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The application scope of metal-organic frameworks (MOFs) can be extended by rationally designing the architecture and components of MOFs, which can be achieved via a metal-containing solid templated strategy. However, this strategy suffers from low efficiency and provides only one specific MOF from one template. Herein, we present a versatile templated strategy in which organic ligands are weaved into hydrogen-bonded organic frameworks (HOFs) for the controllable and scalable synthesis of MOF nanotubes. HOF nanowires assembled from benzene-1,3,5-tricarboxylic acid and melamine via a simple sonochemical approach serve as both the template and precursor to produce MOF nanotubes with varied metal compositions. Hybrid nanotubes containing nanometal crystals and N-doped graphene prepared through a carbonization process show that the optimized NiRuIr alloy@NG nanotube exhibits excellent electrocatalytic HER activity and durability in alkaline media, outperforming most reported catalysts. The strategy proposed here demonstrates a pioneering study of combination of HOF and MOF, which shows great potential in the design of other nanosized MOFs with various architectures and compositions for potential applications.

CuO–Ni/Al composites were synthesized by electroless deposition and thermal oxidation and characterized by inductively coupled plasma optical emission spectrometry, X-ray powder diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. Their performances as the heterogeneous catalysts for the solvent-free allylic oxidation of cyclohexene by oxygen were determined. It was found that the CuO contents and the amount of adsorbed oxygen species on the composites could significantly affect their catalytic performances in cyclohexene oxidation. The highest catalytic activity was achieved over CuO–Ni/Al-3 containing 18.5 wt% CuO with the highest amount of adsorbed oxygen species, which resulted in the maximum cyclohexene conversion of 39.1% and the total selectivity of 85.5% to 2-cyclohexene-1-ol, 2-cyclohexene-1-one, 2-cyclohexene-1-hydroperoxide and cyclohexene oxide. In addition, the catalyst was successfully recycled with no significant catalytic activity loss after three cycles.

Lattice thermal expansion (LTE) has been investigated in double perovskites LaPbMSbO6 (M = Mn, Co, Ni). Ordinary LTE behavior with good thermal stability is identified for the Mn sample, whereas unusual LTE with a preferably expanded interplanar distance of (040) is revealed for Co and Ni samples. Temperature-dependent X-ray diffraction patterns ( T-XRD), Raman spectra ( T-Raman), and specific heat capacities ( T- Cp) consistently indicate that a rare isostructural displacive phase transition (IDPT) with a second-order phase transition nature is predominant near the critical temperature. Refinements of neutron powder diffraction (NPD) and in situ T-XRD data present temperature-sensitive bond parameters which are relevant to planar oxygen O1. X-ray photoelectron spectra (XPS) further confirm the Jahn-Teller (J-T) activated Co2+ (HS) or Ni3+ (HS/LS) cations at the B-site sublattice. This unusual LTE behavior could be understood by the cooperative J-T effect contributed by a Pb2+ ion and Co2+/Ni3+ ion from A- and B-site sublattices, respectively. The importance of 6s(Pb)-2p(O)-3d(Co/Ni) extended orbital hybridization on affecting thermal expansion behavior is highlighted on the basis of temperature-induced phonon mode softening. This study presents a microscopic description of connection between anisotropic thermal expansion and a cooperative J-T effect, which inspired exploration of thermal-mechanical coupled functional materials based on LaPbMSbO6 double perovskites.

