First principles lattice dynamical study of the cubic antiperovskite compounds AsNBa3 and SbNBa3

An ab initio pseudopotential plane wave method using linear response approach has been employed to study the lattice dynamics of two cubic antiperovskites AsNBa₃ and SbNBa₃. The bulk properties, elastic constants, phonon dispersion curves, phonon density of states and temperature dependent thermodynamic quantities of both antiperovskites are obtained. The calculated lattice constants, elastic and bulk properties are compared with the available theoretical data. This is the first systematic and quantitative prediction of phonon and thermodynamical properties of these antiperovskite compounds.     

Fine structure in the low temperature luminescence of Zn2SiO4:Mn and Mg4Ta2O9:Mn

The luminescence of powder samples of the well-known green-emitting Zn₂SiO₄:Mn and the red-emitting Mg₄Ta₂O₉:Mn phosphor shows a considerable fine structure at 4° K in appropriately prepared samples containing a sufficiently low Mn concentration. For (Zn_1-xMn_x)₂SiO₄ (0.0005?x?0.05) two sharp lines were found which are interpreted as due to zero phonon transitions between the ⁴T₁ and ⁶A₁ levels of Mn²⁺ ions on the two crystallographically different zinc sites. The remaining structure is ascribed to vibronic sidebands. The decay times of the luminescence bands associated with the two sites differ; they are 12 and 15 ms for the high and low energy bands respectively. The experimental results of Vlam are confirmed by our data. In addition some (Zn_1-yBe_y)₂SiO₄:Mn (0.025? y ?1) samples were investigated. In Mg₄Ta₂O₉:Mn two zero phonon lines could be identified, indicating that in this material Mn²⁺ is distributed over two inequivalent Mg sites. Most of the phonon replicas were found at intervals of 15 meV. Raman scattering experiments showed that this energy corresponds to one of the lattice vibrations. The decay time of this luminescence band is 1.0 ms.     

N-benzoate-N′ salicylaldehyde ethynelediamine: A new fluorescent sensor for Zn2+ ion by “off-on” mode

Imbalance of zinc ion (Zn²⁺) in human body causes diseases like Alzheimer’s and Parkinson’s and therefore Zn²⁺ estimation in biological fluids has diagnostic values. Fluorescence “off-on” sensors have advantages of high sensitivity and in situ application over other sensors. A new fluorescent “off-on” Zn²⁺ sensor, N-benzoate-N′ salicylaldehyde ethynelediamine (L), has been synthesisied. In 1:1(v/v) CH₃OH:PBS (PBS?=?phosphate buffer solution), L shows ca. 20 times enhancement in fluorescence intensity on interaction with Zn²⁺, due to snapping of photoinduced electron transfer (PET) process, which is selective over metal ions - Na⁺, K⁺, Ca²⁺, Ni²⁺, Cu²⁺, Cd²⁺, Hg²⁺ and Pb²⁺. These metal ions either individually or all together does not interfere the sensing ability of L towards Zn²⁺. A 1:1 interaction between L and Zn²⁺ ion with binding constant 10^4.25 has been established from spectroscopic data.     

Phonon dispersion in thorium: A pseudopotential approach

A one parameter model pseudopotential is used in investigating the phonon dispersion in thorium. A very good agreement has been obtained between theory and experiment, especially, in transverse branches. This is attributed to the removal of the discontinuity in the pseudopotential in r-space.     

