Papers by Author: Prafulla K. Jha

Abstract: Using first principles density functional theoretical calculations within the generalized gradient approximation (GGA), the present paper reports thermal properties such as constant volume lattice specific heat, Gibbs free energy, internal energy, and entropy of Yb-pnictides such as YbN, YbP and YbAs in its rocksalt phase. The variation of lattice specific heat with temperature obeys the classical Dulong-Petits law at high temperature while at low temperature it obeys Debye T³ law. The internal energy, entropy and free energy show a gradual variation with temperature. The specific heat at constant volume at lower temperature increases as going from N to P to As. ^*Corresponding author Email: pkj@bhavuni.edu, prafullaj@yahoo.com Telephone: +91-278-2422650 Fax: +91-278-2426706

Abstract: A detailed theoretical study of structural, electronic and vibrational properties of niobium carbide are carried out in rocksalt phase using the density functional theory implemented in ABINIT code. The calculated structural parameters like lattice constant and bulk modulus agree well with the available data. The Zener anisotropy factor (A), Poison's ratio (v), Young’s modulus (Y) and shear modulus (C’) are also presented. The electronic band structure and density of states are presented and discussed in light of bonding nature in NbC. The band structure indicates its metallic nature. The calculated phonon dispersion curves show that the NbC in rocksalt phase has all positive phonons throughout the Brillouin zone. The thermodynamical properties are also presented and discussed.

Abstract: The present paper presents the carrier-acoustic phonon scattering rate and charge transport in spherical and TMV viruses. We demonstrate theoretically that the absorption rate changes according to the phonon energy while emission of phonon is limited by the both electron and hole energy. The obtained conductivity for spherical and TMV viruses suggest that the TMV virus is more conducting and therefore may be a good candidate for the connector or wire to be used in the nano- and molecular- electronics . The value of resistance obtained for TMV virus is lower than the resistance of DNA.

Abstract: The present paper reports a simple calculation of the size and shape dependent melting temperature of nanoparticles. The melting temperature of any nanoparticle basically depends on the ratio of surface atoms to the total atoms. Significant melting temperature suppression is observed when the particle size approaches the sub-20 nm range. The behavior of melting temperature is similar for the larger nanoparticles of all considered shapes but differs significantly for small nanoparticles. Different melting temperature is predicted for the nanoparticles of the same size in different shapes.

Abstract: Soft magnetic alloys consisting of nanoscale fcc Fe grains have been developed by primary crystallization of melt-spun amorphous alloys as typically exemplified in Fe-B[1], Fe-M-B (M = Zr, Hf, Nb) (Nanoperm) [2] and Fe-Si-B-Nb-Cu (FINEMET)systems[3]. Lot of scientific effort has been put in last years to control the crystallization process of metallic glasses. This is due to the fact that several attractive properties of the resulting material are strongly related to the final attained microstructure. In the present paper, primary nanocrystallization kinetics of a Fe–based multicomponent amorphous system namely Fe67Co18B14Si1 (2605CO) has been analysed by nonisothermal DSC measurements. Crystallization is a combined process of nucleation and growth. The amorphous alloy undergoes two-step crystallization with primary crystallization of α-Fe giving the first step. The Avrami exponent for the two steps has been derived. A detailed analysis of the data provides an insight in to the dimensionality and mechanism of growth.