Microstructural stability is a crucial but controversial issue for Mg-Al-RE alloys. It is important to study the thermal stability of Al-RE intermetallic phase with individual RE element. In this work, Mg-4Al-4Nd-0.2Mn (AlNd44, wt%) alloy with individual RE element Nd was prepared by high-pressure die-casting (HPDC). The microstructure, microstructural stability and its effects on tensile properties and corrosion behavior were investigated. The results show that the HPDC AlNd44 alloy has two intermetallic phases, i.e., acicular Al 11 Nd 3 and particulate Al 2 Nd, which are distributed at grain/dendritic boundary regions and form reticular structure. According to the quantitative X-ray diffraction phase analysis, the content of Al 11 Nd 3 and Al 2 Nd phases is 2.5 wt% and 1.8 wt%, respectively. Both the two phases appear to be thermally stable at 473 K. While the acicular Al 11 Nd 3 phase has a tendency to decompose at temperature up to 573 K, and would decompose to particulate Al 2 Nd phase thoroughly at 673 K. Moreover, Al 2 Nd phase would also partly decompose at temperature above 573 K. The alloy in as-cast state, with an intermetallic skeleton at grain/dendritic boundary regions, exhibits relatively high tensile properties and corrosion resistance. In contrast, the alloy after annealing at 673 K has the worst tensile properties and corrosion resistance due to the obvious phase transition and microstructure change.

Al–Cu–Co alloys containing different intermetallic compound phases were fabricated by the arc-melting method and used as heterogeneous catalysts for solvent-free cyclohexane oxidation by oxygen. The element composition and bulk structure were characterized by ICP-OES, XRD, SEM, TEM and XPS. Co species were the major active component and a small amount of Cu dissolved in the Al13Co4 phase of the alloy exhibited a synergetic effect on improving the catalytic activity. Cu dissolved in the Al13Co4 phase, a decagonal quasicrystal approximant with a special atomic arrangement structure, could increase the electrical conductivity and accelerate electron transfer during the catalytic oxidation of cyclohexane, and thus improved the catalytic activity of the alloy. Among all the alloys prepared in the present work, the Al60Cu5Co35 alloy exhibited the best catalytic performance with a cyclohexane conversion of 6.4% and a total selectivity of 95.2% to cyclohexanol and cyclohexanone. No significant change in the catalytic activity of the Al60Cu5Co35 alloy was observed after five cycles.

A novel, green, and economic CaCO3 synthesis method using a CO2-storage material (CO2SM) was developed based on the strategy of carbon capture, utilization, and storage (CCUS). In this process, CO2SM was used as both a CO2 source and a crystal modifier to regulate and control the crystallization of CaCO3. 1,4-Butanediol (BDO) and/or 1,2-ethanediamine (EDA) from CO2SM played unexpected roles as a surfactant, structure-directing agent, and/or pH modulator. The effects of CO2SM concentrations, reaction temperatures, and reaction times were systematically investigated. Pure calcite (bundle-like and dumbbell-like) and pure vaterite (oblate spheroid and snowball-like) CaCO3 products were obtained. Moreover, the CO2SM was recycled to prepare same crystal phase CaCO3 upon the addition of an appropriate amount of Ca(OH)2 with 120 g·L–1 CO2SM concentration.

Lattice thermal expansion (LTE) has been investigated in double perovskites LaPbMSbO

A series of perovskite oxides SrBiMTiO6 (M = Fe, Mn, Cr) have been synthesized and characterized towards application as cathode materials for solid oxide fuel cells (SOFCs). X-ray diffraction (XRD) patterns reveal that all samples are stabilized in $$ \mathrm{Pm}\ \overline{3}\mathrm{m} $$ space group. Electrical conductivity, AC impedance characteristics, and thermal and chemical stability have been studied in order to assess their possible use as SOFC cathode materials. In comparison with other low electrical conductivity cathodes of SOFC, our results suggest that SrBiMnTiO6, which has the highest electrical conductivity (4.02 S cm−1) and moderate polarization resistance (0.104 Ω cm2) at 850 °C, is the most promising candidate among the three perovskite oxides for further study and optimization as a SOFC cathode material.

