Thermoelectric transport properties of polycrystalline titanium diselenide co-intercalated with nickel and titanium using spark plasma sintering

Polycrystalline samples of nickel intercalated (0–5%) TiSe2 were attempted via solid-state reaction in evacuated quartz tubes followed by densification using a spark plasma sintering process. X-ray diffraction data indicated that mixed NiSe2 and TiSe2 phases were present after initial synthesis by solid-state reaction, but a pure TiSe2 phase was present after the spark plasma sintering. While EPMA data reveals the stoichiometry to be near 1:1.8 (Ti:Se) for all samples, comparisons of the measured bulk densities to the theoretical densities suggest that the off stoichiometry is a result of the co-intercalation of both Ni and Ti rather than Se vacancies. Due to the presence of excess Ti (0.085–0.130 per formula) in the van der Waals gap of all the samples, the sensitive electron–hole balance is offset by the additional Ti-3d electrons, leading to an increase in the thermopower (n-type) over pristine, stoichiometric TiSe2. The effects of the co-intercalation of both Ni and Ti in TiSe2 on the structural, thermal, and electrical properties are discussed herein.