Band parameters of α-LiBeN semiconductor from density functional calculations

The structural, elastic, electronic, optical and thermal properties of α phase in LiBeN semiconductor have been studied using pseudo-potential plane wave method based on the density functional theory. The computed lattice parameter agrees well with previous theoretical work. The elastic constants and their pressure dependence are predicted using the static finite strain technique. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young’s modulus, Poisson’s ratio, average sound velocity and Debye temperature are numerically estimated in the frame work of the Voigt–Reuss–Hill approximation for α-LiBeN polycrystalline aggregate. The assignments of the structures in the optical spectra and band structure transitions have been examined and discussed. The thermal effect on heat capacities is investigated by the quasi-harmonic Debye model. To the best of our knowledge, most of the studied properties of the material of interest are reported for the first time.     

Further revisions on the diterpenoid alkaloids reported in a JNP paper (2012, 75, 1145–1159)

We have corrected (Tetrahedron2013, 69, 5859–5866) the structures of diterpenoid alkaloids reported in the Journal of Natural Products2012, 75, 1145–1159. Our follow-up experiments compel us to present further revisions and clarifications on the diterpenoid alkaloids:     

Lipase mediated separation of triterpene structural isomers, α- and β-amyrin

Pentacyclic triterpenoids α- and β-amyrin possess a wide range of biological and pharmacological activities. High structural similarity between these two structural isomers makes their chromatographic separation an ineffective and tedious choice. In this study, Candida rugosa lipase catalyzed separation protocol for the isolation of individual isomers has been developed. In the presence of vinyl acetate as the acyl donor, Candida rugosa lipase carried out acetylation of β-amyrin more efficiently as compared to α-amyrin leading to a kinetic separation. The conditions of transesterification reaction were optimized systematically, which was utilized to separate α- and β-amyrin from a mixture obtained from the latex of Plumeria obtusa.     

Structural phase transitions in Zn(CN)2 under high pressures

High pressure behavior of zinc cyanide (Zn(CN)₂) has been investigated with the help of synchrotron-based X-ray diffraction measurements. Our studies reveal that under pressure this compound undergoes phase transformations and the structures of the new phases depend on whether the pressure is hydrostatic or not. Under hydrostatic conditions, Zn(CN)₂ transforms from cubic to orthorhombic to cubic-II to amorphous phases. In contrast, the non-hydrostatic pressure conditions drive the ambient cubic phase to a partially disordered crystalline phase, which eventually evolves to a substantially disordered phase. The final disordered phase in the latter case is distinct from the amorphous phase observed under the hydrostatic pressures.     

Magnetic and structural properties of NaLnMnWO6 and NaLnMgWO6 perovskites

We have prepared 14 new AA′BB′O₆ perovskites which possess a rock salt ordering of the B-site cations and a layered ordering of the A-site cations. The compositions obtained are NaLnMnWO₆ (Ln=Ce, Pr, Sm, Gd, Dy, and Ho) and NaLnMgWO₆ (Ln=Ce, Pr, Sm, Eu, Gd, Tb, Dy, and Ho). The samples were structurally characterized by powder X-ray diffraction which has revealed metrically tetragonal lattice parameters for compositions with Ln=Ce, Pr and monoclinic symmetry for compositions with smaller lanthanides. Magnetic susceptibility vs. temperature measurements have found that all six NaLnMnWO₆ compounds undergo antiferromagnetic ordering at temperatures between 10 and 13 K. Several compounds show signs of a second magnetic phase transition. One sample, NaPrMnWO₆, appears to pass through at least three magnetic phase transitions within a narrow temperature range. All eight NaLnMgWO₆ compounds remain paramagnetic down to 2 K revealing that the ordering of the Ln³⁺ cations in the NaLnMnWO₆ compounds is induced by the ordering of the Mn²⁺ sub-lattice.     

