First-principles calculation of mechanical properties and electronic structures of W4Co4−nXnB4 (X = V,Mn, Fe,Ni; n = 0,1)

The first-principles calculation is performed to explore the mechanical properties and electronic structures of transition elements X (X = V, Mn, Fe, Ni) doped WCoB (tungsten cobalt boron), which has shown high oxidation resistance and melting point under high pressure. The energy analysis indicates that the high pressure leads to the lower lattice constants and less stable structures. The deviation of cohesive energy and formation enthalpy between doped and undoped structures indicates that W₄Co₃FeB₄ and W₄Co₃NiB₄ have similar stability. The high pressure contributes to the increasing of elastic, shear, and bulk moduli, which indicates the increase of covalence. The increase of Poisson's ratio, B/G ratio, and anisotropy index A^U indicates the higher ductility and higher anisotropy under high pressure. Based on bulk modulus and shear modulus, the hardness of W₄Co₄B₄, W₄Co₃FeB₄, and W₄Co₃NiB₄ increases under high pressure, which consists of the variation of electronic structures. The density of states (DOS) and partial DOS analysis indicate that the high pressure leads to lower density around Fermi level and higher hybridization. W₄Co₄B₄, W₄Co₃FeB₄, and W₄Co₃NiB₄ show similar variation of mechanical properties, which is determined by the similar atom properties of Co, Fe, and Ni. Similarly, W₄Co₃VB₄ and W₄Co₃MnB₄ also imply similar variation of mechanical properties and electronic structures.     

Physical–chemical property and activity evaluation of LaB0.5Co0.5O3 (B = Cr,Mn, Cu) and LaMnxCo1−xO3 (x = 0.1, 0.25, 0.5) nano perovskites in VOC combustion

The correlation between physical–chemical properties and activities of LaB_0.5Co_0.5O₃ (B = Cr, Mn, Cu) nano perovskites was studied in combustion of toluene. LaMn_0.5Co_0.5O₃ showed the highest activity among LaB_0.5Co_0.5O₃ catalysts and further optimization study was focused on LaMn_xCo_1?xO₃ (x = 0.1, 0.25, 0.5). The activity and reducibility of catalysts improved due to partial substitution of Co³⁺ by B cation. No direct relationship was between surface area and catalyst activity. T_50% of 2-propanol over LaMn_0.25Co_0.75O₃, LaMn_0.5Co_0.5O₃, LaMn_0.1Co_0.9O₃ and LaCoO₃ was 168, 200, 220 and 229 °C, respectively. LaMn_0.25Co_0.75O₃ was the optimum catalyst and showed robust stability in combustion of toluene and 2-propanol.     

Catalytic activity of nanometer La1−xSrxCoO3 (x = 0, 0.2) perovskites towards VOCs combustion

Combustive oxidation of volatile organic compounds (VOCs), such as propyl alcohol, toluene and cyclohexane, were studied. The combustion was catalyzed by nanoparticles of La_1−xSr_xCoO₃ (x = 0, 0.2) perovskites prepared by a co-precipitation method. The results showed high activities of the perovskite catalysts. Compared to LaCoO₃, in particular, La_0.8Sr_0.2CoO₃ was much higher in catalytic ability. The total oxidation of VOCs followed the increasing order: cyclohexane < toluene < propyl alcohol. The T_99% of cyclohexane was 40 °C lower than that of toluene, which appeared to be determined by the bond strengths of the weakest C–H and C–C bonds. The 100-h stability experiments showed that La_1−xSr_xCoO₃ (x = 0, 0.2) perovskite was highly stable.     

The first metal chelate of un-substituted 2,6-pyridine-dicarboxamide (pdcam): synthesis,molecular and crystal structure,and properties of [CuII(pdc)(pdcam)] · 2H2O (pdc = 2,6-pyridine-dicarboxylato(2−) ligand)

The compound (2,6-pyridine-dicarboxamide)(2,6-pyridine-dicarboxylato)copper(II) dihydrate ([Cu(pdc)(pdcam)] · 2H₂O, compound 1) has been synthesised by reaction of Cu₂(CO₃)(OH)₂, H₂pdc acid and pdcam in an aqueous-ethanol medium. The new compound has been characterised by thermal, spectral, magnetic and X-ray diffraction methods. Its crystal consists of a 3D hydrogen bonded network where all N–H(amide) bonds of pdcam act as H-donors for O carboxyl(pdc) or water acceptor atoms. The Cu(II) atom exhibits an elongated octahedral coordination, type 4 + 2. Both pdc and pdcam ligands define a nearly orthogonal dihedral angle (88.4°). The anionic pdc acts as mer-NO₂(equatorial) tridentate ligand, supplying three among the four closest to the metal donor atoms (Cu–N 1.913(2), Cu–O 2.022(2) and 2.055(2) Å). The diamide pdcam ligand displays a mer-N(equatorial) + O₂(apical) role (Cu–N 2.007(2), Cu–O(amide) 2.295(2) and 2.305(2) Å), thus showing a remarkable conformational flexibility.     

