Large reduction of thermal conductivity leading to enhanced thermoelectric performance in p-type Mg ₃ Bi ₂ -YbMg ₂ Bi ₂ solid solutions

Intensifying the phonon scattering via point defect engineering has been demonstrated to be particularly effective in minimizing the lattice thermal conductivity for enhancing thermoelectric performance. In this work, significant phonon scattering has been realized by alloying YbMg ₂ Bi ₂ with Mg ₃ Bi ₂ . The substantial mass difference between the host atom Yb and the alloying atom Mg leads to an intense phonon scattering effect that significantly reduces the lattice thermal conductivity. The room-temperature lattice thermal conductivity decreases from ∼2.7 W m ^-1 K ^-1 for YbMg ₂ Bi _1.96 to ∼0.8 W m ^-1 K ^-1 for Yb _0.7 Mg _0.3 Mg ₂ Bi _1.96 , a reduction of ∼70%. Benefiting from the greatly reduced thermal conductivity, the average ZT has been effectively improved from ∼0.46 for YbMg ₂ Bi _1.96 to ∼0.61 for Yb _0.8 Mg _0.2 Mg ₂ Bi _1.96 , an enhancement of ∼33%. In addition, the predicted maximum heat-to-electricity conversion efficiency can be increased from ∼7% for YbMg ₂ Bi _1.96 to ∼10% for Yb _0.8 Mg _0.2 Mg ₂ Bi _1.96 .