电感耦合等离子体原子发射光谱法测定钛酸钡纳米粉体中7种杂质元素

钛酸钡纳米粉体样品用盐酸溶解,在所得样品溶液中用电感耦合等离子体原子发射光谱法测定了以氧化物存在于样品中的7种杂质元素(包括镁、锶、钾、钠、铝、硅及铁),对测定的光谱条件进行了试验并优化达到上述各元素的测定上限为0.1%(质量分数).测得方法的检出限(3S/b)为(单位μg·L-1):2.0(铝),1.0(铁),20.0(钾),0.2(镁),4.0(钠),3.0(硅)及0.5(锶).应用此方法分析了两件实样,所得结果的相对标准偏差(n=6)小于等于2.0%,对其中4种杂质元素(镁、钾、钠和锶)同时用HG/T 3587-1999标准中的方法作分析校核,所得结果与此方法结果一致.     

Peierls‐Distorted Monoclinic MnB4 with a MnMn Bond

Tetraborides of chromium and manganese exhibit an unusual boron‐atom framework that resembles the hypothetical tetragonal diamond. They are believed to be very hard. Single crystals of MnB₄ have now been grown. The compound crystallizes in the monoclinic crystal system (space group P2₁/c) with a structure that has four crystallographically independent boron‐atom positions, as confirmed by ¹¹B MAS‐NMR spectroscopy. An unexpected short distance between the Mn atoms suggests a double Mn–Mn bond and is caused by Peierls distortion. The structure was solved using group‐subgroup‐relationships. DFT calculations indicate Mn^I centers and paramagnetism, as confirmed by magnetic measurements. The density of states shows a pseudo‐band gap at the Fermi energy and semiconducting behavior was observed for MnB₄.     

Ordering double perovskite hydroxides by kinetically controlled aqueous hydrolysis

The precipitation of crystals with stoichiometric and ordered arrangements of distinct metal cations often requires carefully designed molecular precursors and/or sufficient activation energy in addition to the necessary mass transport. Here, we study the formation of ordered double perovskite hydroxides, MnSn(OH)(6) and CoSn(OH)(6), of the generic chemical formula, BB'(OH)(6) (no A site), using kinetic control of aqueous hydrolysis from simple metal salt solutions. We find that the precipitation yields ordered compounds only when the B ion is Mn(II) or Co(II), and not when it is any other divalent transition metal ion, or Zn(II). The key step in forming the compounds is the prevention of rapid and uncontrolled hydrolysis of Sn(IV), and this is achieved by a fluoride counteranion. The two compounds, MnSn(OH)(6) and CoSn(OH)(6), are studied by high-resolution synchrotron X-ray diffraction and from the temperature dependence of magnetic behavior. From maximum entropy image restoration of the electron density and from Rietveld analysis, the degree of octahedral distortion and tilting and the small extent of anti-site disorder are determined. From the nonoverlapping electron density, we infer strongly ionic character of bonding. As the first magnetic study of such materials, we report simple paramagnetic behavior with no long-range magnetic order down to 2 K for the Mn(II) compound, while the cobalt compound presents uncompensated antiferromagnetic interactions, attributed to the single-ion anisotropy of octahedral Co(II).     

Hybrid functional electronic structure of PbPdO?, a small-gap semiconductor

PbPdO?, a ternary compound containing the lone pair active ion Pb2? and the square planar d?Pd2? ion, has attracted recent interest because of the suggestion that its electronic structure, calculated within density functional theory using either the local density or the generalized gradient approximation, displays zero-gap behavior. In light of the potential ease of doping magnetic ions in this structure, it has been suggested that the introduction of spin, in conjunction with zero band gap, can result in unusual magnetic ground states and unusual magnetotransport. It is known that most electronic structure calculations do not properly obtain a band gap even for the simple oxide PdO, and instead obtain a metal or a zero-gap semiconductor. Here we present density functional calculations employing a screened hybrid functional which correctly obtain a band gap for the electronic structure of PdO. When employed to calculate the electronic ground state of PbPdO?, a band gap is again obtained, which is consistent with both the experimental data on this compound, as well as a consideration of valence states and of metal-oxygen connectivity in the crystal structure. We also present comparisons of the absolute positions (relative to the vacuum level) of the conduction band minima and the valence band maxima in α-PbO, PdO and PbPdO?, which suggest ease of p-type doping in PbPdO?, that has been observed even in nominally pure materials.     

Pd2+/Pd0 redox cycling in hexagonal YMn(0.5)Fe(0.5)O3: implications for catalysis by PGM-substituted complex oxides

Complex oxides--containing at least two different cations on crystallographically distinct sites--have recently been shown to display redox cycling of platinum group metals (PGMs), such as Pd; for example, Pd-substituted complex oxides can reversibly extrude metallic Pd under reducing conditions and then reincorporate Pd(2+) ions into the lattice under oxidizing conditions. The title compounds, YMn(0.5)Fe(0.5-x)Pd(x)O(3-δ) (0 ≤ x ≤ 0.07) crystallizing in the noncentrosymmetric YMnO(3) structure, were prepared using a sol-gel process at 800 °C, and the structures were refined from high-resolution synchrotron X-ray powder diffraction data. Their redox cycling behavior was monitored using synchrotron X-ray diffraction and EXAFS studies. In contrast to the previously studied complex oxide host compounds, YMn(0.5)Fe(0.5-x)Pd(x)O(3-δ) is only modestly tolerant to cycling: repeated redox cycling leads to the formation of PdO, which, on the time-scale of the oxidation cycles, does not reincorporate in the complex oxide lattice. Both oxidized and reduced samples were tested for the oxidation of CO to CO(2) under CO-lean conditions. YMn(0.5)Fe(0.5-x)Pd(x)O(3-δ) performs essentially as well as previously studied YFe(1-x)Pd(x)O(3-δ). The CO oxidation light-off characteristics of the hexagonal hosts are very similar to finely dispersed PdO. Despite evidence that Pd is almost fully dispersed as divalent ions in the host lattice, which is presumably accompanied by the concurrent creation of oxygen vacancies (2 Pd(2+):1 V(O(2-))), the as-prepared hexagonal materials do not display any significant improvement in catalytic activity as a function of Pd substitution level. This suggests that the corner-connected trigonal bipyramids that characterize this structural family do not enable the transport of oxygen through the bulk of the lattice. The study casts light on factors in the solid-state chemistry of precious metal-substituted complex oxides that influence the efficacy of redox cycling of the precious metal, and catalytic performance.     

Solitary wave solutions to nonlinear evolution equations in mathematical physics

This paper obtains solitons as well as other solutions to a few nonlinear evolution equations that appear in various areas of mathematical physics. The two analytical integrators that are applied to extract solutions are tan–cot method and functional variable approaches. The soliton solutions can be used in the further study of shallow water waves in (1+1) as well as (2+1) dimensions.