Growth and comparison of physicochemical properties of pure,Ca and Sr doped NH4Sb3F10 single crystals for electro optic applications

Single crystals of pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ are grown by slow evaporation technique. The effect of dopants on the growth and physicochemical properties also have been investigated and reported for the first time. The grown crystals are characterized with the aid of single crystal X-ray diffractometry to confirm the crystal structure. EDAX studies are done to confirm the presence of dopants in the crystal lattice. The vibrational frequencies of various group ligands in the crystals have been derived from the Fourier transform infrared (FT-IR) spectrum. From the optical absorption spectrum the band gap energy was calculated and it was found to be 5.76, 6.29 and 6.35 eV for pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ crystals respectively. Thermal stability of the sample has been analysed using TG-DTA analysis. The activation energy of pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ crystals were calculated from the dc conductivity measurements and it is found to be 0.2728, 0.2816 and 0.3622 eV Experimental results shows improved physicochemical properties when the dopant is added to the pure material.     

Electronic,mechanical, phase transition,and thermo-physical properties of TMC (TM = V,Nb, and Ta): high pressure ab initio study

The structural, electronic, mechanical, phase transition, and thermo-physical properties of refractory carbides, viz. VC, NbC, and TaC have been computed in stable B1 and high pressure B2 phases by means of two different ab initio calculations using pseudo- and full-potential schemes. These materials have mixed covalent-, metallic-, and ionic-type bonding. The calculations of elastic constants show the mechanical stability of these materials in B1 phase only. The brittle nature and anisotropy is observed in these materials in B1 phase. Non-central forces are present in both the phases. Elastic wave velocities and Debye temperature have also been calculated. The present results on structural, phase transition, elastic, and other properties are in reasonably good agreement with the available experimental and theoretical data. The calculations in high pressure phase need experimental verification.     

Facile preparation of mesoporous titanium nitride microspheres as novel adsorbent for trace Cd2+ removal from aqueous solution

A simple and facile route is developed for the preparation of mesoporous titanium nitride (TiN) microspheres with a large surface area and a highly porous structure. This method involves the preparation of an amorphous precursor via a solvothermal reaction and subsequent short-time nitridation process to mesoporous TiN. X-ray diffraction and X-ray photoelectron spectroscopy analyses confirm the composition of the resultant sample. The mesoporous structure of the as-prepared TiN sample has been studied by nitrogen adsorption/desorption measurement. The surface area obtained by the Brunauer–Emmett–Teller method is 50.6 m² g⁻¹ and the pore sizes are in the range of 2.0–4.0 nm. In addition, the obtained sample is evaluated as a new sorbent for Cd²⁺ removal. Experimental parameters such as solution pH, contact time and concentration of adsorbate are optimized. The maximum adsorption capacity for Cd²⁺ removal is found to be 12.40 mg g⁻¹ and it is a potentially attractive adsorbent for Cd²⁺ removal from aqueous solution.     

First principles study of the electronic structure and phonon dispersion of naphthalene under pressure

The structural, electronic and vibrational properties of crystalline naphthalene has been investigated within the framework of density functional theory including van der Waals interactions. The computed lattice parameters and cohesive energy have good agreement with experimental data. We study on the structural and electronic properties of the naphthalene under the hydrostatic pressure of 0–20 GPa. The isothermal equations of state calculated from the results show good agreement with experiment in the pressure intervals studied. The phonon dispersion curves have been computed at ambient and hydrostatic pressure of 10 and 20 GPa. We have also calculated the quasiparticle band structure of naphthalene with the G₀W₀ approximation.     

多孔建材中VOC扩散系数的两尺度模型

基于对建材微观结构的分析和压汞实验,提出了预测建材中有机挥发物(VOC)扩散系数的宏观一介观两尺度模型.和传统的从压汞实验计算扩散系数方法不同的是,本模型不仅考虑了孔隙率,还对孔的尺度分布和孔的连接方式进行了研究和分析.三种不同中密度板中VOC的散发实验表明,采用新模型计算的扩散系数比文献中的传统模型更好地吻合实验数据.     

Low-Temperature Anti-Stokes Luminescence in Zn1-xMgxSe Mixed Crystals

Investigations of photoluminescence and Raman scattering in the ternary Zn_1-xMg_xSe compounds at 4.2 K were performed both in the Stokes and anti-Stokes regions using cw laser excitation with various wavelengths within the transparency band of the crystals. The anti-Stokes luminescence was observed for the first time in the ternary Zn_1-xMg_xSe compounds. We have found variations in the shape and position of the Stokes and anti-Stokes luminescence bands with an increase in the band gap energy, which depends on magnesium content. We assume that the anti-Stokes emission is generated by two-step excitation via deep-level centers. It is shown that the low-temperature anti-Stokes photoluminescence can probe the spatial distribution profiles of impurities in the bulk of crystals.     

