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.     

Phase behavior of catalytic deactivated compounds and water with 1-ethyl-3-methylimidazolium acetate [EMIM][OAc] ionic liquid at T = 298.15–323.15 K and p = 1 bar

Density, surface tension and refractive index of the binary mixture of catalytic deactivated compounds with 1-ethyl-3-methylimidazolium acetate {[EMIM][OAc]} ionic liquid were measured at temperature of 298.15–323.15 K from which the derived thermodynamic properties including excess molar volume and deviation of surface tension and refractive index were calculated. The derived thermodynamic properties could be explained well by the interaction between similar and dissimilar aromatic structure of the molecules over the entire mole fraction of ILs. It was observed that all the catalytic deactivated compounds and water molecules have significant structural interaction with [EMIM][OAc] via CH?π bond interaction, π?π stacking and n?π interaction over the entire mole fraction of IL at T = 298.15 K. Further the composition of ionic liquid have significant influence on the interaction between dissimilar aromatic structure of molecules like pyridine, indoline and quinoline in liquid phase as compared to temperature. The surface tension increases in the order of: hiophene > pyridine > quinoline > pyrrole > indoline > water; while the refractive index increases in the order: pyridine < water < pyrrole < thiophene < indoline < quinoline. The deviation of surface tension was found to be inversely proportional to the deviation of refractive index at T = 298.15 K. From these results it was concluded that the structure of the ionic liquids is very important for extraction processes on catalytic deactivated compounds, especially for pyridine, indoline and quinoline as compared to water molecules.     

Synthesis and electrical properties of Ce1−xGdxO2−x/2 (x = 0.05–0.3) solid solutions prepared by a citrate–nitrate combustion method

Ce_1?xGd_xO_2?x/2 (GDC) powders with different Gd³⁺ contents (x = 0.05–0.3) were prepared by a simple citrate–nitrate combustion method. The influence of the Gd³⁺ doping content on the crystal structure and the electrical properties of GDC were examined. Many analysis techniques such as thermal analysis, X-ray diffraction, nitrogen adsorption analysis, scanning electron microscopy and AC impedance analysis were employed to characterize the GDC powders. The crystallization of the GDC solid solution occurred below 350 °C. The GDC powders calcined at 800 °C showed a typical cubic fluorite structure. The lattice parameter of GDC exhibited a linear relationship with the Gd³⁺ content. As compared with that sintered at other temperatures, the GDC pellet that sintered at 1300 °C had a high relative density of 97%, and showed finer microstructure. The conductivity of GDC was firstly increased and then decreased with the increase of the Gd³⁺ content. The sintered GDC sample with the Gd³⁺ content of 0.25 exhibited the highest conductivity of 1.27 × 10^?2 S cm^?1 at 600 °C.     

Synthesis of Ti2(InxAl1-x)C (x = 0–1) solid solutions with high-purity and their properties

Herein, high-purity Ti₂(In_xAl_1-x)C (x = 0–1) solid solutions were successfully synthesized. The crystal structure and actual composition of solid solutions were confirmed using XRD, SEM, and TEM analyses, and their formation mechanism was revealed by thermal analysis. On the In-rich side (x ≥ 0.5), primary Ti₂InC first formed and then acted as a crystalline seed for the subsequent solid solutions, resulting in a cluster-like morphology. The lattice constants of Ti₂(In_xAl_1-x)C were found to well follow Vegard’s law. The examined properties of Ti₂(In_xAl_1-x)C also greatly depended on their A-site compositions. Ti₂AlC exhibited the highest hardness and elastic moduli, while the best corrosion resistance was achieved at Ti₂InC, and all Ti₂(In_xAl_1-x)C displayed active dissolution in 0.5 M HCl solution. Thus, adjusting the In/Al ratio at A-site can yield a desired set of performances, which provides a good example for regulating the performance of MAX phases via A-site solid solution strategy.     

Aluminum to germanium inversion in mullite-type RAlGeO5: Characterization of a rare phenomenon for R = Y,Sm–Lu

