Electronic, Thermal, and Thermoelectric Properties of Ni-Doped FeTe₂ Polycrystalline Alloys

Recently, transition metal dichalcogenides are being actively researched as thermoelectric materials. Among those, FeTe₂ alloys exhibits both n-type and p-type conduction in different temperature range and thus their practicality as a thermoelectric material is somewhat limited. In this study, the effect of Ni addition on the electrical and thermal transport properties of FeTe₂ was investigated by synthesizing a series of Ni-doped FeTe₂ polycrystalline alloys. Fe_{1 − x}Ni_xTe₂ (x = 0, 0.025, 0.05, 0.075, and 0.1). The electrical conductivity gradually increased from 323 S/cm (x = 0) to 688 S/cm (x = 0.1) at 300 K and from 905 S/cm (x = 0) to 1510 S/cm (x = 0.1) at 600 K. The change is mainly attributed to an increase in carrier concentration by the Ni doping. In addition, the Ni doping converted FeTe₂ to an n-type conductor above 400 K. The power factor was increased to 0.11–0.15 mW/mK² for the Ni-doped sample, compared to 0.05 mW/mK₂ for FeTe₂ at 600 K. The thermal conductivity decreased from 3.36 W/mK (x = 0) to 2.02 W/mK (x = 0.1) at 300 K owing to a significant decrease in lattice thermal conductivity resulting from point defect phonon scattering induced by Ni doping. Consequently, a maximum zT value of 0.029 at 600 K was observed for x = 0.075 in Fe_{1 − x}Ni_xTe₂.which is more than 4-fold increase compared to zT of 0.0065 of FeTe₂. Graphical Abstract: [Figure not available: see fulltext.]