The pure rotational spectrum of ZnCl (XΣ): Variations in zinc halide bonding

The radical ZnCl (X²Σ⁺) has been studied using millimeter-wave direct-absorption techniques. Pure rotational spectra of ⁶⁷Zn³⁵Cl, ⁶⁶Zn³⁷Cl, ⁶⁸Zn³⁵Cl, ⁶⁴Zn³⁵Cl, ⁶⁴Zn³⁷Cl, and ⁶⁶Zn³⁵Cl were measured in the vibrational ground state and data were also recorded for the latter three in the v = 1 and v = 2 states. Every rotational transition was found to be split into a doublet due to spin-rotation interactions. For ⁶⁷Zn³⁵Cl, each doublet exhibited additional splittings arising from hyperfine coupling of the ⁶⁷Zn (I = 5/2) nucleus. Rotational, fine structure, and hyperfine constants have been determined from these data, and equilibrium parameters calculated. The equilibrium bond length of ⁶⁴Zn³⁵Cl is found to be 2.13003305(24) Å, in good agreement with recent theoretical predictions. Interpretation of hyperfine constants indicates that the 12σ orbital is ∼70% Zn(4s) in character, suggesting that the zinc chloride bond is relatively ionic.     

Ultrasonic cavitation induced water in vegetable oil emulsion droplets--a simple and easy technique to synthesize manganese zinc ferrite nanocrystals with improved magnetization

In the present investigation, synthesis of manganese zinc ferrite (Mn_0.5Zn_0.5Fe₂O₄) nanoparticles with narrow size distribution have been prepared using ultrasound assisted emulsion (consisting of rapeseed oil as an oil phase and aqueous solution of Mn²⁺, Zn²⁺ and Fe²⁺ acetates) and evaporation processes. The as-prepared ferrite was nanocrystalline. In order to remove the small amount of oil present on the surface of the ferrite, it was subjected to heat treatment at 300 °C for 3 h. Both the as-prepared and heat treated ferrites have been characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), TGA/DTA, transmission electron microscopy (TEM) and energy dispersion X-ray spectroscopy (EDS) techniques. As-prepared ferrite is of 20 nm, whereas the heat treated ferrite shows the size of 33 nm. In addition, magnetic properties of the as-prepared as well as the heat treated ferrites have also been carried out and the results of which show that the spontaneous magnetization (σ_s) of the heat treated sample (24.1 emu/g) is significantly higher than that of the as-synthesized sample (1.81 emu/g). The key features of this method are avoiding (a) the cumbersome conditions that exist in the conventional methods; (b) usage of necessary additive components (stabilizers or surfactants, precipitants) and (c) calcination requirements. In addition, rapeseed oil as an oil phase has been used for the first time, replacing the toxic and troublesome organic nonpolar solvents. As a whole, this simple straightforward sonochemical approach results in more phase pure system with improved magnetization.     

Physical properties of the cubic spinel LiMn2O4

We have performed an ab initio study of structural, electronic, magnetic, vibrational and thermal properties of the cubic spinel LiMn₂O₄ by employing the density functional theory, the linear-response formalism, and the plane-wave pseudopotential method. An analysis of the electronic structure with the help of electronic density of states shows that the density of states at the Fermi level (N (E_F)) is found to be governed by the Mn 3d electrons with some contributions from the 2p states of O atoms. It is important to note that the contribution of Mn 3d states to N(_EF)$N\left(E_F\right)$ is as much as 85%. From our phonon calculations, we have obtained that the main contribution to phonon density of states (below 250 cm⁻¹) comes from the coupled motion of Mn and O atoms while phonon modes between 250 cm⁻¹ and 375 cm⁻¹ are characterized by the vibrations of all the three types of atoms. The contribution from Li increases rapidly at higher frequency (above 375 cm⁻¹) due to the light mass of this atom. Finally, the specific heat and the Debye temperature at 300 K are calculated to be 249.29 J/mol K and 820.80 K respectively.     

