They found that they contain regions with different atomic compositions and that these influence its thermal conductivity.
Thermoelectric energy recovery involves converting waste heat into useful electrical energy. It is a promising technology that could make a significant contribution to the net-zero goal. However, many of the high-performance thermoelectric materials contain scarce elements such as tellurium. This means that there is a drive to search for alternative materials that contain environmentally friendly and Earth-abundant elements instead.
In this study, published in Journal of the American Chemical Society (JACS), the group of researchers from the University of Reading and ISIS focussed on a sulfide, as sulfur is a very abundant element. They studied the effect of decreasing the Pb2+ and Cu+ content on the crystal structure and properties of the thermoelectric material Cu1–x□xPb1–xBi1+xS3 for x = 0, 0.33, 0.6 and 0.83.
“Understanding the relationship between crystal structure, bonding and thermal transport is critical for the discovery of materials with ultralow thermal conductivities," explains first author Paz Vaqueiro, from the University of Reading.
For many structural investigation techniques, Pb2+ and Bi3+ are almost indistinguishable as they have the same number of electrons. However, for neutrons, which interact directly with the nucleus, they have a significant contrast making neutrons the ideal tool to study crystal structures containing Pb2+ and Bi3+.
Their neutron diffraction data revealed that intermediate compositions crystallize in the krupkaite structure, instead of the aikinite structure taken by the x = 0 composition. Anna Herlihy (formerly at ISIS) performed the analysis of the pair distribution function (PDF) data, to investigate the local structure. The PDF analysis revealed that the disordering of vacancies (□) and cations deviates significantly from that expected for a statistical distribution.
This shows that, at a local level, copper-rich and copper-poor regions occur. The local interaction in these regions is likely to have an impact on the thermoelectric properties of the material.
“Our findings provide crucial insights into the effect of the local structure on the phonon transport," adds Paz. “This study highlights the potential of local-structure design to achieve high thermoelectric performance in crystalline solids. It is increasingly becoming apparent that “hidden" local atomic motifs within an average crystal structure can exert a dramatic influence on the lattice thermal conductivity."
This work was funded through a The Leverhulme Trust Research Project Grant awarded to Paz Vaqueiro, with co-investigator ISIS instrument scientist David Voneshen.
Further information
The full paper can be found at DOI: 10.1021/jacs.5c12526
