LOW-TEMPERATURE PHONON THERMAL-CONDUCTIVITY OF THE QUASI-ONE-DIMENSIONAL COMPOUNDS (NBSE4)3I, (TASE4)2I AND K0.3MOO3

We report on measurements of the thermal conductivity of quasi-one-dim ensional compounds K0.3MoO3, (NbSe4)3I, and (TaSe4)2I between 0.07 K a nd 4 K. Despite the presence of a charge-density wave, the observed be haviour is similar to that expected in good insulating crystals, where the thermal conductivity well below 1 K is mainly governed by boundar y scattering with some degree of specular reflection. However a pronou nced anomaly is detected in (TaSe4)2I as a sharp maximum around 1 K, f ollowed by a broad minimum around 3 K. We ascribe this anomaly to stro ng scattering by low-lying transverse acoustic phonons, with a very we ak dispersion over a large part of the Brillouin zone, lying at an unu sually low frequency.