Structural Transformation of Three‐Dimensional Bimetallic Phosphites Containing Corner‐Sharing 4‐Ring Chains

Two open‐framework bimetallic phosphites, [C₆H₁₈N₂][Co_0.3Zn_2.7 (HPO₃)₄] ( 1 ) and [C₂H₈N]₂[Co_0.3Zn_2.7(HPO₃)₄] ( 2 ) were synthesized and characterized. The inorganic frameworks of the two compounds are constructed from strictly alternating MO₄ (M = Zn, Co)tetrahedra and HPO₃ pseudo pyramids, forming three‐dimensional networks with 8‐ring and 12‐ring channels for 1 and 16‐ring channels for 2 . The anionic frameworks of the two compounds can be easily transformed to a neutral framework structure with 16‐ring channels at room temperature.     

Structural stability and robustness to bounded rationality for non-compact cases

We study the model M consisting of “general games” with noncompact action space, together with an associated abstract rationality function. We prove that M is structurally stable and robust to ϵ-equilibria for “almost all” parameters. As applications, we investigate structural stability and robustness to bounded rationality for noncooperative games, multiobjective optimizations and fixed point problems satisfying existence and some continuity conditions. Specifically, we introduce concrete rationality functions for such three kinds of problems with both payoffs and strategy sets, objective functions and domain spaces, and correspondence and domain spaces as parameters, respectively, and show the generic structural stability and robustness to bounded rationality for the corresponding model Ms.     

Microwave synthesis and phase transitions in nanoscale BiFeO<Subscript>3</Subscript>

Nanosized multiferroic BiFeO₃ powders were synthesized by a microwave combustion method. The average crystallite sizes of the samples stay at a same level with the ratio of fuel glycine 0.5 ≤ G/N ≤ 1.5 and it increases significantly with G/N = 2.0. An inhomogeneity of amorphous and microcrystallites is observed directly by HRTEM. A ferromagnetic hysteresis loop with a saturation magnetization (M _S) of ~0.09 μ _B /Fe has been observed at room temperature in the sample with a crystallite size of 53 nm, whereas other powders with much smaller crystallite size (~20 nm) will not saturate even at 20 kOe. These magnetic behaviors were ascribed to a combination of the magnetic enhancement effect of a decreased crystallite size and superparamagnetic mechanism.     

Micro-Raman investigations of mixed gas hydrates

We report laser Raman spectroscopic measurements on mixed hydrates (clathrates), with guest molecules tetrahydrofuran (THF) and methane (CH₄), at ambient pressure and at temperatures from 175 to 280 K. Gas hydrates were synthesized with different concentrations of THF ranging from 5.88 to 1.46 mol%. In all cases THF molecules occupied the large cages of sII hydrate. The present studies demonstrate formation of sII clathrates with CH₄ molecules occupying unfilled cages for concentrations of THF ranging from 5.88 to 2.95 mol%. The Raman spectral signature of hydrates with 1.46 mol% THF are distinctly different; hydrate growth was non-uniform and structural transformation occurred from sII to sI prior to clathrate melting.     

Ag nanoparticles deposited onto silica,titania, and zirconia mesoporous films synthesized by sol–gel template method

A variety of Ag nanoparticles/oxide mesoporous films with templated silica, titania, and zirconia was synthesized by sol–gel method at glass, aluminum, and silicon substrates using metal alkoxides (tetraethoxysilane, titanium tetraisopropoxide, and zirconium tetrapropoxide) and AgNO₃ as precursors of oxide films and Ag nanoparticles, respectively, and Pluronic P123 as a template agent. Oxide films alone and Ag/oxide composites were characterized using hexane adsorption, X-ray diffraction (XRD), Raman and ultraviolet (UV)/vis spectroscopies, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods. The distribution of Ag nanoparticles within the films, their sizes, intensity, and position of surface plasmon resonance (SPR) absorbance band at λ = 400 nm, as well as the textural and structural characteristics of whole films depend on treatment temperature, types of substrates and oxide matrices, oxide crystallization, and Ag content. Ag nanoparticles form preferably on the outer surface of the films under lower sintering temperatures if the amount of loaded silver is low. Oxide crystallization (e.g., TiO₂) promotes silver embedding into the outer film layer. At higher silver content (≥10 at.%) and higher calcination temperature (873 K), silver nanoparticles could be entrapped more uniformly along the film profile because of more intensive evaporation of silver droplets from the outer surface of the films on heating.