Crystal chemistry and stability of "Li7La3Zr2O12" garnet: a fast lithium-ion conductor

Recent research has shown that certain Li-oxide garnets with high mechanical, thermal, chemical, and electrochemical stability are excellent fast Li-ion conductors. However, the detailed crystal chemistry of Li-oxide garnets is not well understood, nor is the relationship between crystal chemistry and conduction behavior. An investigation was undertaken to understand the crystal chemical and structural properties, as well as the stability relations, of Li(7)La(3)Zr(2)O(12) garnet, which is the best conducting Li-oxide garnet discovered to date. Two different sintering methods produced Li-oxide garnet but with slightly different compositions and different grain sizes. The first sintering method, involving ceramic crucibles in initial synthesis steps and later sealed Pt capsules, produced single crystals up to roughly 100 μm in size. Electron microprobe and laser ablation inductively coupled plasma mass spectrometry (ICP-MS) measurements show small amounts of Al in the garnet, probably originating from the crucibles. The crystal structure of this phase was determined using X-ray single-crystal diffraction every 100 K from 100 K up to 500 K. The crystals are cubic with space group Ia3?d at all temperatures. The atomic displacement parameters and Li-site occupancies were measured. Li atoms could be located on at least two structural sites that are partially occupied, while other Li atoms in the structure appear to be delocalized. (27)Al NMR spectra show two main resonances that are interpreted as indicating that minor Al occurs on the two different Li sites. Li NMR spectra show a single narrow resonance at 1.2-1.3 ppm indicating fast Li-ion diffusion at room temperature. The chemical shift value indicates that the Li atoms spend most of their time at the tetrahedrally coordinated C (24d) site. The second synthesis method, using solely Pt crucibles during sintering, produced fine-grained Li(7)La(3)Zr(2)O(12) crystals. This material was studied by X-ray powder diffraction at different temperatures between 25 and 200 °C. This phase is tetragonal at room temperature and undergoes a phase transition to a cubic phase between 100 and 150 °C. Cubic "Li(7)La(3)Zr(2)O(12)" may be stabilized at ambient conditions relative to its slightly less conducting tetragonal modification via small amounts of Al(3+). Several crystal chemical properties appear to promote the high Li-ion conductivity in cubic Al-containing Li(7)La(3)Zr(2)O(12). They are (i) isotropic three-dimensional Li-diffusion pathways, (ii) closely spaced Li sites and Li delocalization that allow for easy and fast Li diffusion, and (iii) low occupancies at the Li sites, which may also be enhanced by the heterovalent substitution Al(3+) ? 3Li.     

Asymmetric integral as a limit of generated Choquet integrals based on absolutely monotone real set functions

We introduce a generated Choquet integral with respect to absolutely monotone and sign stable set functions. Another type of integrals defined with respect to such a set function is obtained as a limit of an appropriate sequence of generated Choquet integrals.     

One-step 9-stage Hermite–Birkhoff–Taylor ODE solver of order 10

A one-step 9-stage Hermite–Birkhoff–Taylor method of order 10, denoted by HBT(10)9, is constructed for solving nonstiff systems of first-order differential equations of the form y′=f(x,y), y(x ₀)=y ₀. The method uses y′ and higher derivatives y ⁽²⁾ to y ⁽⁴⁾ as in Taylor methods and is combined with a 9-stage Runge–Kutta method. Forcing a Taylor expansion of the numerical solution to agree with an expansion of the true solution leads to Taylor- and Runge–Kutta-type order conditions which are reorganized into Vandermonde-type linear systems whose solutions are the coefficients of the method. The new method has a larger scaled interval of absolute stability than Dormand–Prince DP(8,7)13M. The stepsize is controlled by means of y ⁽²⁾ and y ⁽⁴⁾. HBT(10)9 is superior to DP(8,7)13M and Taylor method of order 10 in solving several problems often used to test high-order ODE solvers on the basis of the number of steps, CPU time, and maximum global error. These numerical results show the benefits of adding high-order derivatives to Runge–Kutta methods.     

Synthesis of new antimicrobial 4-aminosubstituted 3-nitrocoumarins

A series of new coumarin derivatives has been synthesized by condensation of 4-chloro-3-nitrocoumarin and the appropriate arylamine and sulfonamide in ethyl acetate in the presence of triethylamine. The synthesized compounds were screened for their in vitro antimicrobial activity against thirteen strains of bacteria and three fungal/yeast strains using disk diffusion assays. They were shown to possess a wide range of activities from almost completely inactive compounds to medium active ones. (4-[(5-Chloropyridin-2-yl)amino]-3-nitro-2H-chromen-2-one) showed similar activity against Klebsiella pneumoniae as tetracycline.     

Direct Zinc Finger Protein Persulfidation by H2S Is Facilitated by Zn2+

H₂S is a gaseous signaling molecule that modifies cysteine residues in proteins to form persulfides (P‐SSH). One family of proteins modified by H₂S are zinc finger (ZF) proteins, which contain multiple zinc‐coordinating cysteine residues. Herein, we report the reactivity of H₂S with a ZF protein called tristetraprolin (TTP). Rapid persulfidation leading to complete thiol oxidation of TTP mediated by H₂S was observed by low‐temperature ESI‐MS and fluorescence spectroscopy. Persulfidation of TTP required O₂ , which reacts with H₂S to form superoxide, as detected by ESI‐MS, a hydroethidine fluorescence assay, and EPR spin trapping. H₂S was observed to inhibit TTP function (binding to TNFα mRNA) by an in vitro fluorescence anisotropy assay and to modulate TNFα in vivo. H₂S was unreactive towards TTP when the protein was bound to RNA, thus suggesting a protective effect of RNA.     

The H+NO recombination reaction over a wide temperature range

Rate coefficients of the title reaction have been measured in a high‐temperature photochemistry (HTP) reactor using Ar as the bath gas. H atoms were generated by flash photolysis of NH₃ and their relative concentrations were monitored by resonance fluorescence. The data are best fitted by k(295–905 K) = 6.5 × 10^?34 (T/K)^0.206 exp(780K T) cm⁶ molecule^?2 s^?1, with ±2σ precision values varying from 16 to 36% and corresponding suggested accuracy levels of 29–42%. Using a literature value for the relative collision efficiencies of N₂ and Ar indicates that for N₂ as the third body the above rate coefficient expression should be multiplied by 1.6. This leads to good agreement with two recent near 1000 K measurements. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 374–380, 2003     

Rapid spectrophotometric determination of cobalt with 2,2'-dipyridyl ketoxime

A rapid spectrophotometric method for the determination of low levels of cobalt(III) with 2,2 -dipyridyl ketoxime is proposed. A 3:1 water-soluble complex which is easily extractable into chloroform and has an absorption maximum at 388 mmicro forms instantaneously. Beer's law is obeyed and the molar absorptivity is 19.5 x 10(3). An investigation of the interference of 60 cations and anions shows the method to be widely applicable; it is simple, convenient and reproducible.