The synthesis, crystal structure, and dielectric properties of the titled compounds were described. The structural symmetry was determined to be monoclinic P 2 1 / n (No. 14) space group. Based on the highly ordered array of alternating MgO 6 and SbO 6 octahedra, these double perovskites exhibited significant octahedral tilting distortion according to the Glazer's notation system a − a − c + . As the result of substituting different rare earth ions from La 3+ to Nd 3+ , both the tolerance factor ( t ) and coordination number (CN) were reduced simultaneously and the B-site lattice distorted more heavily with the increase in chemical pressure by adopting smaller Ln 3+ ion. For the investigation of dielectric properties, all the samples consistently presented weak frequency dependent characteristic with relatively low dielectric constant ( e ') and low tangent loss (tan δ ). With the shrinkage of the Ln 3+ ion size, the corresponding e ' decreased remarkably and the dispersive tan δ peaks around 300 K shifted to low temperature, indicating that the space-charge-hopping mechanism dominated permittivity property can be tuned by controlling the degree of lattice distortion via substituting different Ln 3+ ions.

The B-site ordered double perovskite oxides LaPbMSbO6 (M=Co, Ni) have been synthesized via the modified Sol–Gel precursor two-step route. Rietveld refinements reveal strong abnormal structural distortion and BO6 octahedral deformation appearing along the ab plane. Owing to the cooperative Jahn–Teller effect of Co2+ and Pb2+ ions, the Co-related compound exhibits almost complete Co2+–Sb5+ order. For magnetic properties, spin-canted antiferromagnetic state with high extent of magnetic frustration is confirmed. The Ni-related compound presents heavier magnetic frustration for introducing tiny disorder on site occupation accompanied with valence state and further enhancing the complexity of magnetic competition. Dielectric measurements present a considerable temperature dependent dielectric relaxation with great dc-like loss feature in the LaPbCoSbO6. For LaPbNiSbO6, however, the permittivity with low dielectric loss is shown to be insensitive to either temperature or frequency. The corresponding electronic active energy manifests that the weakly bounded 3d-electron is prone to hop in a more distorted Co–Sb sublattice.

To date great efforts have been devoted to the development of solid oxide fuel cell (SOFC) devices that is able to run at intermediate temperature (IT) and to retain good electrochemical performance as in the high temperature regime. To this end, Tantalum (Ta) is doped into Sr 2 Fe 1.5 Mo 0.5− x Ta x O 6− δ (0.0 ≤ x ≤ 0.15) to further improve the electrochemical performance as the cathode materials for IT-SOFC. Pure orthorhombic Sr 2 Fe 1.5 Mo 0.5− x Ta x O 6− δ (0.0 ≤ x ≤ 0.15) samples, with space group Pnma (no. 62), are synthesized by a two-step method and identified via the powder X-ray Rietveld refinements. X-ray photoelectron spectroscopy and thermogravimetry results consistently show that the number of oxygen vacancy increases with the increasing of Ta content. The thermal expansion compatibility of the samples is found to match the electrolyte of La 0.9 Sr 0.4 Ga 0.1 Mg 0.2 O 3− δ (LSGM) better than that of cobalt-containing electrode compounds. Finally, the higher oxygen vacancy concentration leads to the enhanced ionic conductivity although electrical conductivity is slightly decreased due to the oxygen vacancy blocking. Therefore, Ta-doped Sr 2 Fe 1.5 Mo 0.5 O 6− δ is proved to be a promising candidate for future cathode materials of IT-SOFC.

An one-pot synthesis of aqueous ZnSe:Cu nanocrystals (NCs) is realized in aqueous solution by a facile yet efficient hydrothermal technique. The dopant emission spectrum of the NCs is tunable, spanning a wide range from 438 to 543 nm. Room-temperature quantum yield for the NCs prepared at the optimal conditions reaches as high as 20% without any post-treatment. The ZnSe:Cu NCs prepared in a neutral aqueous solution (pH=8) are remarkably stable and exhibit comparatively high photoluminescent quantum yield (PL QY) as high as 17%. First-principles pseudopotential calculations using plane-wave basis functions have been performed. The formation energies of copper ions occupied in the interstitial octahedron and substitutional tetrahedral Zn2+ sites have been calculated. The occupation of copper ions in the interstitial octahedral site is found to be more thermodynamics-facilitated by -0.98 eV. The density of state analysis indicates that the Cu-related emission is primary dominated by the substitutional tetrahedral Cu ions, and the large dopant related emission width of ZnSe:Cu NCs originated from the corresponding Cu 3d impurity band. (C) 2013 Elsevier B.V. All rights reserved.

