Synergistic carrier and phonon transport advance Ag dynamically-doped n-type PbTe thermoelectrics via Mn alloying

Abstract

Optimizing n-type PbTe thermoelectric materials to match their better-performing p-type counterparts is critical for realizing their practical applications. To overcome this gap, dynamic doping, due to its temperature-dependent self-optimizing carrier concentration, has recently arisen as an effective method to improve the performance of n-type PbTe. However, their evitable dynamic compositional evolution must lead to structure evolution at elevated temperatures, which may have a negative effect on suppressing phonon transport, verified by the observed high lattice thermal conductivity (κ_lat) of Ag-doped n-type PbTe. Herein, we describe the significance of Mn alloying in enhancing the performance of Ag-doped n-type PbTe by creating a hierarchical structure to suppress thermal transport and improving the Seebeck coefficient by flattening the L point of the conduction band. Systematic characterization analysis reveals that the constructed hierarchical structure primarily consists of Ag₂Te-decorated grain boundaries, dispersive MnTe nanoprecipitates, and atomic disorders induced by multi-doping in the matrix, which significantly suppressed κ_lat across the entire temperature range. In consequence, a high ZT ∼1.4 of Ag_0.03Pb_0.95Mn_0.05Te at 773 K and an average ZT ∼0.8 of Ag_0.03Pb_0.99Mn_0.01Te in the range of 323–823 K were obtained, which were ascribed to the weakening of the coupling between electron and phonon transport. This work demonstrates an upgraded approach to enhance the thermoelectric performance of dynamically-doped PbTe materials through unique structural design, which can be applied to other thermoelectric material systems with high performance.