Synthesis and Thermoelectric Properties in the 2D Ti1-xNbxS3 Trichalcogenides

A solid solution of Ti1 - xNbxS3 composition (x = 0, 0.05, 0.07, 0.10) was synthesized by solid-liquid-vapor reaction followed by spark plasma sintering. The obtained compounds crystallize in the monoclinic ZrSe3 structure type. For the x = 0.07 sample, a mixture of both A and B variants of the MX3 structure is evidenced by transmission electron microscopy. This result contrasts with those of pristine TiS3, prepared within the same conditions, which crystallizes as a large majority of A variant. Thermoelectric properties were investigated in the temperature range 323 to 523 K. A decrease in the electrical resistivity and absolute value of the Seebeck coefficient is observed when increasing x due to electron doping. The lattice component of the thermal conductivity is effectively reduced by the Nb for Ti substitution through a mass fluctuation effect and/or a disorder effect created by the mixture of both A and B variants. Due to the low carrier concentration and the semiconductor character of the doped compounds, the too low power factor values leads to ZT values that remain smaller by a factor of 50 than those of the TiS2 layered compound.