Theoretical study of lattice dynamics in LaB6 and YbB6

Abstract

Abstract Elastic constants and phonon dispersion curves of LaB6 and YbB6 are calculated theoretically. In LaB6, a small value of the elastic constant C12 is explained by the volume dependent force acting on La atoms. Furthermore, introducing the long range force between La atoms, we get the phonon dispersion curves in good agreement with the measured ones. In YbB6, too, the calculated phonon dispersion curves are consistent with the measured elastic constants and temperature dependence of specific heat. The origin of the volume dependent and long range forces is considered.