Thermodynamic modeling of Fe–Ni pentlandite

Gibbs energy modeling of iron–nickel pentlandite has been performed using experimental data of ternary phase equilibria. A three-sublattice approach in the framework of the Compound Energy Formalism is developed to refine a two-sublattice model of pentlandite recently applied within a complete assessment of the Fe–Ni–S system. Experimental data about the iron site fraction on the octahedral sublattice at 523.15 K for the composition Fe₅Ni₄S₈ as well as the enthalpy of formation at 298.15 K for the composition Fe_4.5Ni_4.5S₈ are predicted satisfactorily by the novel model. New possibilities to interpret experimental phase equilibrium data on complex phase relations with pentlandite are discussed together on the basis of the recent extension of a second high-temperature heazlewoodite phase to a ternary solution phase.     

A theoretical study of thiophenic compounds adsorption on cation-exchanged Y zeolites

A density functional theory (DFT) method has been applied to study the adsorption of thiophenic compounds such as thiophene (TP), benzothiophene (BT), dibenzothiophene (DBT) on cation-exchanged Cu(I)Y, Ni(II)Y, Ce(III)Y zeolites. All of calculations were carried out by the generalized gradient approximation (GGA) with the BLYP exchange-correlation functional and DNP basis set. The calculated results indicate that the stable adsorption configuration of TP molecule adsorbed on the Cu(I)Y is the η5 adsorption mode, whereas for BT and DBT, the η1S adsorption mode was found for the both molecules. Only the η1S adsorption mode can be obtained for the three thiophenic compounds adsorbed on the Ni(II)Y. The η5 adsorption mode can be ascribed to the adsorption of thiophene molecules on the Ce(III)Y, but the competition of different adsorption modes could possibly occur during the adsorption process of BT and DBT on the Ce(III)Y. Moreover, the selectivity of TP adsorbed on the adsorbents is in the order of Cu(I)Y > Ce(III)Y > Ni(II)Y, while for BT and DBT, the order is Cu(I)Y > Ni(II)Y > Ce(III)Y.     

Structural and short-range order analysis of glassy system

To understand the effects of structural features and to locate their signatures in the As-Ag-Te glassy system, various properties were studied as a function of average coordination number, 〈r〉. The structure of the sample is analyzed by X-ray diffraction technique and is found to be crystalline. The d-spacing and the lattice parameters of the samples were calculated. The structural parameters were discussed on the basis of Ag (silver) effect on As-Ag-Te glassy system. Structural investigations on these compositions revealed the polycrystalline nature of compositions with the presence of hexagonal As-Ag-Te phases. Grain size increased with the Ag content and parameters of unit cell are determined. The variations in the mean atomic volume, V, and the glass transition temperature, T_g, for glass transition, with composition have been reported. The change in thermal parameters was measured using differential thermal analysis (DTA). The results of the program are in agreement with those of analytical method and realized by binding energy represented by the cohesive energy values. The generalized ‘8-n’ rule was used to estimate the average coordination number. Obtained results were treated in the frame of chemical bond approach. We estimated some of physical parameters viz. mean bond energy, glass transition temperature, cohesive energy, average single bond energy, density, compactness and molar volume of all bulk samples. Our experimental and theoretical results were discussed in light of the topological bonding structure, which involves a hierarchy of correlation ranges in short-range order.     

Ab-initio calculations of electronic structure and optical properties of TiAl alloy

The electronic structures and optical properties of TiAl intermetallic alloy system are studied by the first-principle orthogonalized linear combination of atomic orbitals method. Results on the band structure, total and partial density of states, localization index, effective atomic charges, and optical conductivity are presented and discussed in detail. Total density of states spectra reveal that (near the Fermi level) the majority of the contribution is from Ti-3d states. The effective charge calculations show an average charge transfer of 0.52 electrons from Ti to Al in primitive cell calculations of TiAl alloy. On the other hand, calculations using supercell approach reveal an average charge transfer of 0.48 electrons from Ti to Al. The localization index calculations, of primitive cell as well as of supercell, show the presence of relatively localized states even above the Fermi level for this alloy. The calculated optical conductivity spectra of TiAl alloy are rich in structures, showing the highest peak at 5.73 eV for supercell calculations. Calculations of the imaginary part of the linear dielectric function show a prominent peak at 5.71 eV and a plateau in the range 1.1-3.5 eV.