Low-temperature thermal conductivity of a single-grain Y-Mg-Zn icosahedral quasicrystal

We report measurements of the thermal conductivity kappa(T) of a single-grain icosahedral Y8.6Me34.6Zn56.8 in the temperature range between 0.1 and 300 K. The quasilattice thermal conductivity kappa(ph) increases monotonically with T by three orders of magnitude between 0.1 and 23 K. Above 23 K, kappa(ph)(T) decreases substantially with increasing temperature, typical for high-quality single grain quasicrystals. The decrease ends in a minimum at approximately 140 K. The interpretation of our data is based on a Debye-type relaxation time approximation. At very low temperatures, the corresponding fit reveals that the phonon mean free path is of the order of the smallest sample dimension, while at high temperatures, a power-law decrease of the phonon scattering time with increasing temperature evidences the effect of structural scattering on the mean free path of itinerant quasilattice excitations. The behavior of kappa(ph)(T) at intermediate temperatures may best be fit by assuming the existence of stacking-fault-like phonon scatterers. No clear evidence for a scattering of phonons by tunneling states has been observed. If compared to previously reported measurements of the thermal conductivity of quasicrystals, these data indicate the very high structural perfection of this quasiperiodic material.