Glass-like thermal transport in symmetry-broken clathrates
We present the quantitative interpretation for the glass-like behavior of thermal conductivities κ(T) for type-I clathrate compounds involving off-centered guest ions. It is shown that the dipole-dipole interaction generated in cage/guest-ion systems is crucial to reproduce the characteristics of thermal conductivities for these symmetry-broken clathrates. The above scenario also explains well the difference of κ(T) between the p-type and the n-type β-BGS found recently by K. Suekuni et al. (Phys. Rev. B, 77 (2008) 235119.)
Emergence of glass-like THz frequency libration modes in type-I clathrates: Theory
Abstract A theory is given of a role of rattling guest ions to the emergence of THz frequency libration modes in type-I clathrates involving off-centered guest ions. We clarify the physical origin of distinct differences on THz frequency dynamics between on-center and off-center systems. It is demonstrated that the spontaneous symmetry breaking of rattling off-centered guest ions is a key for the emergence of low-lying band-modes hybridized with acoustic modes in the THz-frequency range.
Secoiridoids from Olea europaea
Abstract Three new secoiridoids have been isolated from the leaves of Olea europaea along with the previously reported. The compounds were identified by spectral means.