Influence of pulsed-electric-current sintering conditions on the non-stoichiometry and thermoelectric properties of Ti1 + xS2

Nearly stoichiometric Ti1.005S2 was prepared by a solid-state synthesis of the constituent elements and consolidated under a variety of processing conditions applied using pulsed-electric-current sintering. The non-stoichiometry in the Ti1+xS2 induced during the sintering was quantitatively determined with a Rietveld structural refinement and a thermogravimetric analysis combined with inductively coupled plasma atomic emission spectroscopy. Significant cation off-stoichiometry and sulphur losses were already observed at a sintering temperature of 700°C, resulting in heavily self-intercalated Ti1.076S2, which significantly altered the thermoelectric properties in comparison with the nearly stoichiometric compound. By applying a high sintering pressure of 500MPa the Ti1.005S2 could be consolidated at 500°C with no detectable sulphur loses and with a high bulk density of 97.6%. The sulphur volatilization in the TiS2 was also effectively suppressed up to 800°C by using a gas-tight sintering mould, which resulted in the composition Ti1.017S2, prepared at 800°C and 200MPa, with an optimal thermoelectric figure of merit ZT equal to 0.32 at 375°C.