Crystal structure,mixture behavior,and microwave dielectric properties of novel temperature stable (1 − x)MgMoO4 − xTiO2 composite ceramics

Novel temperature stable MgMoO₄–TiO₂ microwave dielectric ceramics were prepared by a solid state reaction process at low temperature (950 °C). As TiO₂ content increases, the relative permittivity increases while the Q × f value decreases, and the variation mechanisms are proposed, respectively. The temperature coefficient of resonant frequency (τ_f) shifts to the positive direction as TiO₂ is added. The mixture mechanisms of τ_f value for two-phase composite materials are supposed. A near-zero τ_f value (3.2 ppm/°C) is obtained when x = 0.3, with ε_r = 9.13 ± 0.03 and Q × f = 11,990 GHz. The 0.7MgMoO₄–0.3TiO₂ composites are considered to be appropriate as a low temperature co-fired ceramic material for microwave wireless communication applications.     

Demixing pressures of hydroxy-terminated poly(dimethylsiloxane)–carbon dioxide binary mixtures at 313.2 K, 323.2 K and 333.2 K

The phase behavior of PDMS(OH)–CO₂ binary mixtures was investigated. Two different molecular weight PDMS(OH) were utilized and the demixing pressures were determined at three temperatures for a wide composition range. Both of these polymers were found to form miscible mixtures with CO₂ at all compositions at pressures lower than 31 MPa in the temperature range 313.2–333.2 K. Depending on the composition of the binary mixtures, two types of phase separation was observed during depressurization; the bubble point and the cloud point. In addition, at specific weight fractions a color change was also observed which was attributed to the mixture critical point. The demixing pressures were observed to increase with temperature and decrease with increasing polymer weight fraction. In addition, higher demixing pressures were obtained for the higher molecular weight polymer mixtures. The bubble point data were modeled by using Sanchez–Lacombe equation of state (SLEoS) and the binary interaction parameters were regressed at the studied temperatures. It was observed that the binary interaction parameters decreased with increasing temperature.     

Construction of three-dimensional Ln–Ag (Ln = Eu; Tm) coordination polymers based on isonicotinate and oxalate ligands

Hexanuclear 4d–4f heterometallic coordination polymers, [Ln₂Ag₄(IN)₅(ox)₂(NO₃)(H₂O)₂ · 3H₂O] [Ln = Eu (1), Tm (2); IN = isonicotinate and ox = oxalate], have been synthesized by hydrothermal reaction of mixed organic ligands and metal salts. Both structures display the same unusual 3D heterometallic coordination frameworks based on rare zigzag lanthanide–oxalate–silver chains, Ag₂(IN)₃ units and IN linkers. The photoluminescent properties of complex 2 were studied.     

Synthesis method comparison of compositionally complex rare earth-based Ruddlesden–Popper n = 1 T′-type cuprates

The multicomponent approach has been successfully expanded to the Ruddlesden–Popper structure with the synthesis of two different high-entropy cuprate compositions: (La_0.2Nd_0.2Gd_0.2Tb_0.2Dy_0.2)₂CuO₄ and (La_0.2Pr_0.2Nd_0.2Sm_0.2Eu_0.2)₂CuO₄. The effect of synthesis method is explored using both solid-state reaction and polymeric steric entrapment (PSE) methods. It is found that PSE leads to more randomly distributed cation species, providing an advantageous method of synthesis for the growing field of high entropy oxides. In situ high-temperature x-ray diffraction tracks the amorphous to crystalline phase transformation in (La_0.2Nd_0.2Gd_0.2Tb_0.2Dy_0.2)₂CuO₄ powder, synthesized using the PSE method. Using the High-Temperature XRD data, a method for gaining information on the kinetic behavior is also applied. Magnetometry of both compositions indicates ferrimagnetic behavior at low temperatures.     

Theoretical investigation of mixed-ligand lanthanocene complexes, (η5-C5H5)2LnX · OC4H8 (Ln=La,Gd, Lu; X=F,Cl, Br,I)

For the first time, density functional theory (DFT) calculation was performed on the titled complexes and the calculated geometries are in good agreement with the available experimental data. The decrease in the bond distances (Ln–X) as well as the increase in the Hirshfeld charges and the chemical hardness from La to Lu indicates an increase in ionic character on going from La to Lu. The lanthanide contraction and ionic character of metal–ligand bond are found to follow the order: Ln–X > Ln–Cp > Ln–O.     

