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## Thermoelectric power and its correlation with conductivity in NbS3 whiskers

We report studies of the Seebeck coefficient S of the quasi-one-dimensional compound NbS3, together with the temperature dependence of its specific conductivity σs and heat capacity cp. The monoclinic phase (NbS3-II) is studied over the temperature range T = 80–400 K, which covers two charge density wave (CDW) transitions at TP1 = 360 K (CDW-1) and TP2 = 150 K (CDW-2). The S(T ) curves show features in the vicinities of both CDW transitions and appear to be correlated with the value of σs(300 K): The increase of S below TP1 in the high-Ohmic samples reveals a complete dielectrization of the electronic spectrum, while in the low-Ohmic samples S decreases below TP1 and even becomes negative below TP2. The magnitude of S in low-Ohmic samples at T < TP2 is well below kB/e ≈ 86 μV/K, kB being the Boltzmann constant and e the elementary charge, which is surprisingly low for a usual CDW semiconducting state. Our results suggest that at TP1 the main electronic band with p-type carriers becomes gapped, while some n-type carriers can remain in a separate band with low density of states. These carriers, whose concentration is defined by the compositional doping, are gapped at TP2. We also report S for the triclinic dielectric phase of NbS3 (NbS3-I). Its low absolute value, ∼kB/e, and the anomalous tem- perature dependence demonstrate that NbS3 -I is neither a semiconductor nor a CDW conductor in the usual sense.