Enhanced thermoelectric performance in Ga Co4Sb12.3-Te skutterudites via suppressing bipolar effects for commercial application

The n-type filled and doped skutterudites GaxCo4Sb12.3 and Ga0.2Co4Sb11.3Te composites with the well-distributed GaSb nanoinclusions are synthesized through the manipulating of metastable Ga fillers and enrichment of Sb by an in-situ method with a proper annealing procedure. Ga atoms can fill the icosahedron cages of skutterudite at high temperature, but at low temperature, they are driven out from the lattice voids and form the second phase of GaSb at grain boundaries. The presence of GaSb second phases reduces the thermal conductivity effectively. Te doping leads to a significant increase in carrier concentration of Ga0.2Co4Sb11.3Te, thus largely suppresses the bipolar effect of GaxCo4Sb12.3, resulting in a great enhancement in power factor. Moreover, Te doping induces mass and strain fluctuation, which decreases the lattice thermal conductivity further. Consequently, the maximum ZT is increased from 0.56 for Ga0.2Co4Sb12.3 at 573 K to 1.48 for Ga0.2Co4Sb11.3Te at 873 K, which is advantageous to improve the thermoelectric conversion efficiency for commercial application.