Mössbauer study of Zn2+ and Sn4+ additives in Nickel ferrites

The Mössbauer study of Fe⁵⁷ in polycrystalline solid solutions of Ni_{1 + x ? y}Zn_ySn_xFe_{2 ? 2x}O₄ (y = 0.1, 0.3, 0.5 and x = 0.1 to 0.5 with x varying in steps of 0.1) has been made. The present work has been aimed at investigating the variation of isomer shift, nuclear magnetic field at Fe⁵⁷ nuclei and ionic distribution at tetrahedral and octahedral sites when the concentration of Zn²⁺ and Sn²⁺ ions is successively increased in nickel ferrites. The ionic distribution in samples having low tin concentration has been explained on the basis of Neel's molecular field model whereas the ionic distribution of samples having high tin and zinc concentration has been explained on the basis of formation of isolated superparamagnetic clusters at the octahedral site. It has been inferred that a larger substitution of zinc and tin ions enhances relaxation effects.     

1H and 13C MAS NMR studies of light alkanes activation over MFI zeolite modified by Zn vapour

The early stages of methane, ethane and propane conversion were studied by in situ ¹H and ¹³C MAS NMR techniques over fully exchanged Zn²⁺/MFI catalyst obtained by the reaction with zinc vapour. The in situ techniques revealed strong interaction of alkanes with Zn²⁺ cations evidenced by significant shift of the corresponding NMR lines. Besides that, the formation of methyl zinc, ethyl zinc and n-propyl zinc species along with bridging and silanol surface OH-groups was detected already at the ambient temperature. These results pointed to dissociative adsorption of alkanes over (ZO)–Zn²⁺–(OZ) and (ZO)–Zn²⁺–(OSi) active sites of the catalyst. The dissociative adsorption was shown to be a dead-end surface reaction in the case of methane starting reactant, while in the case of ethane and propane, it appeared to be responsible for the initiation of the catalytic cycle leading to alkenes and dihydrogen formation and regeneration of zinc containing catalytic sites.     

Study of potassium-zinc borophosphate glasses

Potassium-zinc borophosphate glasses were prepared and studied in two compositional series xK₂O-(50−x)ZnO-10B₂O₃-40P₂O₅ and xK₂O-(50−x)ZnO-20B₂O₃-30P₂O₅ with x=0, 10, 20, 30, 40 and 50 mol% K₂O. The replacement of zinc by potassium decreases the density and increases the molar volume of these glasses, whereas glass transition temperature and chemical durability decrease with increasing potassium content. Structural changes were studied by ¹¹B and ³¹P MAS NMR and Raman spectroscopy. The observed changes in the spectra and the properties of the studied glasses can be ascribed to several reasons and namely to the differences in the space occupied by cations Zn²⁺ and 2K⁺, the differences in the electronegativity of zinc and potassium and a large difference in the field strength of Zn²⁺ and K⁺ cations and thus higher ionicity of K-O bonds in comparison with Zn-O bonds.     

First principles study on the structural,electronic and phonon properties of monolayer B2Si

Using first principles density functional theory, we predict a monolayer B₂Si structure with space group Pmm2 in the present work. This structure is confirmed to be dynamically stable. Based on the plane wave pseudopotential approach, the charge density, electron localization function, density of states, energy band, phonon property and thermal conductivity of Pmm2-B₂Si are systematically studied. It is interesting that the sp² hybridization and coordination bond of Si are found in Pmm2-B₂Si, which is the most important factor for its structural stability. The density of states and energy band analysis reveals that Pmm2-B₂Si is metallic because of the partial occupied Si 3pz and B 2pz states. Moreover, the acoustic-optical coupling is important for phonon transport in Pmm2-B₂Si, and the contribution of optical modes to the lattice thermal conductivity along the [100] and [010] directions is 13% and 12%, respectively. This study gives a fundamental understanding of the structural, electronic and phonon properties in Pmm2-B₂Si.     

