Achieving synergistic performance through highly compacted microcrystalline rods induced in Mo doped GeTe based compounds

Among the lead-free thermoelectric material, germanium telluride (GeTe) has been extensively investigated due to its high thermoelectric performance (ZT) in mid-temperature; however, high p-type carrier density (∼10²¹ cm⁻³) hinder its suitability for higher ZT. To enhance the thermoelectric performance of the environmentally favorable GeTe, we explored the Mo doping significantly optimizes the carrier concentration along with uniquely unveiled microcrystalline rods accompanying compact grain boundaries, high-density planar defects, and point defects effectuating all-frequency phonon scattering yields to lower down the thermal conductivity. Furthermore, Sb/Bi co-doping with Mo at the Ge sites predominantly reduces the carrier concentration and thermal conductivity to attain a higher ZT. The co-doping of Bi manifested a more prominent role in achieving the highest ZT of ∼2.3 at 673 K for the sample composition with Ge_0.89Mo_0·01Bi_0.1Te. This study demonstrates an exciting hidden aspect of microstructural modification by forming highly dense microcrystalline rods through Mo doping to achieve high performance in the GeTe system.