Nanostructures in high-performance (GeTe)(x)(AgSbTe(2))(100-x) thermoelectric materials

Area of Science:

• Materials Science
• Solid State Physics
• Nanotechnology

Background:

• Thermoelectric materials efficiently convert heat into electricity.
• Optimizing thermoelectric performance requires balancing electrical conductivity and thermal conductivity.
• GeTe-AgSbTe2 (TAGS) compounds are promising thermoelectric materials.

Purpose of the Study:

• To investigate the thermoelectric properties of (GeTe)(x)(AgSbTe(2))(100-x) compounds (TAGS-x) as a function of temperature.
• To correlate microstructure with thermoelectric performance.
• To understand the role of nanoscale features in thermal conductivity.

Main Methods:

• Temperature-dependent measurements of thermoelectric properties (Seebeck coefficient, electrical resistivity, thermal conductivity) from 300 K to 720 K.
• High-resolution transmission electron microscopy (HRTEM) for microstructural analysis.
• Selected area electron diffraction (SAED) for structural characterization.

Main Results:

• TAGS-75, TAGS-80, and TAGS-85 samples achieved a peak dimensionless figure of merit (ZT) of 1.53, 1.50, and 1.50, respectively, at 720 K.
• TAGS-90 exhibited a lower ZT of 0.50 at 720 K, attributed to high carrier concentration.
• Nanoscale domains (∼10 nm) were observed in high-ZT samples.
• Low lattice thermal conductivity was observed, potentially due to enhanced phonon scattering by nanoscale domains.

Conclusions:

• (GeTe)(x)(AgSbTe(2))(100-x) compounds exhibit excellent thermoelectric properties, reaching state-of-the-art ZT values.
• The presence of nanoscale domains is crucial for reducing lattice thermal conductivity.
• These findings suggest that nanostructuring is an effective strategy for improving thermoelectric materials.