A-site ordered double perovskites hold promise for potential device applications, where how their magnetic objects actually interact is known to influence functionality. Here, we investigate, by first-principles calculations, electronic and magnetic properties of YMn3Al4O12, and demonstrate that it is an antiferromagnetic insulator. Our calculations reveal the extended (Mn-O)-(O-Mn) superexchange as a primary magnetic coupling mechanism in YMn3Al4O12, and further identify the O-O bonds as a key factor to dominate coupling strength. We suggest that this superexchange mode is the origin of antiferromagnetic behavior, opening an additional avenue to understand magnetic coupling in A-site ordered double perovskites. (C) 2012 Elsevier Masson SAS. All rights reserved.

In order to optimize the electrical properties of co-doped ceria electrolytes, Ce0.8Ca0.15Sm0.05O2-delta (CCS) sintered at different temperatures (1150 degrees C, 1200 degrees C, 1250 degrees C, 1300 degrees C and 1350 degrees C for 8 h) have been prepared and systematically investigated. It is found that among these samples sintered at different conditions, the electrical conductivity (sigma) measured at 800 degrees C can be ranked as: CCS1250 degrees C: sigma(800 degrees C)(CCS1250 degrees C) = 2.38 x 10(-2) S cm(-1) > CCS1200 degrees C: sigma(800 degrees C)(CCS1200 degrees C) = 1.81 x 10(-2) S cm(-1) > CCS1150 degrees C: sigma(800 degrees C)(CCS1150 degrees C) = 1.50 x 10(-2) S cm(-1) > CCS1300 degrees C: sigma(800 degrees C)(CCS1300 degrees C) = 1.26 x 10(-2) S cm(-1) > CCS1350 degrees C: sigma(800 degrees C)(CCS1350 degrees C) = 0.68 x 10(-2) S cm(-1). The electrical conductivity of CCS increases with the increase of sintering temperatures, and the 1250 degrees C-sintered sample presents the highest conductivity because of the best microstructures. However, the electrical conductivity of CCS decreases when the sintering temperatures goes beyond 1250 degrees C. We attribute this to the phase instability. It reveals that microstructures and the phase stability have important effects on the optimization of electrical properties for the co-doped ceria electrolytes. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

A series of Bi-doped La2–xBixCoMnO6 double perovskite oxides are synthesized, and the impact of doping on crystal structures and magnetic properties is investigated comprehensively. X-ray photoelectron spectroscopy and Raman spectrum analyses reveal that ordering of Co and Mn ions at B-site is gradually improved with the rise of Bi concentration. Meanwhile, magnetic disordering is suppressed greatly by showing larger magnetic moments. Structurally, the Rietveld refinement shows that the bonds are elongated, while the bond angles are shrunken after doping, giving rise to lowered Curie temperature. We also observe a large negative zero-field-cooling magnetization, which is attributed to the formation of spin antiparallel or canted ferromagnetic domains and clusters that are separated by the antiphase boundaries. First-principles calculations confirm the enhanced Co–Mn ordering upon Bi doping by taking into account both the ordering and disordering configurations of La2CoMnO6, LaBiCoMnO6, and Bi2CoMnO6. More...

The effect of small addition of different sintering aids (MoO3 and WO3) on the electrical properties of Ce0.9Nd0.1O2−δ has been investigated. The (Ce0.9Nd0.1)1−xMxO2−δ (x = 0.0; M = Mo, W, x = 0.01; Ce0.9Nd0.1O2−δ: NDC, (Ce0.9Nd0.1)0.99Mo0.01O2−δ: NDCMo; (Ce0.9Nd0.1)0.99W0.01O2−δ: NDCW) solid solutions were prepared and characterized. The X-ray diffraction patterns indicate that all the samples are single phases with a cubic fluorite structure. Moreover, from the field-emission scanning electron microscopy results, it is found (Ce0.9Nd0.1)0.99M0.01O2−δ (M = Mo, W) sintered at 1300 °C for 15 h have better sinterability than Ce0.9Nd0.1O2−δ. The total conductivity ( σ t ) by electrochemical impedance spectroscopy are ranked as: NDCW ( σ t - NDCW 700 °C = 0.039 S cm − 1 ) > NDCMo ( σ t - NDCMo 700 ° C = 0.029 S cm − 1 ) > NDC ( σ t - NDC 700 ° C = 0.018 S cm − 1 ) measured at 700 °C, which is attributed to microstructures. It can be concluded that MoO3 and WO3 are both effective and WO3 seems to be more potential as sintering aids on the optimization of electrical properties for ceria-based electrolytes.

