Enhanced power factor and suppressed lattice thermal conductivity of CoSb3 skutterudite via Ni substitution and nanostructuring for high thermoelectric performance

Abstract

Nanostructured Ni-substituted Co_1−xNi_xSb₃ (0 ≤ x ≤ 0.08) samples were synthesized using a hydrothermal method. X-ray diffraction analysis confirmed the phase purity of the samples, and a secondary phase was observed in samples with higher Ni substitution ratios (x ≥ 0.06). SEM and TEM images reveal the spherical morphology of the samples with monodispersed particles. Different modes of optic phonon vibrations were observed in Raman spectra, and the intensity of the peaks increased with Ni content and slightly decreased in samples with x values ≥0.06. The electrical resistivity of the samples decreased with Ni content up to an x value of 0.06 and slightly increased in Co_0.92Ni_0.08Sb₃ due to secondary phase formation. The positive Seebeck coefficient values of pure CoSb₃ confirm that holes were the majority carriers, whereas the negative Seebeck coefficients of Co_1−xNi_xSb₃ samples reveal that Ni substitution enhanced electron concentration in the sample. Co_0.96Ni_0.04Sb₃ exhibited a higher power factor compared with other samples due to its low resistivity. Ni substitution in CoSb₃ effectively reduced lattice thermal conductivity (κ_L) as Co_0.96Ni_0.04Sb₃ showed a lower κ_L of 2.0 W m⁻¹ K⁻¹ than that of the pure sample due to nanostructuring and the rattling effect of Ni. As a result, a figure of merit of 1.72 was achieved at 553 K for the Co_0.96Ni_0.04Sb₃ sample.