Novel chains constructed from heterotrinuclear units and 1,2-bis(4-pyridyl)ethane formulated as [M2M′(O2CPh)6](bpa) (M = Co,Zn, M′ = Co,Cd): Their catalytic activity

Three novel heterometallic complexes containing two bridging ligands bpa and benzoate, formulated as [M₂M′(O₂CC₆H₅]_n(bpa)_n (bpa = 1,2-bis(4-pyridyl)ethane, M₂M′ = Zn₂Co (1), Zn₂Cd (2), and Co₂Cd (3)), have been synthesized. All three compounds show one-dimensional structures containing linear heteronuclear coordination units linked by bridging bpa ligands. Reactivity study of the compounds 1–3 for the transesterification of a variety of esters has shown that they are very efficient and 2 is the best among them.     

Structure and electrical conductivity of BaCe0.7In0.1A0.2O3−δ (A = Gd,Y) ceramics

BaCe_0.7In_0.1A_0.2O_3?δ (A = Gd, Y) ceramics were synthesized by solid state reaction method. The microstructure and electrical properties of BaCe_0.7In_0.1A_0.2O_3?δ ceramics were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and complex impedance analysis at intermediate temperatures of 773–1073 K in different atmospheres. All BaCe_0.7In_0.1A_0.2O_3?δ ceramics exhibit a cubic perovskite structure. Relative densities of BaCe_0.7In_0.1A_0.2O_3?δ ceramics are above 92%. BaCe_0.7In_0.1Gd_0.2O_3?δ and BaCe_0.7In_0.1Y_0.2O_3?δ ceramics exhibit an excellent chemical stability against boiling water. The conductivity values of BaCe_0.7In_0.1Gd_0.2O_3?δ are higher than those of BaCe_0.7In_0.1Y_0.2O_3?δ in both air and dry hydrogen atmospheres. The highest conductivity is 4.6 × 10^?2 S cm^?1 for BaCe_0.7In_0.1Gd_0.2O_3?δ ceramic in air at 1073 K. BaCe_0.7In_0.1Gd_0.2O_3?δ ceramic with a conductivity value of 1.0 × 10^?2 S cm^?1 at 823 K in both air and dry hydrogen atmospheres is considered as a promising alternative for electrolytes of SOFC in view of decreasing the operating temperature and keeping both high conductivity and good chemical stability.     

Electrical characterization of room temperature humidity sensors in La0.8Sr0.2Fe1−xCuxO3 (x = 0, 0.05, 0.10)

Semiconducting oxide gas sensors based on La_0.8Sr_0.2Fe_1?xCu_xO₃ (x = 0, 0.05, 0.10) (LSF, LSFC05, and LSFC10, respectively) were prepared by screen-printing for humidity detection at room temperature.The thick-films were heat-treated at 800, 900 and 1000 °C for 1 h and all the compositions proved to be effective in humidity sensing and presented a good reproducibility between several measurements. However, the best results were obtained with LSFC10 fired at 800 °C which showed a detection limit of 15% relative humidity and a maximum sensor response of about 87%, higher than the previous results. Copper addition to lanthanum strontium ferrites proved to be effective in lowering the sensors’ detection limit.     

Liquid–Liquid Equilibria of Ternary Systemscis-1,2-Dimethylcyclohexane + Toluene + Sulfolane

Liquid–Liquid Equilibrium (LLE) data for three Ternary Systems comprising cis-1,2-dimethylcyclohexane + toluene + sulfolane were measured at 298.15, 313.15 and 328.15 K under atmospheric pressure. The phase diagrams for the ternary systems were presented. The reliability of the experiment data was tested using the Othmer–Tobias correlation. The LLE data were then correlated with the universal functional activity coefficient for liquid–liquid systems (UNIF-LL) and non-random two liquid using dataset 2 (NRTL/2) activity coefficient models to obtain the binary interaction parameters as programmed by the Aspen Plus simulation. The results showed that the experimental data were satisfactorily represented by both the UNIF-LL and the NRTL/2 models as revealed from the very small values of the root mean square error and the absolute deviation in composition.     

