Germanium Vacancy Release and Atomic Off-Centering Engineering for Advanced GeTe Thermoelectrics

Area of Science:

• Materials Science
• Solid State Physics
• Nanotechnology

Background:

• Germanium telluride (GeTe) is a promising thermoelectric material for medium temperatures.
• High carrier concentrations due to Ge vacancies limit GeTe performance.
• Current methods to reduce vacancies compromise phonon scattering.

Purpose of the Study:

• To improve GeTe thermoelectric performance by engineering Ge vacancies and atomic off-centering.
• To investigate the effects of CdTe and ZnTe alloying on GeTe structure and properties.
• To achieve high dimensionless figure of merit (zT) and mechanical hardness.

Main Methods:

• Alloying GeTe with CdTe and ZnTe to create vacancy clusters and hierarchical precipitates.
• Inducing local off-centering of Ge atoms for enhanced phonon coupling and lattice strain.
• Analyzing band structure modifications including bandgap widening and impurity bands.

Main Results:

• Achieved peak dimensionless figure of merit (zT) values of ~2.2 and ~2.1 at 723 K for CdTe and ZnTe alloys, respectively.
• Obtained average zT values of ~1.4 and ~1.2 over 323-723 K.
• Demonstrated Vickers hardness exceeding 235 HV, indicating enhanced mechanical properties.
• Successfully reduced thermal conductivity through local structural engineering.

Conclusions:

• Ge vacancy release and atomic off-centering engineering are effective strategies for high-performance GeTe thermoelectrics.
• CdTe/ZnTe alloying offers a pathway to simultaneously enhance thermoelectric efficiency and mechanical stability.
• This local structural strategy presents a promising approach for advancing thermoelectric materials.