http://nopr.niscair.res.in/handle/123456789/3428 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/3445 Title: Structural and dielectric behaviour of barium substituted lead zinc niobate <br/> <br/>Authors: Himanshu, A K; Gupta, D C; Dutta, Alo; Sinha, T P; Bandyopadhayay, S K <br/> <br/>Abstract: The polycrystalline samples of (Pb1xBax)(Zn1/3Nb2/3)O3 (PBZN) ceramics have been synthesized by the columbite precursor method. X-ray diffraction analysis of PBZN synthesized for x = 0.15, 0.25, 0.35 and 0.50 shows a cubic perovskite phase at room temperature. The changes in the structures are observed with increasing Ba contents in PBZN. The dielectric dispersion of the solid solutions has been studied as a function of temperature in the frequency range 100 Hz-1MHz. The temperature variation of the real components (ƐƐ) at different frequencies of the dielectric permittivity shows a broad maximum. The diffuse peaks in  versus T confirm the relaxor behaviour of PBZN. The changes in the relaxor properties of the compounds are found to be compositional dependent. The frequency dependence of Tm in these compounds with barium substitution is modeled using Vogel-Fulcher relation. <br/> <br/>Page(s): 212-219 Wed, 29 Oct 2008 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/3444 Title: Microstructure based model for effective thermal conductivity of snow <br/> <br/>Authors: Singh, Ashok K; Wasankar, K S <br/> <br/>Abstract: The paper presents a model to quantitatively relate macroscopic effective thermal conductivity (ETC) of snow with the microscopic interfacial contact area among the components using micro-structural parameters obtained from surface section images of snow samples. Unit cell model of Jackson and Black, based on stereological concept of contiguity, is expanded to include the effect of microstructure of snow, as well as, other parameters to predict the ETC of snow. The model is described by three dominant thermal conductance that account for the heat transfer across solid-solid, solid-liquid, and solid-air interface. The complex structure of snow is described using the primary microstructure parameters: coordination number, grain size, bond size, dendricity and sphericity. The ETC formulations developed, include the effect of these snow parameters besides the characteristics of the phases and temperature dependence of their conductivities. The model predictions agree closely with the measurements made using transient thermal probe method. The ETC values obtained from the present model are in close agreement with the observed values than the results of other existing models. <br/> <br/>Page(s): 206-211 Wed, 29 Oct 2008 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/3443 Title: Growth characterization and etching studies of calcium tartrate single crystal grown using tamarind extract <br/> <br/>Authors: Pradyumnan, P P; C, Shini <br/> <br/>Abstract: Calcium tartrate crystals were grown in silica gel by single diffusion method. The reactants used were calcium chloride and extract from tamarind juice. Crude as well as centrifuged tamarind extracts were used. The studies on the growth parameter of the crystal were conducted. The characterization studies such as XRD, FT-IR, TG-DTA of the grown crystals were done and it was then compared with that of calcium tartrate crystals grown using AR grade tartaric acid. The absorption spectral, CHN analysis and etching were also studied. <br/> <br/>Page(s): 199-205 Wed, 29 Oct 2008 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/3442 Title: ESR, IR, Raman and optical absorption studies of 60 B2O3 + 10 TeO2 +5TiO2 +24 R2O: 1CuO (where R=Li, Na, K) quaternary glasses <br/> <br/>Authors: Suresh, S; Prasad, M; Upender, G; Kamalaker, V; Mouli, V Chandra <br/> <br/>Abstract: ESR, IR, Raman and optical absorption spectra of 60 B2O3 + 10 TeO2 +5TiO2+24 R2O (where R = Li, Na and K) quaternary glasses containing Cu2+ spin probe have been studied. IR results show the BO3-BO4- ring structure interconnected by TeO3- and TeO4- groups, where the BO4- groups are neighbours of the TeO3-groups. BO3 → BO4 transition is also observed, which correlates with the conversion of TeO4 →TeO3. From Raman spectra, a weak band recorded at 805 cm-1 clearly indicates the presence of boroxol rings for potassium boro-tellurite glass alone. From ESR spectra, the three weak parallel components are observed in the low field region. However, the perpendicular components are not resolved leading to an intensive line in the high field region. When one kind of alkali oxide is replaced by another, the Spin Hamiltonian parameters have been found to vary drastically. The spin Hamiltonian parameter values indicate that the ground state of Cu2+ is dx2- y2 and the site symmetry around the Cu2+ ion is tetragonally distorted octahedral coordination. Optical absorption peak of Cu2+ is found to be a maximum at around 794 nm for Li2O containing borate rich glasses. This peak shifts towards the lower wavelength side as Li2O is replaced with Na2O, K2O. Bonding parameters indicate a slight covalency for the in-plane σ bonding as compared to in-plane and out-of-plane π bonds. <br/> <br/>Page(s): 163-169 Sat, 29 Oct 2005 22:58:59 GMT