Vibrational properties and phase transitions in II-VI materials: lattice dynamics, ab initio studies and inelastic neutron scattering measurements

Inelastic neutron scattering measurements were carried out to determine the phonon density of states of ZnSe and interpreted with lattice dynamical computations (ab initio as well as a potential model). Calculations are also reported for other II-VI compounds, ZnTe and ZnS. Vibrational (phonon spectra and Grüneisen parameters), and thermal (negative thermal expansion and non-Debye specific heat) properties have been calculated and found to be in good agreement with available experimental data. This model has been further employed to study the pressure-induced solid-solid phase transitions exhibited by these compounds and the results have been compared with experimental data. Total energy calculations for zincblende and SC16 phases of ZnSe were carried out employing the pseudopotential approach under the local density approximation (LDA) as well as the generalized gradient approximation (GGA). The density functional perturbation theory is applied to study the vibrational properties of the zincblende and SC16 phases of ZnSe. An investigation of the pressure dependence of the phonon frequencies shows that the existence of the (experimentally undetected) SC16 phase as a thermodynamically stable high pressure phase is impeded due to dynamical instabilities. A detailed investigation of the polarization of phonons of different energies for the various phases of these compounds indicates that in the case of the zincblende phase the low energy modes are librational, while in the rocksalt phase the low energy modes are bending modes. Further, in ZnTe the low energy bending modes display a larger amplitude of bending than that in ZnSe and ZnS.     

Thin Layer Chromatographic Detection and Separation of Metal Ion Complexes with Tridentate Schiff Base

The Tridentate chelating, system present in Salicylidine o-amino benzoic acid was used for complexation with Cu (11), Ni (11), Co (11) and Pd (11). The thin-layer chromatographic (TLC) detection and separation of these complexes on Silica gel (G) layers was studied. The coloured spots of the complexes were quite visible without any visualizing agent. A maximum of four complexes could be resolved and identified. The coloured zones were eluted with solvent and characterise by elemental analysis and spectral studies. Colour of the complexes at λ_max was measured.     

Decomposition of an Fe-Cr 38 wt.% chromium stainless steel at 475 °C

The physical changes occurring at 475 °C in an Nb and Al stabilized stainless steel containing 38 wt.% Cr have been studied by Mössbauer spectroscopy. The specimen started to decompose when held at 475 °C. Decomposition still continues after 500 hours into a paramagnetic Cr-rich -phase and a nearly pure Fe -phase. The magnetic field distribution of the initial sample indicates that considerable decomposition has already taken place into an -phase with an estimated 15 at.% iron, and an iron-rich -phase with an estimated 18 at.% Cr.     

Synthesis and characterization of ambient temperature superionic solids in the composite system CuI–Ag<Subscript>2</Subscript>O–TeO<Subscript>2</Subscript>

The present work deals with the composite system (CuI) _x –(Ag₂O–TeO₂)_{100– x} , where x=30, 35, 40, 45, 50, 55, 60, 65, 70 and 75 mol%, respectively, synthesized by a solid-state reaction route. Powder specimens were analysed using differential scanning calorimetry, X-ray diffraction and Fourier transform infrared techniques. These studies have revealed the formation of Cu₃TeO₆, AgI and/or other phases. The ambient temperature electrical conductivities obtained for the samples using a complex impedance method were found to lie in the range 10^–6–10^–4 Scm^–1, with low activation energies, thus indicating their superionic nature. The typical composition 35CuI–32.5Ag₂O–32.5TeO₂ was identified as the best conducting one, having an electrical conductivity of 6×10^–4 Scm^–1 at 296 K and an activation energy of 0.23 eV. Ion transport number measurements carried out using Wagner's polarization technique as well as by an electromotive force method suggested that silver ions were responsible for the observed transport features of the composite system. Electronic Publication     

Aromatic and nitrogen-containing acid separation by reversed-phase high performance liquid chromatography and identification by photodiode array detector

A new method of separation and identification of aromatic and nitrogen-containing acids is presented. Fifty-seven different acid standards were separated by reversed-phase high performance liquid chromatography (HPLC). Detection and identification of the acids by ultraviolet (UV) spectra using a photodiode array detector (DAD) is demonstrated. Peak height ratios are reported and complete UV spectra of these acids are displayed. Possible applications of this technique are demonstrated using patients' urines.     

