To date, reducing grain size to the nanoscale has been the only widely known strategy for enhancing the weighted mobility ratio (A), which is a key parameter that governs bipolar conduction in narrow-band-gap thermoelectrics at elevated temperatures. Here, we present an alternative approach based on magnetic nanoparticle-enabled carrier filtering that effectively increases A and suppresses bipolar transport in p-type Bi0.4Sb1.6Te3 (BST). Using a solvent-free metal-decoration method, ferromagnetic Fe or Co nanoparticles are homogeneously incorporated into the BST matrix. These nanoparticles generate local magnetic fields and introduce interfacial band offsets, which selectively hinder the transport of low-energy carriers. Two-band model analysis reveals that Fe incorporation enhances A by increasing the asymmetry between hole and electron mobility, while also reducing carrier concentration via Lorentz-force-mediated scattering of minority carriers. As a result, the Fe-decorated sample achieves a peak zT ∼1.24 at 363 K and maintains zT > 1 up to 420 K, with a value of zT ∼0.87 at 483 K, which represents a ~ 50% improvement compared to pristine BST. This study establishes magnetic nanoparticle incorporation as an effective and generalizable route to enhance the A and engineer bipolar conduction in narrow-gap thermoelectric materials.
Ye et al. (Mon,) studied this question.