A study of Yb0.2Co4Sb12–AgSbTe2 nanocomposites: simultaneous enhancement of all three thermoelectric properties

Abstract

The single-filled skutterudite Yb_0.2Co₄Sb₁₂ has been long known as a promising bulk thermoelectric material. In this work, we adopted a melting–milling–hot pressing procedure to prepare nanocomposites that consist of a micrometer-grained Yb_0.2Co₄Sb₁₂ matrix and well-dispersed AgSbTe₂ nanoinclusions on the matrix grain boundaries. Different weight percentages of AgSbTe₂ inclusions were added to optimize the thermoelectric performance. We found that the addition of AgSbTe₂ nanoinclusions systematically and simultaneously optimized the otherwise adversely inter-dependent electrical conductivity, Seebeck coefficient and thermal conductivity. In particular, the significantly enhanced carrier mobility led to a ∼3-fold reduction of the electrical resistivity. Meanwhile the absolute value of Seebeck coefficient was enhanced via the energy filtering effect at the matrix–nanoinclusion interfaces. Moreover there is a topological crossover of the AgSbTe₂ inclusions from isolated nanoparticles to a nano-plating or nano-coating between 6 wt% and 8 wt% of nanoinclusions. Above the crossover, further addition of nanoinclusions degraded the Seebeck coefficient and the electrical conductivity. Meanwhile, the addition of nanoinclusions generally reduced the lattice thermal conductivity. As a result, the power factor of the 6 wt% sample was ∼7 times larger than that of the nanoinclusion-free sample, yielding a room temperature figure of merit ZT ∼ 0.51.