimetallic chain (J_∥ chain ∼ 2–3 K). Further, for this material, a finite inter-chain coupling triggers an antiferromagnetic (AFM) transition below T_N = 2.3 K. Here, we present a susceptibility study of MnNi(NO₂)₄(en)₂ under pressure. From our data, we derive the pressure response of the antiferromagnetic transition temperature T_N. Even up to highest pressure of 8.2 kbar we find a very modest increase of T_N by only ∼0.1 K. Independently, from a pressure study of the lattice parameters of MnNi(NO₂)₄(en)₂, we calculate the bulk module of the material to ∼8.8 GPa. Combining the data T_N(p) with the bulk module yields an anomalously low Grüneisen parameter Γ_mag of only 0.5(5). We discuss possible scenarios accounting for such a low Grüneisen parameter.     

Density,viscosity, refractive index,excess molar enthalpy,viscosity, and refractive index deviations for the (1-butanol + 2-butanone) binary system at T = 303 K. A new adiabatic calorimeter for heat of mixing

Density, viscosity, refractive index, and heat of mixing measurements for {x₁ 1-butanol + (1 ? x₁) 2-butanone} at T = 303 K were made over the whole concentration range. Data of the binary mixture were further used to calculate the viscosity and refractive index deviations, and excess molar enthalpy. The excess or deviation properties were fitted with the Redlich–Kister polynomial relation to obtain their coefficients and standard deviations. The construction of an adiabatic calorimeter useful in the neighbourhood of room temperature is described. Its performance was checked by measuring the heat of mixing for {x₁ benzene + (1 ? x₁) cyclohexane} over the whole concentration range at T = 298 K. Experimental results are within a standard deviation of 9 J · mol^?1 of the accepted literature values.     

Raman investigation of the order-disorder phase transitions in the 2[N(C3H7)4]SbCl4 compound

The Raman spectra of bis (tetrapropylammonium tetrachloroantimonate (III)) 2[(C₃H₇)₄N]SbCl₄ compound single crystals were studied in the wavenumber range from 3500 to 50 cm⁻¹ for temperatures between 300 and 415 K. Two phase transitions occurring at 343 (T_tr1) and 363 K (T_tr2) were observed and characterized. The strong evolutions of the Raman shift, half-widths and intensity of many lines associated with the organic cations were observed with discontinuities in the vicinity of the two phase transitions. The most important changes were noticed for the band at 307 cm⁻¹ (at room temperature) assignable to the torsion of CH₃ groups of the cations. The spectral characteristics of this band was analyzed and consistently described in the framework of an order–disorder model for the two phase transitions. They allowed us to obtain information relative to the activation energy, the correlation length, and the critical exponent of the mechanism. The decrease of the estimated activation energies for the band 307 cm⁻¹ with the increase in temperature has been interpreted in terms of a change in the reorientation motion of cations. The temperature dependence of the reduced peak intensity allowed for the determination of the critical exponents and evolution of the correlation length on approaching the transition.     

Synthesis,structure and properties of Ag2PdO2

The first silver palladium oxide, Ag₂PdO₂, was synthesised from a co-precipitated oxide precursor by annealing at 423–823 K, applying an oxygen pressure of 73 MPa. The crystal structure has been determined from X-ray and neutron powder diffraction data. The new compound crystallises in space group Immm. The lattice constants as determined from X-ray powder diffraction are a=4.55523(5) Å, b=3.00803(3) Å and c=9.8977(1) Å. The crystal structure constitutes a new structure type showing some features in common with the Li₂CuO₂-type. Palladium is found in a nearly square planar arrangement while silver has an almost linear co-ordination. The overall structure can be considered as a rocksalt defect structure. Ag₂PdO₂ is diamagnetic and semiconducting. The band gap, estimated from conductivity measurements in the temperature range of 240–300 K, is 0.18(2) eV.     

Electrochemical properties of Li(Li(1−x)/3CoxMn(2−2x)/3)O2 (0 ⩽ x ⩽ 1) solid solutions prepared by poly-vinyl alcohol (PVA) method

The whole range of solid solutions Li(Li_(1−x)/3Co_xMn_(2−2x)/3)O₂ (0 ⩽ x ⩽ 1) was firstly synthesized by an aqueous solution method using poly-vinyl alcohol as a synthetic agent to investigate their structure and electrochemical properties. X-ray diffraction results indicated that the synthesized solid solutions showed a single phase without any detectable impurity phase and have a hexagonal structure with some additional peaks caused by monoclinic distortion, especially in the solid solutions with a low Co amount. In the electrochemical examination, the solid solutions in the range between 0.2 ⩽ x ⩽ 0.9 showed higher discharge capacity and better cyclability than LiCoO₂ (x = 1) on cycling between 2.0 and 4.6 V with 100 mA g⁻¹ at 25 °C. For example, Li(Li_0.2Co_0.4Mn_0.4)O₂ (x = 0.4) exhibited a high discharge capacity of 180 mA h g⁻¹ at the 50th cycle. By synthesizing the solid solution between Li₂MnO₃ and LiCoO₂, the electrochemical properties of the end members were improved.