Cation Modulation in AgSbTe₂ Realizes Carrier Optimization, Defect Engineering, and a 7% Single-Leg Thermoelectric...

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Silver antimony telluride (AgSbTe₂) is crucial for mid-temperature thermoelectric generators (TEGs).
• Cation manipulation is a key strategy for improving AgSbTe₂ performance.
• Optimizing thermoelectric properties requires balancing power factor and thermal conductivity.

Purpose of the Study:

• To enhance the thermoelectric performance of AgSbTe₂ through cation modulation.
• To investigate the effects of germanium (Ge) incorporation on the material's properties.
• To establish structure-property relationships for improved thermoelectric devices.

Main Methods:

• Synthesis of off-stoichiometric and germanium-doped AgSbTe₂ crystals.
• Characterization using X-ray Photoelectron Spectroscopy (XPS) for chemical states.
• Transmission Electron Microscopy (TEM) for structural analysis (superlattices, defects).
• Measurement of thermoelectric transport properties (Seebeck coefficient, electrical conductivity, thermal conductivity).

Main Results:

• Achieved a peak thermoelectric figure of merit (zT) of 1.5 at 583 K in Ag₁.₀₄Sb₀.₉₆Te₂.
• Incorporation of Ge led to increased carrier concentration (n<0xE2><0x82><0x99>) and revealed Ge⁴⁺, Ag⁺, Sb³⁺ states via XPS.
• Observed superlattice structures and linear defects in TEM, reducing lattice thermal conductivity (κ<0xE2><0x82><0x97>).
• Ag₁.₀₂Ge₀.₀₂Sb₀.₉₆Te₂ exhibited a peak zT of 1.77 at 623 K.
• A single-leg TEG device achieved 7% conversion efficiency with a 350 K temperature gradient.

Conclusions:

• Cation modulation, specifically Ge doping, effectively enhances the thermoelectric performance of AgSbTe₂.
• The improved zT results from a synergistic effect of enhanced power factor and reduced lattice thermal conductivity.
• The study confirms the link between material defects, transport properties, and thermoelectric efficiency.