Experimental evidence of the role of quasilocalized phonons in the thermal conductivity of simple alcohols in orientationally ordered crystalline phases

The thermal conductivity κ(T) of crystalline alcohols (methyl, ethyl and 1-propyl) within their thermodynamic equilibrium phases for T⩾2K and under the equilibrium vapor pressures has been measured and analyzed. While such compounds usually exhibit a rich polymorphism including amorphous and partially ordered crystals, the phases here explored correspond to crystals showing complete orientational order. The results show that the temperature dependence of κ(T) above its maximum deviates from the expected 1∕T-law decrease with increasing temperature, arising from anharmonic interactions involving acoustic excitations. Such a deviation is here attributed to the presence of a component κII(T) corresponding to the shortest-lifetime phonons (Cahill-Pohl model), in addition to the component κI(T) related to propagating phonons and thus: κ(T)=κI(T)+κII(T). Above T=40K, κI(T) does follow the 1∕T law and κII(T) is basically temperature independent. The component κI(T) is well described by the Debye-Peierls model ta...