In order to identify competitive ion-conducting materials in ceria-carbonates composite electrolytes, M-NLCO (M = Ce0.8Sm0.2O2-δ (SDC), Ce0.8Gd0.2O2-δ (GDC), Ce0.8Y0.2O2-δ (YDC); NLCO = 0.53Li2CO3–0.47Na2CO3) sintered at different temperatures (600° C, 625° C, 650° C, 675° C and 700° C) have been prepared and characterized. It is found that independent of systems, the 675° C-sintered composites in M-NLCO always present the highest conductivities because of the best NLCO distribution and interfacial microstructures. Moreover, among three composites (sintered at 675° C), the total ( σ t ) and grain boundary ( σ g b ) conductivities measured at 600° C are ranked as: SDC-NLCO ( σ t − SDC - NLCO 600 ° C = 9.1 × 10 − 2 Scm − 1 , σ g b − SDC - NLCO 600 ° C = 28.1 × 10 − 2 Scm − 1 ) ﹥ GDC-NLCO ( σ t − GDC - NLCO 600 ° C = 5.8 × 10 − 2 Scm − 1 , σ g b − GDC - NLCO 600 ° C = 18.9 × 10 − 2 Scm − 1 ) ﹥ YDC-NLCO ( σ t − YDC - NLCO 600 ° C = 3.1 × 10 − 2 Scm − 1 , σ g b − YDC - NLCO 600 ° C = 12.6 × 10 − 2 Scm − 1 ), which is attributed to ionic-radius compatibility between the dopant and the host as well as the NLCO distribution and interfacial microstructures. It can be concluded that ionic-radius compatibility between the dopant and the host, NLCO distribution and interfacial microstructures have important effects on improving ionic conductivities for ceria-carbonates composite electrolytes.

LaMnO3+δ nanofibers have been prepared by electrospinning. The nearly 70% of Mn atoms is Mn4+, which is much higher than that in the nanoparticles. The average grain size of our fibers is approximately 20 nm, which is the critical size producing the nanoscale effect. The nanofibers exhibit a very broad magnetic transition with Tc≈255 K, and the Tc onset is around 310 K. The blocking temperature TB is 180 K. The sample shows weak ferromagnetic property above the TB and below Tc and superparamagnetic property near the Tc onset. The resistivity measurements show a metal-insulator transition near 210 K and an upturn at about 45 K.

A-site ordered double perovskites hold promise for potential device applications, where how their magnetic objects actually interact is known to influence functionality. Here, we investigate, by first-principles calculations, electronic and magnetic properties of YMn3Al4O12, and demonstrate that it is an antiferromagnetic insulator. Our calculations reveal the extended (Mn-O)-(O-Mn) superexchange as a primary magnetic coupling mechanism in YMn3Al4O12, and further identify the O-O bonds as a key factor to dominate coupling strength. We suggest that this superexchange mode is the origin of antiferromagnetic behavior, opening an additional avenue to understand magnetic coupling in A-site ordered double perovskites. (C) 2012 Elsevier Masson SAS. All rights reserved.

