Impurity effect on low-temperature polarisation of the charge-density-waves in o-TaS₃

The temperature dependence of the low-temperature dielectric response is studied in o-TaS$_3$ samples doped by Nb, Se, and Ni and for nominally pure ones. It is found, that the low-temperature dielectric constant depends anomalously on doping and is higher for doped crystals, whereas the temperature dependence of the characteristic time of all samples follows the activation law with nearly the same activation energy $\sim 400$ K (T>20 K). The observed behaviour is inconsistent with all available explanations of the low-temperature dielectric anomaly.