Copper ion diffusion by solid solution treatment advancing GeTe-based thermoelectrics

Area of Science:

• Materials Science
• Solid-State Physics
• Nanotechnology

Background:

• Coinage metals like copper (Cu) and silver (Ag) are known dopants for thermoelectric materials, optimizing carrier concentration and mobility.
• Traditional doping methods, such as eutectic reactions, often lead to undesirable interstitial doping, creating lattice defects.

Purpose of the Study:

• To develop an innovative solid solution doping strategy for precise copper (Cu) ion incorporation into host lattice sites.
• To investigate the effects of targeted doping on lattice structure, defects, and thermoelectric properties of Germanium-Telluride (GeTe) based materials.

Main Methods:

• Utilized first-principles calculations and in-situ experimental techniques.
• Employed a solid solution doping strategy for targeted copper (Cu) ion substitution.
• Analyzed ion diffusion, lattice renormalisation, and defect reduction.

Main Results:

• Demonstrated that targeted doping exclusively places Cu ions on host lattice sites, avoiding interstitial positions.
• Observed lattice renormalisation, leading to reduced lattice defects and suppressed hole concentration.
• Achieved a high figure-of-merit (ZT) of 2.3 at 775 K for 1 at.% Cu doped Ge$_{0.85}$Sb$_{0.10}$Te, with an average ZT of 1.4 from 300-775 K.
• Reported a power density of 2.23 W·cm$^{-2}$ for a single-leg thermoelectric module.

Conclusions:

• The solid solution doping strategy offers a new pathway for creating high-quality thermoelectric materials with reduced defects and enhanced carrier mobility.
• Understanding the kinetics of dynamic doping is crucial for optimizing thermoelectric material performance.
• This approach enables precise control over dopant location, significantly improving thermoelectric efficiency.