http://nopr.niscair.res.in/handle/123456789/8746 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/8862 Title: Effective charges in ternary chalcogenide spinels <br/> <br/>Authors: Kushwaha, A K; Kushwaha, S S <br/> <br/>Abstract: The effective ionic charge <i style="">Z*e</i> of each ion is determined within a narrow variable range for ternary chalcogenide spinel compounds. The Szigeti effective charge <i style="">e*</i>_s is also evaluated for the anion and cation using the observed optical dielectric constant Ɛ_ω. The correlation between <i style="">e*</i>_s and the dielectric constant Ɛ_ω are empirically found as Ɛ_ω-1=2.0/[(<i style="">e*</i>_s./<i style="">Z</i>_eff<i style="">e</i>)+(<i style="">e*</i>_s./<i style="">Z</i>_eff<i style="">e</i>)²].From effective ionic charges, we conclude that the ionicity increases in the order oxide > sulphide > selenide, indium compounds > chromium compounds, normal spinel > inverse spinel. <br/> <br/>Page(s): 664-667 Mon, 29 Aug 2005 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/8861 Title: Temperature dependence of lattice energy of fluorite type AB₂ crystals, alkaline earth oxides and heavy metal halides – Evaluation from sound velocity data <br/> <br/>Authors: Subrahmanyam, M; Rajagopal, E; Murthy, N Manohara <br/> <br/>Abstract: Lattice energies of CaF₂, SrF₂, BaF₂, CdF₂, EuF₂, MgO, SrCl, AgCl and TlBr at different temperatures have been evaluated making use of single crystal elastic constant data and employing Kudriavtsev’s theory which relates the lattice energy of the crystal, <i style="">U</i>, with mean sound velocity, <i style="">u</i>_m, in the crystal. The lattice energies of both MgO and SrO decrease with increase in temperature and the variations are parabolic and similar. The lattice energies of AgCl and TlBr vary with temperature parabolically up to 80 K and thereafter linearly up to 300 K. The results are explained in terms of the structure of the crystals, mutual interaction of the ions and anharmonic effects associated with as a function of temperature. <br/> <br/>Page(s): 660-663 Mon, 29 Aug 2005 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/8860 Title: Analytical model for high temperature performance of non-self aligned SiC MESFET <br/> <br/>Authors: Aggarwal, Sandeep Kr; Gupta, Ritesh; Haldar, Subhasis; Gupta, Mridula; Gupta, R S <br/> <br/>Abstract: An analytical model to evaluate the performance of a non-self-aligned SiC MESFET at elevated temperatures is developed. The formulation, devoid of complex mathematics takes into account all the major effects such as effective mobility, gate-bias dependent parasitic resistances and self-back gating effect. The model evaluates <i style="">I</i>_ds~<i style="">V</i>_ds characteristics, transconductance, channel conductance, intrinsic device capacitances and their dependence on temperature has also been discussed. <br/> <br/>Page(s): 697-704 Mon, 29 Aug 2005 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/8859 Title: Bulk properties of alkali doped C₆₀ solids <br/> <br/>Authors: Ranjan, K; Dharamvir, K; Jindal, V K <br/> <br/>Abstract: The model calculations are presented for potassium, rubidium and cesium doped C₆₀ solids formed by exohedral doping in pure C₆₀ solid. The molecular formula is M_nC₆₀, M is the alkali metal (K, Rb and Cs) and <i style="">n</i> takes integer values 1, 3, 4 and 6.  The C₆₀ molecule is modelled as a uniform spherical shell having surface density of carbon atoms. Part of the electrons released by ionized alkali atoms distributed on the C₆₀ molecule making it an anion, while the rest (say <i style="">x</i>) are assumed to form a delocalised electron gas. This electron gas screens the Coulomb interaction between the various anion and cations. With these assumptions, the total cohesive energy is calculated taking into consideration Van der Waals and screened Coulomb interaction between different ions. We found that the total charge transfer from cation to anion is favoured. Thus ionic character of alkali doped C₆₀ solids is established on the basis of the model. The lattice constant, cohesive energy and Bulk modulus for these systems are in good agreement with other calculation or experimental observations. We make some remarks on phase stability of these solids. <br/> <br/>Page(s): 654-659 Mon, 29 Aug 2005 22:58:59 GMT