Heterogeneous oxidation of 2-octanol on 5 wt%Pt–1 wt%Bi/Carbon catalyst

The low activity of 5%Pt–1%Bi/Carbon for the oxidation of 2-octanol at atmospheric pressure and 343 K was investigated. Using solvents such as heptane and p-xylene, it was shown that the reaction rates decrease dramatically shortly after the start of the reaction due to poisoning by product adsorption. Hence this work investigates the effect of using different solvent mixtures on the oxidation reaction of 2-octanol with 5%Pt–1%Bi/Carbon. Mixtures with different volumetric ratios of heptane and dioxane were investigated to find the best composition capable of effectively removing the adsorbed amphiphilic ketone. It is apparent that the reaction rate is correlated with the adsorption coefficient of ketone on the catalyst, such that the maximum reaction rate occurs at the lowest ketone adsorption coefficient, corresponding to a concentration of 16–18%v/v dioxane. A model based on a Langmuir–Hinshelwood mechanism has been successfully fitted to the experimental rates.     

Synthesis and optical properties of Ce0.95Pr0.05−xMxO2 (M = Mn,Si) as potential ecological red pigments for coloration of plastics

Ecological red pigments Ce_0.95Pr_0.05?xM_xO₂ (M = Mn, Si) have been synthesized by conventional solid-state route and characterized by X-ray diffractometer, scanning electron microscope and UV–vis spectroscopy. Mn⁴⁺/Si⁴⁺ was incorporated into the CeO₂–PrO₂ system to tune the color properties of the pigments by shifting the optical absorption edge. Si⁴⁺ substitution blue shifts the absorption edge of Pr-doped ceria and shows bright reddish brown color. Mn⁴⁺ substitution stabilizes the absorption edge and exhibits dark brown hue. The coloring mechanism is based on the shift of charge transfer band of CeO₂ to higher wavelength by co-substitution of Pr⁴⁺ and tetravalent metal ions in ceria. Si co-doped pigments possess smaller particles and hence exhibit more lightness compared to Mn co-doped samples. The reddish brown pigments exhibit very good coloring performance in polymer matrix. These Ce_0.95Pr_0.05?xM_xO₂ (M = Mn, Si) pigments have potential to be used as ecological red pigments for coloration of plastics.     

Heteropolynuclear Schiff-base complexes Cu–Ln–Fe (Ln = Sm & Pr) with magnetic property

Two new complexes [{CuL}Sm(H₂O)₃{Fe(CN)₆}]₂·6H₂O (1) [{CuL}₂Pr(H₂O){Fe(CN)₆}]₂·4H₂O (2) (H₂L = N,N′-ethylenebis(3-methoxysalicylideneimine)) have been prepared by reactions of acyclic compartmental Schiff-base heterodinuclear 3d–4f compound [{CuL}Ln(NO₃)₃] (Ln = Sm & Pr) with K₃[Fe(CN)₆]. Crystal structures of both 1 and 2 reveal unique topology structures. 1 shows a dimeric heterotrinuclear [{CuL}Sm(H₂O)₃{Fe(CN)₆}]₂ while 2 displays a dimeric heterotetranuclear [{CuL}₂Pr(H₂O){Fe(CN)₆}] with distorted sandwich moieties [{CuL}₂Pr]. Both 1 and 2 form similar 1D ladder-like structure through the intermolecular double bridges of Cu–N bonds. The measurement of variable-temperature magnetic susceptibility reveals that both complexes 1 and 2 exhibit antiferromagnetic interaction between spin carriers.     

Figure of merit enhancement in thermoelectric materials based on γ-Ln0.8Yb0.2S1.5-y (Ln = Gd,Dy) solid solutions

Here we report the study temperature dependencies of the Seebeck coefficient, the electrical resistivity (T = 300–750 K), the total thermal conductivity (T = 300–973 K), and the thermoelectric figure of merit (T = 300–750 K) of ceramic samples of γ-Ln_0.8Yb_0.2S_1.5-y (Ln = Gd, Dy) solid solutions. It was found that Yb³⁺ ions in γ-Ln_0.8Yb_0.2S_1.5-y act as the promoters of higher crystallite nucleation rate during the formation of solid solutions. This results in the sample dispersion increase and the formation of the additional phonon scattering centers (dislocations and strain stresses along the crystallites semi-coherent boundaries). These features of the real structure determined the low value of thermal conductivity of γ-Ln_0.8Yb_0.2S_1.5-y solid solutions. The lowest electrical resistivity 20 μΩ m at 750 K and the thermal conductivity 0.58 W/m K at 973 K, the highest Seebeck coefficient 125 μV/K at 700 K and the maximum thermoelectric efficiency, ZT = 0.60 (at 770 K) were obtained for γ-Dy_0.8Yb_0.2S_1.5-y.