Observation of Mixed Alkali Like Behaviour by Fluorine Ion in Mixed Alkali Oxyfluro Vanadate Glasses: Analysis from Conductivity Measurements

In this communication we report the fluorine ion dynamics in mixed alkali oxyfluro vanadate glasses. We have measured the electrical conductivity using impedance spectroscopy technique Room temperature conductivity falls to 5 orders of magnitude from its single alkali values at 33 mol% of rubidium concentration. We have also estimated the distance between similar mobile ions using the density values. Assuming this distance as the hopping distance between the similar ions we have estimated the anionic (Fluorine ion in our case) conductivity. It is observed that the fluorine ion dynamics mimics the mixed alkali effect and scales as the onset frequency f0.Comment: submitted to DAE-SSDP 2018 Indi

Nickel ferrite doped lithium substituted zinc and niobo vanadate glasses: thermal, physical, and electrical characterization

This study reports a comparison of some thermal, physical, and electrical properties of lithium substituted zinc and niobo vanadate glasses doped with nickel ferrite prepared for the electrical application. These glasses were prepared using the melt quenching technique. Density and differential scanning calorimetry were used to derive various physical and thermal properties. Packing density, the concentration of atoms, separations between atoms were compared between doped and undoped glass families. Thermal stability was estimated and compared. It is found that glasses with 20 mol% of Lithium are more stable than the rest. The thermal stability increases significantly by doping Nickel Ferrite from 5 °C to 30 °C in zinc vanadate glasses. Packing density varies with mol% of lithium ions from 0.43 to 0.42 in zinc vanadate glasses and from 0.40 to 0.42 in niobo vanadate glasses. Doping of Nickel ferrite varies the packing density from 0.42 to 0.43 in zinc vanadate glasses whereas it stabilizes the packing density to 0.42 in niobo vanadate glasses. Out of the two families of glasses, zinc vanadate glass doped with nickel ferrite shows better stability and higher packing density compared with others. DC electrical conductivities of the two families of glasses are almost similar and nickel ferrite doping has a little effect on DC electrical conductivity. Thus it is concluded that the nickel ferrite enhances the stability of the glass while maintaining DC electrical conductivity. This observation is important from the point of view of the electrical application of these glasses

Role of Crystal Field in Mixed Alkali Metal Effect: Electron Paramagnetic Resonance Study of Mixed Alkali Metal Oxyfluoro Vanadate Glasses

The mixed alkali metal effect is a long-standing problem in glasses. Electron paramagnetic resonance (EPR) is used by several researchers to study the mixed alkali metal effect, but a detailed analysis of the nearest neighbor environment of the glass former using spin-Hamiltonian parameters was elusive. In this study we have prepared a series of vanadate glasses having general formula (mol %) 40 V₂O₅–30BaF₂–(30 – <i>x</i>)­LiF–<i>x</i>RbF with <i>x</i> = 5, 10, 15, 20, 25, and 30. Spin-Hamiltonian parameters of V⁴⁺ ions were extracted by simulating and fitting to the experimental spectra using EasySpin. From the analysis of these parameters it is observed that the replacement of lithium ions by rubidium ions follows a “preferential substitution model”. Using this proposed model, we were able to account for the observed variation in the ratio of the <i>g</i> parameter, which goes through a maximum. This reflects an asymmetric to symmetric changeover of the alkali metal ion environment around the vanadium site. Further, this model also accounts for the variation in oxidation state of vanadium ion, which was confirmed from the variation in signal intensity of EPR spectra

Probing disorder and transport properties in polypyrrole thin-film devices by impedance and Raman spectroscopy

In the present study, impedance and Raman spectroscopy are adopted to probe the nature and extent of disorder to correlate with transport properties in doped polypyrrole (PPy) thin-film devices, synthesized electrochemically at different temperatures. A comparative study of the impedance spectroscopy is performed on PPy devices by both experimental and simulation approach with varying extent of disorder. The impedance measurements of PPy devices are well described by introducing a constant phase element (CPE) (Q) in modified RQ circuit, which accounts for frequency dependence of dielectric response. However, for the PPy grown at lower temperature, an equivalent circuit consisting of two such RQ elements in series is used for successful modelling of the impedance results, which accounts for the depletion region near the electrode. Raman spectroscopy and the de-convoluted spectra are successfully studied to probe the variation in C=C bond stretching and distribution of conjugation length, which relates to disorder in PPy films and the interpretation is well correlated to the impedance results

Association of Malassezia species with dandruff

Background & objectives: Malassezia species implicated with dandruff vary at different geographical locations. The present study was conducted to determine the spectrum and distribution of Malassezia species in dandruff patients and healthy individuals. Methods: Patients with dandruff from northern (Chandigarh) and southern (Manipal, Karnataka) parts of India (50 each) and healthy individuals (20) were included in the study. Dandruff severity was graded as mild, moderate and severe. Malassezia spp. isolated were quantified and identified by phenotypic characters and molecular methods including PCR-RFLP and DNA sequencing. Results: Number of Malassezia spp. retrieved was significantly higher (P<0.001) in dandruff cases (84%) as compared to healthy individuals (30%). Isolation of Malassezia spp. was significantly higher (P<0.01) in patients from southern India. In moderately severe cases M. restricta was single most predominant (37.8%) isolate from patients of northern part of India and M. furfur (46.4%) from patients of southern part of India. Malassezia density was significantly associated with the severity of dandruff (P<0.001). Interpretation & conclusions: Our results on a limited number of individuals show that Malassezia spp. associated with dandruff varies in different regions of the country and the density of yeasts increases with severity of disease