The team creates crystals that generate electricity from heat

To convert heat into electricity, readily available materials from harmless raw materials open new perspectives in the development of safe and inexpensive so-called “thermoelectric” materials. A synthetic copper mineral acquires complex structure and microstructure through simple changes in its composition, laying the groundwork for desired properties, according to a study published in the journal applied chemistry.

The new synthetic material is composed of copper, manganese, germanium and sulphur, and it is produced through a fairly simple process, explains materials scientist Emmanuel Guilmeau, CNRS researcher at the CRISMAT laboratory, Caen, France, who is the corresponding author of the study. . “The powders are simply mechanically alloyed by ball milling to form a pre-crystallized phase, which is then densified at 600 degrees Celsius. This process can be easily extended,” he says.

Thermoelectric materials convert heat into electricity. This is particularly useful in industrial processes where waste heat is reused as valuable electrical energy. The opposite approach is the cooling of electronic components, for example, in smartphones or cars. The materials used in this type of application must not only be effective, but also inexpensive and, above all, safe for health.

However, the thermoelectric devices used to date use expensive and toxic elements such as lead and tellurium, which offer the best conversion efficiency. To find safer alternatives, Emmanuel Guilmeau and his team turned to derivatives of natural copper-based sulphide minerals. These mineral derivatives are mainly composed of non-toxic and abundant elements, and some of them have thermoelectric properties.

Today, the team has successfully produced a series of thermoelectric materials featuring two crystal structures within a single material. “We were very surprised with the result. Usually, changing the composition slightly has little effect on the structure in this class of materials,” says Emmanuel Guilmeau, describing their discovery.

The team found that replacing a small fraction of the manganese with copper produced complex microstructures with interconnected nanodomains, defects and coherent interfaces, which affected the material’s transport properties for electrons and heat.

Emmanuel Guilmeau says the new material produced is stable up to 400 degrees Celsius, a range well within the waste heat temperature range of most industries. He is convinced that, based on this discovery, new and cheaper non-toxic thermoelectric materials could be designed to replace the more problematic materials.