Dielectric and electrical properties of a tungsten bronze tantalate ceramic

Using high temperature solid state reaction the polycrystalline sample of K₂Pb₂Dy₂W₂Ti₄Ta₄O₃₀ was prepared. Single-phase compound formation was confirmed by preliminary X-ray structural analysis. The surface morphology recorded by scanning electron microscope at room temperature exhibits a dense uniform grain distribution on the surface of the sample. Ferroelectricity in the material is confirmed by the variation of polarization with temperature. The temperature and frequency dependence of electrical parameters (impedance, modulus, conductivity, etc.) of the material exhibits a strong correlation with its microstructure (i.e., bulk, grain boundary, etc.) and electrical properties. A typical Arrhenius behavior was observed in the temperature dependence of dc conductivity. The nature of frequency dependence of ac conductivity obeys Jonscher's universal power law. The variation of current with temperature shows that the material has high pyroelectric coefficient and figure of merit, thus making it useful for pyroelectric sensors with working temperature upto 500 °C.     

Synthesis,radiolabelling and biodistribution of HYNIC-Tyr<Superscript>3</Superscript> octreotide: a somatostatin receptor positive tumour imaging agent

In vivo imaging of tumours using radiolabelled somatostatin (SST) analogues has become an accepted clinical tool in oncology. HYNIC-Tyr³ octreotide and Tyr³ octreotide were synthesized by FMOC solid-phase peptide synthesis using a semi-automated synthesizer. These were analyzed and purified by RP-HPLC, mass spectroscopy, IR spectroscopy, ¹H NMR and ¹³C NMR. The prochelator 6-BOC-HYNIC was also synthesised and characterised indigenously. HYNIC-Tyr³ octreotide was labelled with ^99mTc using Tricine and EDDA as coligand by SnCl₂ method. Labelling with ^99mTc was performed at 100 °C for 15 min and radiochemical analysis by ITLC and HPLC methods. The radiochemical purity of the complex was over 98% and log p value was found to be −1.27 ± 0.12. The stability of radiolabelled peptide complex was checked at 37 °C up to 24 h. Blood clearance and protein-binding study was also performed. In vivo biodistribution studies in rat showed uptake of ^99mTc-HYNIC-TOC in kidney than any other organs. The blood clearance was faster with rapid excretion through kidneys and relatively low uptake in liver.     

Solubilization and stabilization of fullerene C60 in presence of poly(vinyl pyrrolidone) molecules in water

Solubilizing C₆₀ molecules in an aqueous medium is highly imperative in processing them in different forms of ionic or nonionic liquids, nanofluids, films and other derivatives. In this investigation, we report a facile chemical route using polymer molecules of poly(vinyl pyrrolidone) (PVP) which mediate C₆₀ molecules dissolving in water in a stable solution at room temperature. Poly(vinyl pyrrolidone) molecules, soluble in water as well as many organic liquids such as n-butanol, ethanol, or DMF, can be useful for transferring C₆₀ molecules from a non-aqueous to an aqueous system. A broad optical absorption arises over 270–520 nm when C₆₀ molecules are dissolved in water, 0.001–0.065 g/L in presence of 20–120 g/L PVP molecules. It consists of a strong π → π* absorption band (relatively sharp) lying at 294 nm in C(sp²) electrons from PVP-surface modified C₆₀ molecules followed by a broad charge transfer band which extends up to 520 nm. Upon a suitable surface modification, the C₆₀ molecules conquer enhanced optical absorption in both kinds of the bands. Dynamic light scattering reveals an average hydrodynamic length 181.5 nm and a polydispersity index 0.506 after a typical loading 0.065 g/L C₆₀. A zeta potential ?8.3 mV with a surface conductivity 0.064 mS/cm at 6.5 pH describes a negatively charged surface structure, showing an n-electron transfer from C=O (PVP) to a nanosurface in surface modified C₆₀ molecules in a weak donor–acceptor complex. Water soluble C₆₀ in presence of a biocompatible compound like PVP is useful for biological, medicinal, and other applications.     

Fascinating and challenging role of tungstate promoted vanadium phosphate towards solvent free esterification of oleic acid

A novel solid acid catalyst has been extensively used for the esterification reaction. Herein, tungstate promoted vanadium phosphate material is fabricated from its precursor, VOHPO(4)·0.5H(2)O and its catalytic activities and structure are investigated in detail. This kind of catalyst is, for the first time, applied for the effective production of biodiesel from fatty acids. Although vanadium phosphate has been extensively used in gas phase oxidation reactions, it has not drawn much attention for its application in liquid phase reactions. Our recent results indicate that vanadium phosphate is an effective, minimally polluting and re-usable catalyst that is highly suited to the production of biodiesel from fatty acids. This work extends the possibility of using VPO in other liquid phase reactions.     

