Enhanced thermoelectric performance in p-type Ca0.5Ce0.5Fe4−xNixSb12 skutterudites by adjusting the carrier concentration

Polycrystalline p-type Ca/Ce co-filled skutterudites Ca0.5Ce0.5Fe4−xNixSb12 (0 ≤ 0 ≤ 0.7) compounds have been successfully prepared by traditional melting-annealing-spark plasma sintering (SPS) method. The effective adjustment in carrier concentration dominates electronic transport behavior in a manner of significant decrease of electrical conductivity as well as the enhancement in Seebeck coefficient with increasing Ni-substitution, resulting in a slight degradation of power factor. Meanwhile, the thermal conductivity, dominated by electronic contribution, decreases monotonically with increasing Ni-substitution, and the negligible mass fluctuation between Ni and Fe gives rise to a slight change in phonon thermal conductivity. In particular, the lattice thermal conductivity of these co-filled skutterudites shows rather low value compared with other double filled analogs due to the large difference in localized frequencies between Ca and Ce elements. Due to the opposite tendency between electronic properties and thermal conductivities, ZT governed by carrier concentration increases firstly and then decreases. The maximum ZT value of 0.85 at 700 K is obtained in the sample Ca0.5Ce0.5Fe3.5Ni0.5Sb12 with a carrier concentration of ∼2.6 × 1020 cm−3, and this peak value is comparable to some excellent p-type skutterudites reported so far. This study demonstrates that the effective control in carrier concentration can be easily realized through proper Fe-site substitutions without deterioration in carrier mobility and change in electronic structure, thus bringing about an optimization of thermoelectric figure of merit.

► Ca and Ce co-filling was realized in iron-rich based p-type skutterudites for the first time.
► Ca and Ce co-filled skutterudites possess extremely low lattice thermal conductivity compared with other filled systems.
► The introduction of Ni regulates the carrier concentration and thermoelectric transport properties effectively.