Rare-Earth Atomic Motion in RBe₁₃ (R: La, Pr, Sm)

Abstract

Inelastic X-ray scattering and nuclear resonant inelastic scattering has been applied to a series of RBe 13 to understand the motion of their rare-earth atoms. The combination of 149 Sm nuclear resonant inelastic scattering and inelastic X-ray scattering has clarified that nearly flat dispersions observed around 15 meV correspond to the Sm atomic motion in the Be cage of SmBe 13. Evident rare-earth dependence of the phonon energy at the X positions, which correspond to nearly flat dispersions, have also been found in LaBe 13 , PrBe 13 and SmBe 13. The rare-earth dependence implies that the phonon energy is correlated with the presence of an anharmonic potential at the 8a site as well as atomic mass of the rare-earth.