Cluster Assembled Sb Films: Studies On Structure,Surface And Optical Properties

A low energy cluster beam deposition (LECBD) technique has been used to prepare the Sb cluster films on different substrates and are characterized using a variety of probes. Proton induced X-ray emission (PIXE) analysis shows the absence of any foreign trace elemental impurity even at ppm level. Glancing angle X-ray diffraction (GXRD) and transmission electron diffraction (TED) studies reveal the presence of single crystalline feature of Sb with hexagonal symmetry along with Sb-oxides. The transmission electron micrograph (TEM) of the cluster films of thickness 20 Å and 100 Å show size distribution which is more for the 100 Å film compared to that of the 20 Å one. The photoluminescence (PL) studies at 300 K show red shifted peaks along with the one possibly due to HOMO-LUMO transition around 2.4 eV. X-ray photoelectron spectroscopy (XPS) of Sb cluster films show shoulders to the core level peaks of the Sb corresponding to 3d 3/2 and 3d 5/2 which are shifted by 1.0 to 2.0 eV suggesting the formation of Sb-oxide. Raman scattering studies show the shift of A 1g and E g vibrational modes from their bulk value.     

Size distribution of magnetic iron oxide nanoparticles using Warren–Averbach XRD analysis

We use the Fourier transform based Warren–Averbach (WA) analysis to separate the contributions of X-ray diffraction (XRD) profile broadening due to crystallite size and microstrain for magnetic iron oxide nanoparticles. The profile shape of the column length distribution, obtained from WA analysis, is used to analyze the shape of the magnetic iron oxide nanoparticles. From the column length distribution, the crystallite size and its distribution are estimated for these nanoparticles which are compared with size distribution obtained from dynamic light scattering measurements. The crystallite size and size distribution of crystallites obtained from WA analysis are explained based on the experimental parameters employed in preparation of these magnetic iron oxide nanoparticles. The variation of volume weighted diameter (D_v, from WA analysis) with saturation magnetization (M_s) fits well to a core shell model wherein it is known that M_s=M_bulk(1?6g/D_v) with M_bulk as bulk magnetization of iron oxide and g as magnetic shell disorder thickness.     

Synthesis of nano ZnO thin film on Al foil by rf glow discharge plasma and its effect on E. coli and P. aeruginosa

Nano ZnO thin films were deposited on thin Al foils by a rf glow discharge plasma method in which sublimed zinc acetate vapor (precursor) reacted with oxygen plasma inside a low-pressure reactor. The films were microstructurally characterized using XRD, TEM, FESEM, optical reflectance and micro-Raman spectroscopy methods. In view of the good scope of ZnO coating in food packaging, the antibacterial activity in the ZnO thin films was studied by exposing the films to E. coli and P. aeruginosa for up to 8 h. Bacterial cell inhibition of up to 98–99 % was observed in the thin films.     

Microstructural analysis of neutron-irradiation induced changes in polyester fibre studied using EPMA

Electron microscopy is an important characterization technique for the study of textile fibre as it gives more information on fabric wear, nature of fibre fracture, chemical degradation, abrasion, fatigue and many others. Electron Probe Micro Analyzer (EPMA) micrographs of virgin and some neutron-irradiated samples (graphite coated) are discussed. The filament diameter, D, of virgin PET fibre obtained from EPMA study was 12.5 μn. The surface topography of single filament distinctly reveals the core and sheath parts of the filament. The core diameter of the virgin fibre was estimated to be 1.43 μm. The fibre irradiated at fluence 1 × 10¹² n/cm² shows radiation induced sphere like polymer balls or spherulites of diameter 2.27 μm in the expanded core region. Due to irradiation, the sheath area crosslinks with expanded core region, which may be responsible for increase of strength and hardness of the polymer materials. Moreover, the micrograph at 3000 X magnifications clearly shows that there is no preferred orientation of the polymer in any direction confirming the isotropic nature of the sample.      

Observation of grain growth in swift heavy ion irradiated NiO thin films

NiO thin films grown on Si(100) substrates by electron beam evaporation, were sintered at 500 °C and 700 °C. The films were irradiated with 120 MeV Au⁹⁺ ions. Irradiation had different effects depending upon the initial microstructure of the films. Irradiation of the films at a fluence of 3 × 10¹¹ ions cm⁻² leads to grain growth for the films sintered at 500 °C and grain fragmentation for the films sintered at 700 °C. At still higher fluences of irradiation, grain size in 500 °C sintered film decreased, but the same improved in 700 °C sintered film. Associated with the grain size, texturing of the films was also shown to undergo significant modifications under irradiation.     

Studies of dielectric and impedance properties of KCa2V5O15 ceramics

A polycrystalline sample, KCa₂V₅O₁₅, with tungsten bronze structure was prepared by a mixed-oxide method at low temperature (i.e., at 630 °C). A preliminary structural analysis of the compound showed an orthorhombic crystal structure at room temperature. Surface morphology of the compound was studied by scanning electron microscopy (SEM). Two dielectric anomalies at 131 and 275 °C were observed in the temperature dependency of dielectric response at various frequencies, which may be attributed to the ferroelastic-ferroelectric and ferroelectric-paraelectric transitions, respectively. The nature of variation of the electrical conductivity, and value of activation energy of different temperature regions, suggest that the conduction process is of mixed-type (i.e., ionic-polaronic and space charge generated from the oxygen ion vacancies). The impedance plots showed only bulk contributions, and non-Debye type of relaxation process occurs in the material. A hopping mechanism of electrical transport processes in the system is evident from the modulus analysis. The activation energy of the compound (calculated both from loss and modulus spectrum) is same, and hence the relaxation process may be attributed to the same type of charge carriers.