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.

Co-intercalation of nickel and excess titanium into the van der Waals gap of TiSe2 via solid state synthesis followed by spark plasma sintering results in a systematic shift in the ratio of hole and electron carrier concentration, which is close to unity for pristine TiSe2. This directly affects the electrical transport properties, and as the structural disorder induced by intercalation suppresses the lattice thermal conductivity, co-intercalation is an effective route to enhance the thermoelectric properties of transition metal diselenides. Figure optionsDownload as PowerPoint slideHighlights
► Single phase bulk Ni and Ti co-intercalated TiSe2 samples prepared by spark plasma sintering.
► Density and X-ray diffraction suggest that the Ni and excess Ti are ordered in the Van der Waals gap.
► Co-intercalation of Ni and Ti can be used to control electron–hole ratio and structural disorder.