Magnetically Enhanced Thermoelectric Performance of Ti_0.75NiSb+x mol % Fe (x = 0–5) Nanocomposites

Ti0.75NiSb is a half-Heusler compound with low lattice thermal conductivity due to a large number of cation vacancies. However, the higher carrier concentration limits the improvement of its thermoelectric performance. In this paper, magnetic Fe nanoparticles with a size of 30 nm are composited into Ti0.75NiSb in the form of the second phase. The charge transfer between Fe nanoparticles and Ti0.75NiSb leads to a decrease in carrier concentration. The strong interaction between the magnetic moment and carriers enhances the electron scattering, so that the scattering factor increases and the mobility decreases. The combined effect results in an increase of about 10% in the Seebeck coefficient and a decrease by about 14% in the electronic thermal conductivity at 873 K for the composite Ti0.75NiSb+2 mol % Fe. Meanwhile, the magnetic Fe nanoparticles provide additional scattering centers, leading to a decrease in lattice thermal conductivity. As a result, a zT value of 0.4 at 873 K is achieved for the composite Ti0.75NiSb+2 mol % Fe, which is 21% higher than that of Ti0.75NiSb. This work demonstrates that the compositing magnetic nanoparticles Fe can enhance the thermoelectric performance of Ti0.75NiSb.