Mullite-type RMn₂O₅ (R = Y, rare-earth element) ceramics are of ongoing research attentions because of their interesting crystal-chemical, physical, and thermal properties. We report a detailed structural, spectroscopic and thermal analysis of the series of mullite-type RAlGeO₅ (R = Y, Sm-Lu) phases. Polycrystalline samples are prepared by solid-state synthesis methods. Each sample is characterized by X-ray powder diffraction followed by Rietveld refinements, showing that they are isotypic and crystallize in the space group Pbam. The change of the metric parameters is explained in term of the lanthanide contraction effect. A rare inversion of Al/Ge between octahedral and pyramidal sites have been observed for these mullite-type so called O10 compounds, and the inversion parameter found to be between 0.22(1) and 0.30(1) for different R-cations. The <Al/Ge–O> bond distances and their bond valence sums (BVSs) support the respective inversions. Density functional theory (DFT) calculated phonon density of states (PDOS) and electronic band structures are compared for the vibrational and electronic band gap features respectively. Analysis of UV/Vis absorption spectra using both derivation of absorption spectra fitting (DASF) and Tauc's methods demonstrates that each of the RAlGeO₅ O10 compounds is high bandgap semiconductor, possessing direct transition between 4.1(1) and 5.4(1) eV. Both Raman and Fourier transform infrared spectra show clear red shift (quasi-harmonic) of the vibrational wavenumbers with respect to the ionic radii of the R-cations. Selective Raman bands at higher wavenumber region further complement the inversion of Al/Ge between two coordination sites. The higher decomposition temperature of the RAlGeO₅ compounds, compared to those of RMn₂O₅ phases, is explained in terms of higher bond strength of Al/Ge-O than those of Mn-O. Irrespective to the inversion between Al- and Ge-sites, the decomposition temperature also depends on the type of R-cation in RAlGeO₅.     

Phase formation and dielectric properties of Ln2(Ln′0.5Nb0.5)2O7 (Ln = rare earth element)

Weberites and pyrochlores (A₂B₂O₇), both fluorite-related superstructures, are attractive dielectric ceramics due to their ability to accommodate diverse cations, thus allowing their properties to be tailored. This study focuses on the fundamental understanding of the structure–dielectric property relationships in fluorite-related oxides. Specifically, Ln₃NbO₇ and Ln₂(Ln′_0.5Nb_0.5)₂O₇ (where the ionic radius of Ln′ is smaller than that of Ln) compounds are investigated. It has been previously shown that weberite-type Ln₃NbO₇ exhibits a composition dependent dielectric relaxation above room temperature. It is here shown that a dielectric relaxation also occurs in La₂(Ln′_0.5Nb_0.5)₂O₇ (Ln′ = Yb³⁺, Er³⁺, and Dy³⁺) compounds near or below ?158 °C. The temperature, at which the maximum permittivity occurs, is different for different compositions (?132 °C for La₂(Yb_0.5Nb_0.5)₂O₇, ?197 °C for La₂(Er_0.5Nb_0.5)₂O₇, and ?187 °C for La₂(Dy_0.5Nb_0.5)₂O₇ at 1 MHz) and is correlated with the distortion of the NbO₆ octahedra. The room temperature dielectric permittivity of all three compounds was measured to be between 40 and 50 at 1 MHz.     

Synthesis,Characterization, Reactivity of η 3-allylPd(L)(X), Where X = Cl and L = Imidazolylphosphine and Their Application in Aryl Amination Reactions

Synthesis of new mono-(imidazolylphosphine) palladium chloride complexes is reported. Imidazolyl phosphines reacted with allypalladium chloride dimer to form monophosphine palladium(II) complexes. Some of these complexes readily ionize to form stable square planar complexes in which the heterocyclic nitrogen coordinates to Pd, whereas in other cases, the acidity of the N–H proton was explored. Finally, activity of complexes as catalysts for aryl amination reactions was also investigated.

     

Synthesis and characterization of [S2MoS2Cu(n-SPhF)]2 −(n = o,m, p) clusters: Potential 19F-NMR structural probes for Orange Protein

Three fluorinated Mo–Cu–thiolate isomers, [Ph₄P]₂[S₂MoS₂Cu(n-SPh_F)], [n-SPh_F = 2-fluorothiophenol (1a)], 3-fluorothiophenol (1b), and 4-fluorothiophenol (1c)] were synthesized and spectroscopically characterized. The ¹⁹F-NMR signal of the fluorine atom in the benzene has different chemical shift for each isomer, which is highly influenced by the local environment that can be manipulated by different solvents and solutes. The fluorine-19 chemical shift is an advantageous NMR structural probe in alternative to ¹H-NMR [B.K. Maiti, T. Avilés, M. Matzapetakis, I. Moura, S.R. Pauleta, J.J.G. Moura, Eur. J. Inorg. Chem. (2012) 4159.], that can be used to provide local information on the pocket of the metal cluster in the Orange Protein (ORP).     

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.     

