Defect and Dopant Mediated Thermoelectric Power Factor Tuning in β-Zn₄Sb₃

The presence of defects in thermoelectric materials plays a significant role in the modification their properties by influencing the behavior of electrons and phonons. Dopants with a unique f-orbital can directly cause distortions in electronic density of states (eDOS) and phonon transport mechanism by intentionally inducing defects in their lattice. The theoretical and experimental outcomes of engineered vacancy defects are investigated by intentional doping of f-block rare earth elements in β-Zn₄Sb₃. Thermoelectric behavior breaks down the inverse relation and results in a parallel increase in Seebeck coefficient and electrical conductivity for β-(Zn_0.997Ce_0.003)₄Sb₃ and β-(Zn_0.997Er_0.003)₄Sb₃. This synergistic response triples the power factor of a thermoelectric β-Zn₄Sb₃ system realized by the impurity induced resonant distortion in eDOS. From first principle GGA + U calculations, the above-mentioned unconventional properties are attributed to the effect of doping induced vacancy formation and the formation of resonant impurity levels. Hence, it is postulated that defect engineering can be a broad strategy to improve the power factor of the system and can be extended to other thermoelectric materials.