ULTRASONIC WAVE PROPAGATION IN SEMI-METALLIC SINGLE CRYSTALS

Abstract

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 Mason's 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.