Work

Lattice instability and elastic dispersion due to the rattling motion in the type-I clathrate Ba 8 Ga 16 Sn 30

Year: 2012

Type: article

Abstract: To investigate the off-center rattling motion and its charge-carrier dependence in type-I clathrate compounds, we carried out ultrasonic measurements on type-I Ba${}_{8}$Ga${}_{16}$Sn${}_{30}$ and a reference compound, K${}_{8}$Ga${}_{8}$Sn${}_{38}$. We found elastic softening of ${C}_{44}$ originating from a lattice instability due to the off-center rattling motion of Ba atom in Ba${}_{8}$Ga${}_{16}$Sn${}_{30}$. Elastic softening below 1 K suggests that the lattice instability remains at very low temperatures. We also found ultrasonic dispersion which has no mode selectivity. No-mode-selective ultrasonic dispersion in Ba${}_{8}$Ga${}_{16}$Sn${}_{30}$ would be caused by a strong electron-phonon coupling. No charge-carrier dependence is observed between $n$-type and $p$-type Ba${}_{8}$Ga${}_{16}$Sn${}_{30}$. The significant softening on the bulk modulus in Ba${}_{8}$Ga${}_{16}$Sn${}_{30}$ contrasts to the continuous hardening in K${}_{8}$Ga${}_{8}$Sn${}_{38}$, indicating the central role of the rattling motion in the softening.

Source: Physical Review B

DOI: 10.1103/physrevb.85.085101