Dharmendra Kumar Pandey

Ultrasonic wave propagation in rare-earth monochalcogenides

The ultrasonic attenuation in thulium monochalcogenides TmX (X=S, Se and Te) has been studied theoretically with a modified Mason’s approach in the temperature and range 100 K to 300 K along 〈100〉, 〈110〉 〈111〉 crystallographic directions. The thulium monochalcogenides have attracted a lot of interest due to their complex physical and chemical characteristics. TmS, TmSe and TmTe are trivalent metal, mixed valence state, and divalent semiconductor, respectively. Coulomb and Born-Mayer potential is applied to evaluate the second- and third-order elastic constants. These elastic constants are used to compute ultrasonic parameters such as ultrasonic velocities, thermal relaxation time, and acoustic coupling constants that, in turn, are used to evaluate ultrasonic attenuation. A comparison of calculated ultrasonic parameters with available theoretical/experimental physical parameters gives information about classification of these materials.

Elastic and Acoustic Properties of Heavy Rare-Earth Metals

In this paper, ultrasonic properties like ultrasonic attenuation, sound velocities, acoustic coupling constants and thermal relaxation time have been studied in hexagonal structured metals Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er) and Thulium (Tm) along unique axis at room temperature. For the evaluations of ultrasonic properties, secondand thirdorder elastic constants have been computed also. The peculiar behavior of these metals is found at 55° due their least thermal relaxation time and highest Debye average velocity. Dy is more ductile, stable, perfect metal in comparison to other chosen metals due to its lowest value of attenuation. So we predict that Dy is most suitable lanthanide metals for material science and engineering.

ULTRASONIC WAVE PROPAGATION IN SEMI-METALLIC SINGLE CRYSTALS

In this paper, ultrasonic attenuation due phonon–phonon interaction and thermoelastic loss mechanisms has been computed for longitudinal and shear waves along 〈100〉, 〈110〉 and 〈111〉 crystallographic directions in the temperature range 100 K to 300 K using modified Masons approach in gadolinium monopnictides GdX (X: P, As, Sb and Bi). For the evaluation of ultrasonic attenuation with allied factors, the second and third order elastic constants were also evaluated using Coulomb and Born–Mayer type potential considering interaction up to second nearest neighborhood. The thermoelastic loss is not so important in present case due to lesser free electrons than metallic material. GdP is found to be ductile, more perfect, flawless in comparison to GdAs, GdSb and GdBi in this temperature regime and the direction 〈111〉 is more suitable for wave propagation in these B1 structured materials due to low value of attenuation. The mechanical properties of GdP are better than other monochalcogenides because of higher valued elastic constants. The thermal conductivity is the leading factor to study ultrasonic attenuation in these monopnictides. The characteristic features are discussed in correlation with other physical properties like thermal conductivity, specific heat etc.

Synthesis and Nondestructive Characterization of Cr2O3 Nanoparticles-PVA Suspensions

Nanoparticles of chromic oxide (Cr2O3) are widely used in many fields serving as catalysts, wear resistance materials, and advanced colorants. By the reaction system of CrO3 and PVA in aqueous solution, Cr2O3 nanoparticles were prepared via hydrothermal synthesis. We have taken sucrose as reducing agent. The products were loosely agglomerated Cr2O3 particles of 30-80 nm in average particle size calculated from Scherrer’s formula, whose microstructure and the precursor were investigated by SEM. The findings showed that the higher calcination temperatures result in the larger average particle size. Ultrasonic velocity measurements in Cr2O3 nanoparticles suspended in PVA solution were made at different thermal conditions. In the sample Cr2O3+PVA the ultrasonic velocity increases up to 500C and then remains constant. The effort has been made to correlate the ultrasonic velocity/absorption behavior with the magnetic property.