We have systematically investigated the electronic and magnetic properties of hypothesized A-site-ordered perovskite YMn₃Sc₄O₁₂ using first-principle calculation based on the density functional theory. Our calculated results predict that YMn₃Sc₄O₁₂ is both thermodynamically and mechanically stable and its ground state is antiferromagnetic insulator. The Mn(3+) is in the high-spin state. More importantly, by comparison to YMn₃Sc₄O₁₂, we point out that the empty Sc 3d orbital provides the Mn--O--Sc--O--Mn superexchange interaction, which is similar to its isostructural perovskite CaCu₃Ti₄O₁₂, and enhances the antiferromagnetic interaction between Mn ions. From these calculations, we can clearly see that the empty 3d orbital plays an important role to realize superexchange interaction.

The crystal structures, magnetic and dielectric properties for the ordered double perovskites LnPbNiSbO6 (Ln = La, Pr) have been investigated. Rietveld refinements of x-ray diffraction data have been indexed for the monoclinic symmetry in space group P21/n (No. 14) and a highly rock-salt ordered arrangement of NiO6 and SbO6 octahedra. The B-site lattices are distorted strongly due to the substitution of rare Earth ions at the A-site. The magnetization measurements show an antiferromagnetic ordering. The effective magnetic moments μ eff are larger than the spin-only values, suggesting that the orbital component for Ni2+ is significant. The maximum values of isothermal magnetization increase due to the lattice distortion of BO6 octahedra, which may weaken the antiferromagnetic interaction via Ni2+–O–Sb5+–O–Ni2+ paths. The dielectric constants for LaPbNiSbO6 present frequency dependence and the tan δ curves exhibit relaxor-like dielectric response. The e' decreases with the reduction of the magnetic moments of B-site transition metal ions, which reveals a relationship between the dielectric and magnetic properties.

The crystal structures, magnetic, and dielectric properties for the ordered double perovskites LnPbCoSbO6 (Ln = La, Pr, Nd) have been investigated. The crystal structure has been solved by Rietveld refinements of X-ray diffraction data in the monoclinic space group P21/n (No. 14). The Co2+ and Sb5+ ions are almost fully ordered over the B-site, and the octahedral framework displays significant tilting distortion according to the Glazer's tilt system a–a–c+. As the result of lanthanide contraction from La3+ to Nd3+, the B-site sublattice distortions become stronger accompanying with the reduction of the tolerance factor and coordination number. The magnetization measurements show an antiferromagnetic ordering with large effective magnetic moments (μeff) suggesting that the orbital component is significant. The maximum values of isothermal magnetization increase with the decrease in radii of rare earth ions, which is attributed to the weakening of antiferromagnetic interaction via Co2+–O–Sb5+–O–Co2+ paths. ...

We report the heat, magnetic, and dielectric properties of La2−xBixCoMnO6 with a series of Bi doping concentrations, focusing especially on the impact of A-site doping on B-site ordering. We demonstrate that the B-site ordering is enhanced via the Bi doping, resulting in a suppressed cluster-glass behavior, larger dielectric constant, and smaller tangent loss. Surprisingly, a pronounced step-like dielectric anomaly turns up near the spin-freezing temperature in the Bi-free oxide, which is suppressed significantly after Bi doping. We attribute the suppression of anomaly to the lessened amount of antisite defects at the B sites and the associated strengthened electronic localization.

Single-component electrolyte-free fuel cells possess a similar function to the traditional fuel cells with a complex three-component structure. However, how to enhance their electrical properties for practical industrial applications remains a timely and important issue. Here, we report the manipulation of concentration ratios of ionic to electronic conductors in an electrolyte-free Ce0.8Sm0.2O2-δ–Li0.15Ni0.45Zn0.4 by adjusting the relative weight between its two inside compositions. Our systematic investigations reveal that the fuel cell with 30% in weight of Li0.15Ni0.45Zn0.4 exhibits an almost uniform distribution of the two compositions and has a total conductivity as high as 10 × 10−2 S cm−1 at 600 °C. Such an enhancement is found to be attributed to the established balance between the numbers of its inside ionic and electronic conductors. These findings are relevant for the technological improvement of this new species of electrolyte-free fuel cell and represent an important step toward commercialization of this single-component fuel cell.