Dramatic Enhancement of Thermoelectric Performance in PbTe by Unconventional Grain Shrinking in the Sintering Process

Nanostructure engineering is a key strategy for tailoring properties in the fields of batteries, solar cells, thermoelectrics, and so on. Limited by grain coarsening, however, the nanostructure effect gradually degrades during the materials' manufacturing and in-service period. Herein, a strategy of cleavage-fracture for grain shrinking is developed in a Pb_0.98 Sb_0.02 Te sample during sintering, and the grain size remains stable after repeated tests. Moreover, the initial grain boundary is filled by fractured slender grains and enriched by dislocations, evolving into a hierarchical grain-boundary structure. The lattice thermal conductivity (k_lat ) is greatly reduced to approach the amorphous limit. As a result, a record-high ZT value of ≈1.9 is obtained at 815 K in the n-type Pb_0.98 Sb_0.02 Te sample and a decent efficiency of 6.7% in thermoelectric device. This strategy for grain shrinking will shed light on the application of nanostructure engineering under high temperature and extreme conditions in other material systems.