Behaviour of acoustic attenuation in rare-earth chalcogenides

The acoustic attenuation due to phonon–phonon interaction and thermoelastic relaxation mechanisms have been studied for longitudinal and shear waves in B1 structured CeS, CeSe, CeTe, NdS, NdSe and NdTe along 〈1 0 0〉, 〈1 1 0〉 and 〈1 1 1〉 crystallographic directions at room temperature. The second- and third-order elastic constants (SOEC and TOEC) of the chalcogenides are also computed for the evaluation of acoustic parameters. The acoustic attenuation due to phonon–phonon interaction is predominant over thermoelastic loss in these materials. NdS is more ductile, stable and less imperfected material in comparison to other chalcogenides systems (CeS, CeSe, CeTe, NdSe, NdTe, LaS, LaSe, LaTe, PrS, PrSe and PrTe) and rock salt-type LiF single crystal due to its lowest value of attenuation. The value of attenuation along 〈1 1 1〉 crystallographic direction is smaller than the attenuation along 〈1 0 0〉 and 〈1 1 0〉 directions. Hence 〈1 1 1〉 direction is most appropriate to study the physical properties of these materials.