Measurement of spin-alignment of excited12C2+ nuclei in interactions of16O with12C usingγ-decay in flight

Measuring energy spectra of nuclei afterγ-decay of excited states in flight the spin alignment of¹²C₂₊ states has been measured. Inelastic scattering,¹⁶O(¹⁶C,¹²C₂₊)¹⁶O and the reaction¹²C(¹⁶O,¹²C₂₊)¹⁶O leading to¹²C₂₊ (4.43 MeV) state have been studied. Characteristic line shapes of the¹²C₂₊ peak were observed using a Q3D magnetic spectrometer. The magnetic substate (m-states) population has been deduced from the spectra as function of reaction angle. A comparison of the measuredm-state population with reaction models shows that the first reaction is consistent with inelastic scattering although discrepancies remain. Discrepancies are also obtained if the reaction¹²C(¹⁶O,¹²C₂₊)¹⁶O is interpreted using a FRDWBA transfer calculation. At least 1/3 of the cross section can be attributed toα-transfer. A calculation which couples transfer and inelastic scattering channels seems to be necessary.     

Pressure dependence of the superconducting state parameters of metallic glass superconductor Mg70Zn30

Explicit expressions have been derived for the volume dependence of electron-phonon coupling strength (λ) and the Coulomb pseudopotential (μ^*) considering the variation of Fermi momentum (κ _F) and Debye temperature (θ _D) with volume. Ashcroft’s model pseudopotential and RPA form of dielectric screening have been used for obtaining pressure dependence of transition temperature (T _C) and the logarithmic volume derivative (Φ) of the effective interaction strength (N ₀ V) for metallic glass superconductor Mg₇₀Zn₃₀. It has been observed that T _C of the metallic glass Mg₇₀Zn₃₀ decreases rapidly with increase of pressure and the superconducting phase disappears at about 30% decrease of volume, for which the μ^* curve shows a minimum and an elbow is formed in the Φ graph.     

A pseudopotential calculation of the phonon spectrum of aluminium

The phonon dispersion curves for Al are calculated from a theory based on Coulomb interactions among the ions and a local pseudopotential interaction between ions and conduction electrons. Conduction electron correlations are taken into account according to a theory of Singwiet al. ^1,2. A dielectric constant is constructed which satisfies the compressibility sum rule. This is especially important for longitudinal phonons. The agreement of the computed frequencies with the experimental dispersion curves of Stedman and Nilsson³ is good. Sites, sizes and widths of Kohn anomalies in the dispersion curves are also calculated. As expected the theoretical curves show larger anomalies than the experimental data. Finally a comparison is made with the recent calculations of Wallace⁴.     

Mg2Sn电子结构及热力学性质的第一性原理计算

采用基于第一性原理的赝势平面波方法系统地计算了Mg₂Sn基态的电子结构、弹性常数和热力学性质.计算结果表明Mg₂Sn的禁带宽度为0.1198eV.运用线性响应方法确定了声子色散关系和态密度,得出Mg₂Sn的热力学性质如等容比热和德拜温度.计算Mg₂Sn的热导率并与实验数据相比较. 关键词： 第一性原理 电子结构 弹性常数 热力学性质     

Diluted ferromagnetic semiconductor (LaCa)(ZnMn)SbO isostructural to “1111” type iron pnictide superconductors

We report discovery of ferromagnetism in(LaCa)(ZnMn)SbO isostructural to the well-studied iron-based superconductor LaFeAs(O1 xFx).Spin is induced by partial substitution of Mn2+for Zn2+,while charge is induced by substitution of Ca2+for La3+within the parent compound LaZnSbO.Ferromagnetism with Curie temperature(TC)is observed up to 40 K at the spin doping 0.15 by introducing Mn2+into the Zn2+sites for(La0.95Ca0.05)(Zn1 xMnx)SbO.The Hall coefficient measurement indicates p-type carrier for(La0.95Ca0.05)(Zn0.9Mn0.1)SbO with concentration of n~1020cm 3showing anomalous Hall effect below TC.     