Promotional effect of graphite oxide on surface properties and catalytic performance of La1 − xSrxMnO3 (x = 0,0.1) for methane combustion

The effect of graphite oxide (i.e. GO)/La_1 − xSr_xMnO₃ (x = 0,0.1) catalysts on methane combustion in CNG's (compressed natural gas) exhaust was investigated in current work. GO layer was employed to realize a surface modification. The light-off temperature of methane decreased, and reached the full conversion at 540 °C. The prepared catalysts were also characterized by TEM, surface energy, XPS and H₂-TPR techniques. SEM indicated that the La_1 − xSr_xMnO₃ particles grew dispersedly on GO layer, and surface analysis suggested that the introducing of GO can enhance the adsorption of oxygen groups on the surface of the catalysts.     

Determination of the initial heat treatment temperature in the two-step sintering of xAl–ZnO (x = 1, 2, and 3 wt.%)

The application of a two-step sintering route successfully decreased the sintering temperature of Al-doped ZnO transparent conducting oxide target. The two-step sintering consisted of initial heat treatment (IHT) at 800–1000 °C under mild (<2 MPa) external pressure, and pressureless final sintering at 1250–1350 °C in a separate furnace. The optimum IHTs for effective densification depended on the Al doping. The 800 °C IHT was effective for 1 wt.% Al doping, and the 1000 °C IHT, for 3 wt.% Al doping. As a result of the effective IHT, the volume of the micron sized pore decreased with the fragmentation into submicron pores. This suggests that cohesion of the secondary particles occurred during the effective IHT. The IHT temperature for achieving cohesion increased in the 3 wt.% Al doping. The criterion for determining the IHT in the two-step sintering was identified as the minimum temperature at which the cohesion of secondary particles can be achieved.     

Synthesis of La1−xSrxMO3 (M = Mn,Fe, Co,Ni) nanopowders by alanine-combustion technique

La_1?xSr_xMO₃ (M = Mn, Fe, Co, Ni, x = 0–0.3) powders were obtained by solution combustion technique using metal nitrates and α-alanine. The as-prepared powders, resulted by the combustion reaction, were annealed at different temperatures to investigate the evolution of crystalline phases. For the strontium-doped lanthanum-based perovskites, higher annealing temperatures than for the corresponding pure lanthanum-based perovskites are needed to obtain single-phase compounds depending on M-site metal and strontium content. The oxide powders were investigated by FT-IR spectra, X-ray diffraction (XRD), scanning electron microscopy (SEM) and specific area measurements. Based on our results we propose different mechanisms for La_1?xSr_xMO₃ (M = Mn, Fe, Ni, x = 0–0.3) obtaining, depending on the intermediary compounds formed in the combustion reaction or during the thermal treatment of the as-prepared powders.     

The novel ligand 4′-phenyl-3,2′:6′,3′′-terpyridine (L) and the supramolecular structure of the dinuclear complex [Zn2(μ-L)(acac)4] · H2O (acac = acetylacetonato)

The new terpyridyl ligand 4′-phenyl-3,2′:6′,3′′-terpyridine (L) reacts with Zn(acac)₂ to produce the dizinc complex [Zn₂(μ-L)(acac)₄] · H₂O (1) (acac = acetylacetonato). The analysis of the crystal structure of this zero-dimensional (0D) complex shows the existence of two Zn(acac)₂ centers bridged symmetrically by one μ-L ligand. The key role played by the acac and L ligands and the guest water molecule allows the generation of a series of intermolecular hydrogen bonds of the O–H/O, C–H/O and C–H/π type which give raise to a 3D supramolecular array. The observed C–H/π interactions are so widespread that all the π-rings present in the structure, viz., those belonging to the L ligand as well as the acetylacetonato chelate rings, participate as hydrogen bond acceptors.     

Structural and optical properties of Mg1−xMnxP2O6 (x = 0–1.0) magnesium metaphosphate

Structural and optical properties of Mg_1−xMn_xP₂O₆ (x = 0–1.0) magnesium metaphosphate were investigated in detail. The complete solid solution of MgP₂O₆–MnP₂O₆ is confirmed as monoclinic space group C2/c. The dynamic luminescence was studied by changing the Mn²⁺ content (0–100 mol%) and temperature (10–300 K). There is a good chemical homogeneity in Mg_1−xMn_xP₂O₆ (x = 0–1.0), which can be supported by the linearly varying cell size and the gradually changing vibration spectrum. However, the optical properties of the solid solution do not show a continuous change trend, that is, an obvious inflection point appeared when x = 0.5. Mg_1−xMn_xP₂O₆ (x = 0.1–0.5) shows a dominant O²⁻ → Mn²⁺ charge transfer (CT) absorption in the near UV region and feeble d–d transitions of Mn²⁺ in visible wavelength region. However, Mg_1−xMn_xP₂O₆ (x = 0.6–1.0) presents a strong d–d absorption transition and nearly disappeared CT band. The changing trend of optical absorption is also maintained in the excitation and emission of the solid solutions. In Mg_1−xMn_xP₂O₆ (x = 0.1–0.5), (Mn, Mg)O₆ octahedron has slight distortion, and the effective luminescence only occurs when CT band excitation is used. In contrast, in Mg_1−xMn_xP₂O₆ (x = 0.6–1.0), (Mn, Mg)O₆ octahedron is highly distorted, and only excitation at d–d transition produces effective luminescence. This research highlights the critical role of MnO₆ octahedral distortions in the luminescence properties of Mn²⁺ activators. The research provides a reference for developing optical materials.     

