http://nopr.niscair.res.in/handle/123456789/2271 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/2317 Title: Melting temperatures of solids using the theory of equation of state <br/> <br/>Authors: Kumar, Manoj; Kumar, M <br/> <br/>Abstract: A simple method based on the theory of equation of state of solids is used to predict the melting temperatures of sixteen alkali halide solids. The results are compared with the experimental data. A good agreement between theory and experiment supports the validity of the model used. The method can also be used to determine B'օ when the melting temperatures are known. <br/> <br/>Page(s): 256-257 Mon, 26 Feb 2007 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/2316 Title: Dielectric and optical properties — Structure correlations in NiO doped Li₂O-MgO-B₂O₃ glasses <br/> <br/>Authors: Rao, R Balaji; Reddy, M Srinivasa; Reddy, P Yadagiri; Veeraiah, N <br/> <br/>Abstract: Glasses of the system, Li₂O-MgO-B₂O₃ containing different concentrations of NiO (ranging from 0 to 1.0 mol %) were prepared. A number of studies viz., dielectric properties (constant Ɛ, loss tan δ, ac conductivity σ ac over a range of frequency and temperature and dielectric breakdown strength) optical absorption, magnetic susceptibility and thermoluminescence on these glasses were carried out as a function of NiO concentration. An anomaly has been observed in all these properties when the concentration of NiO is about 0.6 mol % in the glass matrix. This has been explained in the light variation in the environment of Ni²⁺ ions in the glass network. <br/> <br/>Page(s): 243-255 Mon, 26 Feb 2007 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/2315 Title: Temperature dependent analysis of refractive index, band gap and recombination coefficient in nitride semiconductor lasers <br/> <br/>Authors: Gaikwad, S A; Samuel, E P; Patil, D S; Gautam, D K <br/> <br/>Abstract: Temperature dependent analysis of recombination coefficient, band gap and refractive index has been carried out to explore applicability of nitride lasers at higher temperatures. To estimate recombination coefficient at various temperatures Shockley-van Roosbroeck model has been used. Our results reveal that refractive index increases in linear manner with temperature and indium mole fraction in InGaN. However, refractive index was found to be decreasing with Al mole fraction and temperature in non-linear manner. The band gap deduced from our analysis was found to be increasing with Al mole fraction and decreasing with In mole fraction and therefore, these alloys provide better opportunity to form effective heterostructures with GaN. The recombination coefficient analysed, was observed to be decreasing non-linearly with band gap and temperature for AlGaN. However, in case of InGaN, the recombination coefficient shows linear increase with band gap and non-linear decrease with temperature. <br/> <br/>Page(s): 238-242 Mon, 26 Feb 2007 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/2314 Title: Structural and magnetic properties of zinc ferrite aluminates <br/> <br/>Authors: Lal, Roshan; Suman; Sharma, N D; Taneja, S P; Reddy, V R <br/> <br/>Abstract: Zinc ferrite aluminates ZnAlxFe₂₋xO₄ with composition (0≤ x ≤1) were synthesized at 1150C using the usual ceramic method and studied by X-ray diffraction, magnetization and Mössbauer measurements. It is observed that lattice parameter decreases, with increasing Al concentration (x). Mössbauer absorption spectra of all the samples recorded at room temperature showed three hyperfine magnetic sextets and a single quadrupole doublet. The outer sextet is assigned to ⍺- Fe₂O₃ crystalline phase, whereas inner two sextets refer to Fe³⁺ ions at octahedral (B) site and tetrahedral (A) site showing the formation of zinc ferrite aluminates phase. The hyperfine magnetic field was found to decrease with increasing Al concentration and has been explained on the basis of super transferred hyperfine field. The central doublet is partially dissociated forming ZnFeO₂ (delafossite) phase overlapping the main Mössbauer spectra measured at room temperature. The observed variations in saturation magnetization in all the samples have been explained on the basis of site distribution and the strength of the exchange interactions between the magnetic ions. On the basis of these observations, it is concluded that the present ferrite system exhibits a non-collinear magnetic structure with a very weak ferromagnetic character, which starts dominating further when zinc ferrite is diluted with non-magnetic Al³⁺ ions. <br/> <br/>Page(s): 231-237 Mon, 26 Feb 2007 22:58:59 GMT