High Quality Factor Enabled by Multiscale Phonon Scattering for Enhancing Thermoelectrics in Low-Solubility n-Type...

The fundamental challenge for enhancing the thermoelectric performance of n-type PbTe to match p-type counterparts is to eliminate the Pb vacancy and reduce the lattice thermal conductivity. The Cu atom has shown the ability to fill the cationic vacancy, triggering improved mobility. However, the relatively higher solubility of Cu₂Te limits the interface density in the n-type PbTe matrix, leading to a higher lattice thermal conductivity. In particular, a quantitative relationship between the precipitate scattering and the reduction of lattice thermal conductivity in the n-type PbTe with low solubility of Cu₂Te alloys still remains unclear. In this work, trivalent Sb atoms are introduced, aiming at decreasing the solubility of Cu in PbTe for improving the precipitate volumetric density and ensuring n-type degenerate conduction. Benefiting from the multiscale hierarchical microstructures by Sb and Cu codoping, the lattice thermal conductivity is considerably decreased to 0.38 W m^-1 K^-1. The Debye-Callaway model quantifies the contribution from point defects and nano/microscale precipitates. Moreover, the mobility increases from 228 to 948 cm² V^-1 s^-1 because of the elimination of cationic vacancies. Consequently, a high quality factor is obtained, enabling a superior peak figure of merit ZT of ∼1.32 in n-type Pb_0.975Sb_0.025Te by alloying with only ∼1.2% Cu₂Te. The present finding demonstrates the significant role of low-solubility Cu₂Te in advancing thermoelectrics in n-type PbTe.