http://nopr.niscair.res.in/handle/123456789/3124 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/3185 Title: Grain boundary scattering in silicon doped polycrystalline gallium nitride films prepared by rf sputtering <br/> <br/>Authors: Bhattacharyya, S R; Pal, A K <br/> <br/>Abstract: Silicon doped polycrystalline gallium nitride films have been deposited at temperatures ranging from 300 to 623 K on fused silica and silicon substrates by radio frequency sputtering technique. The films are characterized by optical measurements while the microstructural information is obtained from scanning electron microscopy and atomic force microscopy. X-ray photoelectron spectroscopy studies indicate compositional information in these films. The bonding environment in the film has been revealed from Fourier transformed infrared studies. Grain boundary parameters like density of trap states and barrier height are also evaluated. <br/> <br/>Page(s): 125-133 Thu, 29 Jan 2009 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/3184 Title: Temperature dependence of microwave loss in antiferroelectric squaric acid crystal <br/> <br/>Authors: Upadhyay, Trilok Chandra <br/> <br/>Abstract: A model of pseudospin for layers 1 and 2 of squaric acid (SQA) crystal proposed by Li and Qin, Ferroelectrics, 82 (1988), 69 has been modified to include pseudospin-phonon interaction and cubic and quartic phonon anharmonic interactions. With the help of double-time temperature dependent Green's function method and modified Hamiltonian, expressions for antiferroelectric soft mode frequency, dielectric constant and loss have been evaluated. By fitting model values of physical quantities in the theoretical expressions, temperature dependences of soft mode frequency and loss have been calculated. In the microwave frequency range, an increase in frequency is followed by increase in loss. The loss decreases with increase in temperature for SQA crystal in its paraelectric phase. This shows Curie-Weiss behaviour of the dielectric tangent loss. Theoretical results are compared with experimental results of Muser [Proc. 6th Int'l Meeting on Ferroelectricity, Kobe (1985)], Maier et al. [Phys Status Solidi (b) 89, (1978)], and Samara and Semmingsen [J Chem Phys 71 (3) (1979) 1401] which show a good agreement. <br/> <br/>Page(s): 119-124 Thu, 29 Jan 2009 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/3183 Title: Temperature dependence of microwave loss in rochelle salt crystal <br/> <br/>Authors: Upadhyay, Trilok Chandra; Kandpal, Balkrishna <br/> <br/>Abstract: Considering two-sublattice pseudospin lattice coupled mode model [Chaudhuri et al., J Phys Soc Jpn, 49(1980) 609] along with third-and fourth-order phonon anharmonic interaction terms and using double-time thermal Green's function method, expressions for shift, width, renormalized soft mode frequency, Curie temperature, dielectric constant and microwave absorption have been derived and discussed for rochelle salt crystal. By fitting model values of physical quantities, soft mode frequency, dielectric constant and microwave loss tangent have been calculated. Theoretical results compare well with experimental results of Sandy and Jones, Phys Rev, 168 (1968) 481. <br/> <br/>Page(s): 134-140 Thu, 29 Jan 2009 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/3181 Title: Ultrasonic investigation of amino acids in aqueous sodium acetate medium <br/> <br/>Authors: Thirumaran, S; Sabu, K Job <br/> <br/>Abstract: The ultrasonic velocity (U), density (ρ) and viscosity (η) measurements have been carried out for four amino acids namely L-alanine, L-leucine, L-valine and L-proline in aqueous sodium acetate solution as a function of composition at 303, 308 and 313K. Experimental data have been used to estimate the adiabatic compressibility (β), change in adiabatic compressibility (Δβ), relative change in adiabatic compressibility (Δβ/β₀), apparent molal compressibility (φĸ), apparent molal volume (φV), limiting apparent molal compressibility (φºK), limiting apparent molal volume (φºV) and the constants (S ĸ, SV), and viscosity B-coefficient. The results are discussed in terms of structure-making or structure-breaking effects of amino acids in the mixture. <br/> <br/>Page(s): 87-96 Thu, 29 Jan 2009 22:58:59 GMT