A research team from Skoltech, Ben-Gurion University of the Negev, N.M. Emanuel Institute of Biochemical Physics RAS, and other scientific organizations has studied the effect of various types of defects on the mechanical behavior of lead telluride (PbTe)-based thermoelectric material. The material is widely used as a thermoelectric due to its high heat-to-electricity conversion efficiency, but its high brittleness remains a key limitation that significantly restricts practical applications. The results were published in the Journal of Materials Chemistry A.
In lead telluride, there are three main types of defects: atomic substitutions, displacement of one element to another’s position, and formation of voids (vacancies) when individual tellurium or lead atoms are missing from the structure. In the first case, lead or tellurium atoms are randomly replaced by other elements (such as sodium or bismuth). The purpose of such substitutions is to modify the material’s electrical properties to improve device efficiency. However, these substitutions also affect the material’s mechanical strength.
When a substituting atom has a different number of valence electrons than the host atom, it creates either an electron excess or deficiency, thereby modifying the material’s electrical conductivity. This creates two possible conductivity types: n-type, where free electrons dominate, and p-type, where positively charged carriers (holes) prevail.
“Lead telluride is a very promising material, but the problem is that p-type is best for electronics while having worse mechanical properties. Our task was to find a way to improve these properties of p-doped lead telluride. In the paper, we showed how this can be addressed through the material’s internal defects. This approach opens prospects for developing effective next-generation thermoelectrics that combine high energy conversion efficiency with improved performance characteristics,” commented the study’s first author Ilya Chepkasov, a senior research scientist at the Skoltech Energy Transition Center.
The authors investigated mechanisms for modifying the material’s mechanical properties by introducing specific defects, including various types of substituents, vacancies, and interstitials. They employed a comprehensive set of modern theoretical modeling methods, including density functional theory calculations, chemical bonding analysis using the Crystal Orbital Hamilton Population (COHP) method, and computer deformation simulations using deep learning-based interatomic potential models.
“Our calculations show significant increases in material brittleness for sodium-doped (p-type) samples with tellurium vacancies, which are intrinsic defects in lead telluride. A similar situation occurs when silver and copper interstitials (n-type) coexist with lead vacancies,” shared Professor Alexander Kvashnin from the Skoltech Energy Transition Center and co-author of the study.
The key factor affecting brittleness and plasticity in doped lead telluride with different defect types is the excess or deficiency of electron density in PbTe’s chemical bonds. Deep learning neural network simulations identified optimal tuning mechanisms to improve the doped material’s mechanical properties. For instance, sodium-doped material can be made more ductile by adding lead vacancies and substituting some lead with tellurium.
The results make an important contribution to developing high-performance lead telluride-based thermoelectric generators and address its main limitation — excessive mechanical brittleness.