Preparation and microwave dielectric properties of BaLi1+xF3+x (x = 0–0.01) ceramics

BaLi_1+xF_3+x (x = 0–0.01) were successfully mechanosynthesized by a simple ball-milling process. The effects of excessive LiF and sintering method and/or annealing atmosphere on its sintering behavior, microstructure, and microwave dielectric properties have been investigated in this paper. The mechanosynthesized powder can be densified with relative densities of ∼95 % after sintering at 750–800 °C/2 h in N₂. The obtained ceramics exhibit excellent optimized microwave dielectric properties with ε_r of ∼11.46 ± 0.06, Q×f values of 83175 ± 1839 GHz and τ_f of ∼ − 70 ± 3 ppm/°C at the x = 0.006 composition. Its Q×f value could be improved to 94603 ± 2037 GHz) by post-annealing in N₂ after post annealing at 700 °C/2 h. The Q×f value could be further improved to (120,098 ± 2344 GHz) by hot-pressed sintering (HPS). Sintering in the ambient atmosphere or O₂ leads to lower Q×f values than those of the counterparts sintered in N₂ due to the introduction of F-vacancies by oxidation_, while little variation in ε_r andτ_f.     

Catalytic performance of NO oxidation over LaMeO3 (Me = Mn,Fe, Co) perovskite prepared by the sol–gel method

The catalytic performance of LaMeO₃ (Me = Mn, Fe, Co) perovskite prepared by a sol–gel method was studied. These catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption (BET), H₂ temperature programmed reduction (TPR), NO temperature programmed desorption (TPD) and CO–O₂ pulse. LaCoO₃ exhibited the best activity than that of LaFeO₃ and LaMnO₃ even after hydrothermal ageing. The activity sequence is in accordance with the reducibility of the samples. The activated oxygen species and adsorbed NO play key roles in the NO oxidation reaction.     

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.     

Liquid–liquid equilibria for ternary systems of dimethyl carbonate + C1–C4 alcohols + water at 298.15 K and atmospheric pressure

The ternary liquid–liquid equilibria (LLE) of the following systems were analytically determined at 298.15 K and atmospheric pressure using stirred and thermo-regulated cells: {dimethyl carbonate (DMC) + methanol + water}, {DMC + ethanol + water}, {DMC + 1-propanol + water}, {DMC + 2-propanol + water}, {DMC + 1-butanol + water} and {DMC + 2-butanol + water}. The experimental ternary LLE data were correlated with the non-random two liquid (NRTL) and UNIversal QUAsiChemical (UNIQUAC) activity coefficient models. In addition, the Bachman–Brown correlation was used to ascertain the reliability of the experimental data for each system.     

Synthesis of yttrium titanate stannate (Y2Ti2−xSnxO7, x = 0–2) pyrochlore glass–ceramics as potential nuclear waste form

Y₂Ti_2−xSn_xO₇ (x = 0–2) pyrochlore sodium aluminoborosilicate glass–ceramics (GCs) are produced by calcining the pelletized Y–Ti–Sn oxide mixture and glass precursor at 1200 or 1300°C for 4 h. The metal oxide mixture is prepared by a soft chemistry route. X-ray diffraction, Raman spectroscopy, and electron microscopy are employed to investigate the formation of pyrochlore GCs and local crystal structures. Near phase pure Ti-rich pyrochlores are produced with minor phase SnO₂ observed for Sn-rich materials. The cell parameters of the pyrochlore structures refined by Le Bail fitting are in good agreement with the published data and increase linearly with the gradual increment of Sn substitution. With progressively increasing Sn proportion on pyrochlore B-site, Raman characteristic bands of the pyrochlore structure become sharper and well defined. The Raman A_1g peak position and its full width at half-maximum are linearly progressed with increasing x (Sn). The presence of the melting glass facilitates the pyrochlore formation, with ceramic grain sizes ranging from submicron to microns. Transmission electron microscopy and selected area electron diffraction observations indicate the sample possesses a relatively high crystallographic perfection at the atomic level. This new series of pyrochlore GCs and the method disclosed herein may pave the way for further materials development as potential nuclear waste forms.