Tuning of thermoelectric performance by modulating vibrational properties in Ni-doped Sb₂Te₃

Sb₂Te₃, a binary chalcogenide-based 3D topological insulator, attracts significant attention for its exceptional thermoelectric performance. We report the vibrational properties of magnetically doped Sb₂Te₃thermoelectric material. Ni doping induces defect/disorder in the system and plays a positive role in engineering the thermoelectric properties through tuning the vibrational phonon modes. Synchrotron powder x-ray diffraction study confirms good crystalline quality and single-phase nature of the synthesized samples. The change in structural parameters, includingB_isoand strain, further corroborate with structural disorder. Detailed modification of phonon modes with doping and temperature variation is analysed from temperature-dependent Raman spectroscopic measurement. Compressive lattice strain is observed from the blue shift of Raman peaks owing to Ni incorporation in Sb site. An attempt is made to extract the lattice thermal conductivity from total thermal conductivity estimated through optothermal Raman studies. Hall concentration data support the change in temperature-dependent resistivity and thermopower. Remarkable increase in thermopower is observed after Ni doping. Simulation of the Pisarenko model, indicating the convergence of the valence band, explains the observed enhancement of thermopower in Sb_2-xNi_xTe₃. The energy gap between the light and heavy valence band at Γ point is found to be 30 meV (for Sb₂Te₃), which is reduced to 3 meV (in Sb_1.98Ni_0.02Te₃). A significant increase in thermoelectric power factor is obtained from 715 μWm^-1K^-2for pristine Sb₂Te₃to 2415 μWm^-1K^-2for Ni-doped Sb₂Te₃sample. Finally, the thermoelectric figure of merit,ZTis found to increase by four times in Sb_1.98Ni_0.02Te₃than that of its pristine counterpart.