High Thermoelectric Performance in Rhombohedral GeSe-LiBiTe₂

Area of Science:

• Materials Science
• Solid State Physics
• Thermoelectrics

Background:

• Germanium selenide (GeSe) shows potential for thermoelectric applications but is limited by dopability challenges.
• Optimizing carrier concentration is crucial for improving the thermoelectric figure of merit (ZT).

Purpose of the Study:

• To develop a crystal structure evolution strategy for highly doped GeSe with enhanced thermoelectric properties.
• To investigate the impact of LiBiTe2 alloying on GeSe's crystal structure, electronic band structure, and thermoelectric performance.

Main Methods:

• Alloying GeSe with LiBiTe2 to induce crystal structure evolution (rhombohedral to cubic phases).
• Characterization of electronic band structure and carrier concentration.
• Measurement of lattice thermal conductivity and thermoelectric figure of merit (ZT) across a temperature range.

Main Results:

• Stabilization of rhombohedral (R3m) and cubic (Fm3̅m) phases in GeSe-LiBiTe2 alloys.
• Observation of converged multiple-valley valence bands (L and Σ bands) leading to high carrier concentration (~10^20 cm^-3) and enhanced power factor.
• Achieved ultra-low lattice thermal conductivity (0.6-0.5 W m^-1 K^-1) due to phonon scattering mechanisms.
• Maximum ZT of 1.1-1.3 at 723 K and average ZT > 0.8 (400-723 K) in 0.9GeSe-0.1LiBiTe2.

Conclusions:

• Crystal structure engineering via alloying is an effective strategy to overcome dopability limitations in GeSe.
• The GeSe-LiBiTe2 system demonstrates significant potential for high-performance thermoelectric materials.
• This work provides a pathway for tailoring thermoelectric performance in GeSe-based compounds.