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DFT study of optoelectronic spectra of barium cadmium chalcogenides (Ba2CdX3, X = S, Se and Te)

Kumar Sachin, Kumar Naven, Yadav Kamna, Annveer, Singh R. P.

Materials Science Poland

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2019

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Vol. 37, No. 3

417--425

EN

DFT analyses of electronic and optical spectra of barium cadmium chalcogenides (Ba2CdX3, X = S, Se, Te) have been carried out. The study of electronic spectra has been made in terms of band structure and density of states using full potential linear augmented plane wave plus local orbital method. Band structure calculations have been carried out under the approximations PBE-GGA, PBE-Sol, LDA and TB-mBJ. Band structures of these materials show that Ba2CdS3, Ba2CdSe3 and Ba2CdTe3 crystals possess a band gap less than 1 eV, underestimated relative to the experimental/theoretical literature values. Optical spectra of these chalcogenides have been analyzed in terms of real and imaginary parts of dielectric function, reflectivity, refractive index, extinction coefficient, absorption coefficient, optical conductivity and electron energy loss. Optical results show large anisotropy along different directions. These results provide a physical basis of barium cadmium chalcogenides for potential application in optoelectronic devices.

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Acoustical investigations of uranium chalcogenides

Singh R. K., Pandey K. K., Singh M. P., Singh R. P.

Materials Science Poland

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2009

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Vol. 27, No. 4/1

1041--1053

EN

Ultrasonic attenuation due to phonon-phonon interaction and thermoelastic loss was evaluated in uranium chalcogenides viz. UX, X= S, Se, Te in fcc phase in the temperature range 50-600 K for longitudinal and shear waves along the <100>, <110> and <111> directions of propagation. Electrostatic and Born-Mayer repulsive potentials were used to obtain second and third order elastic constants, taking the nearest neighbour distance and hardness parameter as the input data. Second and third order elastic constants (obtained at various temperatures) were used to obtain the Gruneisen parameters and non-linearity or anisotropy parameters, which in turn were used to evaluate the ultrasonic attenuation coefficient over the frequency square due to phonon-phonon interaction, (?/f 2)p-p in the Akhiezer regime. It has been found that at lower temperatures ?/f 2 increases rapidly with temperature, and at higher temperatures the rate of increase becomes small. Contribution to the total attenuation due to thermoelastic loss is negligible in comparison with that of phonon-phonon interaction, i.e. a major part of the energy from the sound wave is removed, due to interaction of acoustic phonons with thermal phonons (lattice vibrations).

3

Heat transfer due to permeable stretching. Wall in presence of transverse magnetic field

Dandapat B. S., Singh S. N., Singh R. P.

Archives of Mechanics

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2004

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Vol. 56, nr 1

87-101

EN

Exact similarity solution for the viscous flow due to stretching surface in the presence of magnetic field is derived. Further exact solutions for the temperature distributions in terms of Kummer's functions are obtained. Two cases of heat transfer are considered: the sheet (i) with prescribed surface temperature and (ii) - the prescribed wall heat flux. Both the cases are further extended to study the heat transfer due to suction and injection. A simple relation for the two cases of heat transfer is obtained.