Low-temperature thermal conductivity of CaB₆and EuB₆

The thermal conductivities of stoichiometric CaB 6 , vacancy-doped Ca 1− δ B 6 , and EuB 6 have been measured between 6 and 300 K. All our data may be rather well described across the entire temperature regime covered on the basis of a Debye-type relaxation-time approximation and by assuming the concurring influence of various scattering channels on the mean free path of the phonons. An unusual and strong resonance in the scattering rate of the phonons of all investigated materials is attributed to a strong interaction between acoustic itinerant and localized modes, the latter arising from oscillations of the metal cations around their equilibrium position.