Investigations on the growth,optical behaviour and factor group of an NLO crystal: L‐alanine alaninium nitrate

Amino acid family crystals exhibit excellent nonlinear and electro‐optical properties. L‐alanine alaninium nitrate (LAAN) single crystal belonging to the amino acid group was grown by slow cooling solution growth technique. The High resolution X‐ray diffraction (HRXRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, UV‐Vis., Photoluminescence (PL) and Factor group analyses were carried out. The factor group analysis reveals 183 internal vibrations for the title compound. The second harmonic generation property was tested by Kurtz‐Perry powder technique. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth,dielectric and FIR reflectivity studies on PZN(0.91)‐PT(0.09) single crystals

Crystal growth of PZN‐PT single crystals using slow cooling flux technique with PbO flux is reported in this communication. Optimum growth conditions to maximize the amount of perovskite are also suggested. The grown crystals are characterized by dielectric and FIR spectroscopy. Temperature dependence of ε′ very close to the transition temperature shows a first order phase transition. Diffused phase transition and strong frequency dependence of ε′ around transition temperature are also observed. The real part of ε′ was found to obey the relation ε′ – ε_∞ = χ′(T‐T_o)². Dispersion in the ferroelectric phase is suggested to originate from ordering of domains. Competition in the B‐site occupancy by Zn, Nb and Ti ions is suggested to be the origin for the additional modes in the FIR reflectivity at room temperature. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of CdGeAs2 single crystals by a microprocessor-controlled bridgman system

A microprocessor-controlled Bridgman system was designed and fabricated for the growth of II-IV-V₂ compounds and one of this group of compounds CdGeAs₂ has been grown using a two-zone vertical Bridgman systein. The grown crystals have been characterized by X-ray and Hall effect.     

Thermal cycling,DLTS, and PEC studies on LEC gallium arsenide

This paper discusses the growth of gallium arsenide single crystals using the LEC technique. The Semi-insulating gallium arsenide was studied. The defect investigations were made by DLTS and etching studies. The variation of deep level concentration along the wafer was estimated using DLTS. The fabrication and efficiency of the PEC Solar cells are also reported.     

Growth and Characterisation of Pure and Nickel-doped Strontium Tartrate Tetrahydrate Single Crystals

Strontium tartrate tetrahydrate single crystals doped with nickel have been grown in silica gel. The grown crystals have been characterized by X-ray, atomic absorption spectroscopy (AAS), thermogravimetric analysis (TGA), and etching technique.     

Nanostructured metal particlemodified electrodes for electrocatalytic and sensor applications

Nanotechnology has become one of the most exciting frontier fields in analytical chemistry. The huge interest in nanomaterials, for example in chemical sensors and catalysis, is driven by their many desirable properties. Although metal is a poor catalyst in bulk form, nanometre-sized particles can exhibit excellent catalytic activity due to their relative high surface area-to-volume ratio and their interface-dominated properties, which significantly differ from those of the bulk material. The integration of metal nanoparticles into thin film of permselective membrane is particularly important for various applications, for example in biological sensing and in electrocatalysis. We have already established different techniques to design permselective membrane-coated chemically modified electrodes with incorporated redox molecules for electrocatalytic, electrochromic and sensor applications. Recently, we have prepared nanostructured platinum and copper (represented M_nano, M = Pt and Cu) modified GC/Nafion electrodes (GC/Nf/M_nano) and characterized by using AFM, XPS, XRD and electrochemical techniques. The nanostructured M_nano modified electrodes were utilized for efficient electrocatalytic selective oxidation of neurotransmitter molecules in the presence of interfering species such as ascorbic acid (AA) and uric acid (UA). It has been also shown that the modified electrodes could be used as sensors for the detection of submicromolar concentrations of biomolecules with practical applications to real samples such as blood plasma and dopamine hydrochloride injection solution. The GC/Cu_nano electrode has been used for catalytic reduction of oxygen.     

Infrared and raman studies on neodymium pentaphosphate and metaphosphates

The infrared and Raman spectra of crystalline samples of NdP₅O₁₄, NaNdP₄O₁₂ and KNdP₄O₁₂ are recorded. The spectra are analysed on the basis of vibrations of P=O, P-O, PO₂ and P-O-P groups. The P₄O ₁₂ ⁴⁻ ion has cyclic structures both in NaNdP₄O₁₂ and KNdP₄O₁₂ crystals. It has been inferred that the P-O-P bridges are stronger in metaphosphates.     

Iron(III) complexes of certain tetradentate phenolate ligands as functional models for catechol dioxygenases

Catechol 1,2-dioxygenase (CTD) and protocatechuate 3,4-dioxygenase (PCD) are bacterial non-heme iron enzymes, which catalyse the oxidative cleavage of catechols tocis, cis-muconic acids with the incorporation of molecular oxygen via a mechanism involving a high-spin ferric centre. The iron(III) complexes of tripodal phenolate ligands containing N₃O and N₂O₂ donor sets represent the metal binding region of the iron proteins. In our laboratory iron(III) complexes of mono- and bisphenolate ligands have been studied successfully as structural and functional models for the intradiol-cleaving catechol dioxygenase enzymes. The single crystal X-ray crystal structures of four of the complexes have been determined. One of thebis-phenolato complexes contains a FeN₂O₂Cl chromophore with a novel trigonal bipyramidal coordination geometry. The Fe-O-C bond angle of 136.1‡ observed for one of the iron(III) complex of a monophenolate ligand is very similar to that in the enzymes. The importance of the nearby sterically demanding coordinated -NMe₂ group has been established and implies similar stereochemical constraints from the other ligated amino acid moieties in the 3,4-PCD enzymes, the enzyme activity of which is traced to the difference in the equatorial and axial Fe-O(tyrosinate) bonds (Fe-O-C, 133, 148‡). The nature of heterocyclic rings of the ligands and the methyl substituents on them regulate the electronic spectral features, Fe^III/Fe^II redox potentials and catechol cleavage activity of the complexes. Upon interacting with catecholate anions, two catecholate to iron(III) charge transfer bands appear and the low energy band is similar to that of catechol dioxygenase-substrate complex. Four of the complexes catalyze the oxidative cleavage of H₂DBC by molecular oxygen to yield intradiol cleavage products. Remarkably, the more basic N-methylimidazole ring in one of the complexes facilitates the rate-determining productreleasing phase of the catalytic reaction. The present study provides support to the novel substrate activation mechanism proposed for the intradiol-cleavage enzymes.     

Density functional theory study on the structure and vibrational spectra for cyanuric chloride

The molecular structure and vibrational spectra of cyanuric chloride have been investigated by density functional theory (DFT) using standard B3LYP/6-31G* and B3LYP/6-311+G** method and basis set combinations. The DFT force field transformed to natural internal coordinates was corrected by a well-established set of scale factors that were found to be transferable to the title compound. Both the calculated structural parameters and vibrational frequencies are in good agreement with the available experimental data.