A new PET fluorescent sensor for Zn

A new Zn²⁺ fluorescent sensor NIDPA, with 1,8-naphthalimide as reporting group and di-2-picolylamine (DPA) as recognizing group, has been synthesized via simple steps. Based on photo-induced electron transfer (PET) mechanism, NIDPA has a five-fold fluorescent enhancement and 10 nm absorption blue-shift under simulated physiological conditions corresponding to the binding of Zn²⁺. Apparent dissociation constant for Zn²⁺ (K_d) is 0.83 nM, and Ca²⁺, Mg²⁺, Fe²⁺, Ni²⁺ and Cr³⁺have little influence on fluorescent enhancement. These results suggest that NIDPA can be used to quantitatively and selectively measure the concentration of Zn²⁺ around sub-nanomolar range.     

A Phenylbenzothiazole Derived Fluorescent Sensor for Zn(II) Recognition in Aqueous Solution Through “Turn-On” Excited-State Intramolecular Proton Transfer Emission

A highly selective and sensitive fluorescent Zn²⁺ sensor N-(2-(benzo[d]thiazol-2-yl)phenyl)-2-((pyridin-2-ylmethyl)amino)acetamide (1) that derived from 2-(2′-aminophenyl)benzothiazole has been developed. In aqueous solution (HEPES/CH₃CN=4/6, v/v, HEPES 20 mM, pH?=?7.4), sensor 1 displays highly selective recognition to Zn²⁺ over other metal ions with a distinct longer-wavelength emission enhancement. Sensor 1 binds Zn²⁺ through its amide form with a 1:1 binding stoichiometry, which switched on the excited-state intramolecular proton transfer (ESIPT). Graphical Abstract

A simple 2-(2′-aminophenyl)benzothiazole-based fluorescent “off-on” sensor for Zn²⁺ recognition in HEPES/CH₃CN(4/6, v/v, HEPES 20 mM, pH?=?7.4) solution through switching on ESIPT has been developed.     

Charge transfer effects on the luminescent properties of Eu3+ in oxysulfides

Energy shifts of 4f⁶ states of Eu³⁺ in matrices, and phonon sidebands, linewidths and luminescence decay of Eu³⁺ in Ln₂O₂S (Ln=Lu, Y, Gd and La) have been studied. The charge transfer state (CTS) of Eu³⁺ is described by a model in which a hole is transferred from Eu³⁺ to ligands. Septet states obtained from the 4f⁷(⁸S) + hole configuration of CTS interact with the ⁷F term of the 4f⁶ configuration. This effect causes downward shifts of ⁷F_J states in matrices. Diffuse charge distributions for ⁷F_J states due to the mixing with CTS make the curvatuve of their adiabatic potential curves be smaller than that for ⁵D_J'. Such a difference in the potential curves between ⁷F_J and ⁵D_J' causes broadening of the absorption lines compared with the corresponding emission linewidths in Y₂O₂S. A dynamic Jahn-Teller model is proposed for the concentration-enhanced phonon sidebands accompanying 4f-4f transitions. The vibronics appear only in the excitation spectra and not in the emission spectra. Spectral distributions of the effective density of phonon states are obtained from the observed phonon sidebands for Ln₂O₂S: 5%Eu. The phonon spectra indicate delocalization of the 4f orbitals of Eu³⁺ with increasing the host-cation radius. The observed lifetimes of ⁵D₀ show a decrease in the same order due to decrease in the 4f-CTS mixing.     

The magnetic moments of (vg 9/2)-levels in odd Zn isotopes

^69m,71mZn have been implanted with an isotope separator on-line into a cold iron host matrix. Nuclear magnetic resonance of the low-temperature oriented isotopes has been observed. The resonance frequencies for zero external magnetic field are v_L(^69mZnFe@#@) =36.814(35) MHz andv _L (^71mZnFe)=33.47(19) MHz. From these the magnetic moments of the 9/2⁺ iosmeric states have been derived as μ(^69mZn)=(?)1.138(18) n.m. andμ(^71mZn)=(?)1.035(18) n.m. The experimentally known magnetic moments of (vg _9/2)-levels in odd zinc isotopes are compared to theoretical estimates.