Doping strategy in metavalently bonded materials for advancing thermoelectric performance

Area of Science:

• Materials Science
• Solid-State Chemistry
• Condensed Matter Physics

Background:

• Metavalent bonding yields exceptional properties in thermoelectric, phase-change, and optoelectronic materials.
• Doping metavalent materials is key to tuning charge and phonon transport for improved thermoelectric performance.
• Predicting dopant behavior (solid solution vs. secondary phase) is challenging, hindering material property tailoring.

Purpose of the Study:

• To propose and demonstrate a strategy for predicting and controlling dopant behavior in metavalent systems.
• To investigate the formation of solid solutions versus secondary phases in metavalent GeTe alloys.
• To enhance thermoelectric properties through controlled doping.

Main Methods:

• Alloying metavalent GeTe with various sulfides (PbS, GeS, SnS).
• Analyzing the resulting microstructures to determine dopant incorporation (solid solution or secondary phase).
• Characterizing the thermoelectric transport properties of the synthesized materials.

Main Results:

• Solid solutions formed when alloying GeTe with metavalent PbS, while secondary phases formed with covalently bonded GeS and SnS.
• Alloying GeTe with PbS reduced phonon propagation and optimized electrical transport.
• A high figure-of-merit (ZT) of 2.2 at 773 K was achieved in (Ge$_{0.84}$Sb$_{0.06}$Te$_{0.9}$)(PbSe)$_{0.05}$(PbS)$_{0.05}$ due to these effects.

Conclusions:

• Solid solution formation is favored in metavalent-metavalent systems, while precipitates are more likely in metavalent-covalent systems.
• This understanding enables rational design of microstructures and properties in metavalent materials.
• The strategy is applicable for designing advanced thermoelectric materials and potentially other functional materials.