Synthesis and solid-state spectroscopic investigation of some novel diorganotin(IV) complexes of tetraazamacrocyclic ligands

The tetradendate macrocyclic ligands, [H₂L-1 = 5,12-dioxa-7,14-dimethyl-1,4,8,11-tetraazacyclotetradeca-1,8-diene] and [H₂L-2 = 6,14-dioxa-8,16-dimethyl-1,5,9,13-tetraazacyclohexadeca-1,9-diene] have been prepared by the condensation reaction of 1,2-diaminoethane and 1,3-diaminopropane, respectively, with ethyl acetoacetate in methanol at room temperature. The diorganotin(IV) complexes of general formula [R₂Sn(L-1)/R₂Sn(L-2)] (R = Me, n-Bu and Ph) have been synthesized by template condensation reaction of 1,2-diaminoethane or 1,3-diaminopropane and ethyl acetoacetate with R₂SnCl₂ (R = Me or Ph) or n-Bu₂SnO in 2:2:1 molar ratio at ambient temperature (35 ± 2 °C) in methanol. The solid-state characterization of resulting complexes have been carried out by elemental analysis, IR, recently developed DART-mass, solid-state ¹³C NMR, ^119mSn Mössbauer spectroscopic studies. These studies suggest that in all of the studied complexes, the macrocyclic ligands act as tetradentate coordinating through four nitrogen atoms giving a skew-trapezoidal bipyramidal environment around tin center. Since, the studied diorganotin(IV) macrocyclic complexes are insoluble in common organic solvents, hence good crystals could not be grown for single crystal X-ray crystallographic studies. Thermal studies of all of the studied complexes have also been carried out in the temperature range 0-1000 °C using TG, DTG and DTA techniques. The end product of pyrolysis is SnO₂ confirmed by XRD analysis.     

Surface waves propagating around the periphery of a piezoelectric cylinder of hexagonal symmetry with time dependent elastic stiffness

Acoustic surface waves propagating around the periphery of a piezoelectric cylinder of hexagonal symmetry are investigated. A co-axial structure with a piezoelectric insulator as the inner cylinder and electric conductor as the outer cylinder is considered. The dispersion equation is derived and solved under certain approximations assuming the elastic stiffness to be time dependent as in Voigt's model of viscoelasticity. The final expressions for the mechanical displacement component and electric potential are obtained. Ultimately some important parameters of such waves as group velocity, Poynting vector and power flow components have also been determined.I am grateful to Dr. A. K. Pal for his helpful suggestions in the preparation of the paper.     

Reactions of bis(cyclopentadienyl)titanium(IV) and zirconium(IV) chlorides with 1,1′-diacetylferrocenyl bis(hydrazones). Formation of trimetallic derivatives

Bis(cyclopentadienyl)titanium(IV) and zirconium(IV) chlorides react with bis(hydrazones) derived from 1,1-diacetylferrocene in anhydrous THF in the presence of base to give complexes of the type [(Cp₂MCl)₂L] [M = Ti or Zr; LH₂ = ferrocenyl bis(hydrazones)]. Tentative structures are proposed for these complexes based upon elemental analyses, electrical conductance, magnetic moment and spectroscopic data.     

A structural chemistry practitioner: a fox rather than a hedgehog. Reversibility of Friedel–Crafts acyl rearrangements

Structural Chemistry - A retrospective review of reversibility revealed in Friedel–Crafts acyl rearrangements of polycyclic aromatic ketones derived from the polycyclic aromatic hydrocarbons...