Thermoelectric properties of Fe and Al co-added Ge

The polycrystalline bulk samples of Fe and Al co-added Ge were synthesized by melt-spinning followed by spark plasma sintering and the thermoelectric properties were examined. Here, Al acts as a p-type dopant, while Fe is expected to form FeGe2 as precipitates. Since the lattice mismatch between Ge and FeGe2 is small (< 4%), they would coherently connect with each other, reducing the thermal conductivity without affecting the electrical transport. In this study, a reduction in thermal conductivity was achieved by dispersing the FeGe2 precipitates in the Aldoped Ge matrix, while they had little influences on both the carrier mobility and the Seebeck coefficient. As the results, the maximum ZT value of 0.13 was obtained at 773 K, which is three times higher than that of single-crystal Ge reported by the authors' group [Y. Ohishi et al., Jpn. J. Appl. Phys. 55, 051301 (2016)]. (C) 2017 The Japan Society of Applied Physics