High Thermoelectric Performance Achieved in Nb_0.8Ti_0.2FeSb via PbI₂-Driven Multiscale Defect Engineering

Area of Science:

• Materials Science
• Solid State Physics
• Thermoelectrics

Background:

• NbFeSb-based half-Heusler alloys possess good electrical and mechanical properties but are limited by high lattice thermal conductivity.
• Reducing thermal conductivity in these alloys is challenging due to high-temperature processing requirements for complex microstructures.

Purpose of the Study:

• To develop a method for creating hierarchical microstructures in NbFeSb alloys to reduce thermal conductivity.
• To investigate the impact of these microstructures on thermoelectric and mechanical properties.

Main Methods:

• Incorporation of PbI₂ during ball-milling of Nb_0.8Ti_0.2FeSb.
• Sublimation of PbI₂ during high-temperature sintering to form hierarchical structures.
• Characterization of microstructures, thermal conductivity, electrical conductivity, power factor, and mechanical properties.

Main Results:

• Hierarchical structures including PbI₂ nanophases, core-shell pore@Pb structures, multiscale porosity, and Fe vacancies were formed.
• Lattice thermal conductivity was reduced by 32% to 3.34 W m^-1 K^-1 at 973 K due to full-spectrum phonon scattering and lattice softening.
• Power factor reached 52.7 µW cm^-1 K^-2 (zT ~ 1) with improved electrical conductivity.
• Compressive strength increased by 38% to 1132 MPa, and microhardness reached 950 HV.

Conclusions:

• Sublimable compounds effectively create hierarchical architectures in high-temperature thermoelectrics.
• This approach simultaneously enhances thermoelectric efficiency and mechanical robustness.
• The developed method offers a pathway for advanced thermoelectric materials.