http://nopr.niscair.res.in/handle/123456789/7411 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/7425 Title: Field dependent dielectric behaviour of Ba₁_-xCa_xTiO₃ferroelectric perovskites <br/> <br/>Authors: Pradeep, Dushyant; Kumar, Ashok; Naithani, U C <br/> <br/>Abstract: The electric field dependence of complex dielectric constant of Ba₁_-xCa_xTiO₃ferroelectric crystal in paraelectric phase has been studied by using the method of double times thermal Green’s function and Kubo formalism. A general expression is derived from the Silverman-Joseph Hamiltonian by taking into account the change of mass as well as harmonic force constant between impurity atom and host lattice atoms with fourth order phonon coordinates. The frequency, temperature and electric field dependent dielectric constant of Ba₁_-xCa_xTiO₃ crystal has been investigated. The dielectric constant increases with increase in temperature as well as with the applied electric field. The results are compared with the previous experimental and theoretical results. <br/> <br/>Page(s): 220-224 http://nopr.niscair.res.in/handle/123456789/7424 Title: Second law based performance of modified VAC hybrid heat pump system using NH₃-H₂O as the working fluid <br/> <br/>Authors: Tyagi, S K; Kim, M S; Park, S R; Anand, S <br/> <br/>Abstract: Vapour compression/absorption modified hybrid heat pump system using ammonia-water as the working fluid has been presented. The experimental as well as the theoretical performance based on the exergy analysis has been given. The irreversibility rate (exergy loss) in the low pressure compressor is found to be the highest while it is found to be the lowest in the case of expansion valve. It is also found that the irreversibility rate in low and high pressure compressors as well as the solution pump increase as the ambient air temperature increases. The effect of ambient air temperature is found to be more pronounced for the desorber while it is found to be reversed in the case of solution heat pump. <br/> <br/>Page(s): 212-219 http://nopr.niscair.res.in/handle/123456789/7423 Title: Study of structural, optical and transport properties of semiconducting Fe₂O₃-PbO-B₂O₃glasses <br/> <br/>Authors: Sanjay; Kishore, N; Agarwal, A <br/> <br/>Abstract: Semiconducting oxide glasses of compositions <i>x</i>Fe₂O₃.(40-<i>x</i>)PbO.60B₂O₃ have been prepared by the standard melt-quenching technique over the range 0 ≤ <i>x </i>≤ 20) (<i>x</i> is in mol%). The amorphous nature of the samples was ascertained using X-ray diffraction patterns. The structural changes in these glasses have been investigated by IR spectroscopy. The values of characteristic glass transition temperature (<i>T</i>_g) have been found from differential scanning calorimetry (DSC) traces and corresponding specific heat capacity (<i>C</i>_p) was also estimated. It is found that the density of these glasses decreases but glass transition temperature increases as Fe₂O₃ content is increased. The change in both the density and molar volume was discussed in terms of the structural modifications that take place in the glass matrix upon replacing PbO by Fe₂O_3.The <i>dc</i> conductivity of these samples was measured in the temperature range 473-623 K. In this temperature range, the <i>dc</i> conductivity increases from 10^-9 to 10^-4 S/m with increasing Fe₂O₃ content due to electron hopping from Fe(II) to Fe(III) ions. The values of the theoretical optical basicity of these glasses have also been determined. <br/> <br/>Page(s): 205-211 http://nopr.niscair.res.in/handle/123456789/7422 Title: Dielectric characterization of solution intercalation and melt intercalation poly(vinyl alcohol)-poly(vinyl pyrrolidone) blend-montmorillonite clay nanocomposite films <br/> <br/>Authors: Sengwa, R J; Sankhla, Sonu; Choudhary, Shobhna <br/> <br/>Abstract: Poly(vinyl alcohol) (PVA)-poly(vinyl pyrrolidone) (PVP) blend-montmorillonite (MMT) clay nanocomposite films up to 10 wt.% clay loading were synthesized by aqueous solution intercalation and melt compounding. Complex dielectric function, alternating current (<i style="">ac</i>) electrical conductivity and complex impedance of these films have been investigated as a function of clay concentration in the frequency range 20 Hz-1 MHz at 30°C. These films show significant decrease in the real part of relative dielectric function (<img src='/image/spc_char/italics_e.gif' border=0>') up to 3 wt. % MMT clay loading and at 5 wt.% their <img src='/image/spc_char/italics_e.gif' border=0>' values are found to be nearly equal to the PVA-PVP blend film. It is observed that the e¢ values of PVA-PVP blend-MMT clay films are lower than the PVA-MMT clay film at the same clay concentration. The <i style="">ac </i>electrical conductivity of these films increases with increase of frequency. The <i style="">dc</i> conductivity of these films varies anomalously with increase of clay concentration. The complex impedance spectra suggest that the dielectric properties of these nanocomposite films are independent of electrode polarization effect in the experimental frequency range. A correlation between dielectric function, structural ordering and the effect of preparation route were explored by considering clay intercalation and exfoliation and the interactions between polymer and MMT clay. This study revealed that the dielectric constant values of these organic-inorganic nanocomposite films can be tuned by loading MMT clay in the polymers matrix, which also improves their physical and thermal properties. <br/> <br/>Page(s): 196-204