Getting to distant planets for space exploration is only half the challenge—packing, transporting and generating energy for these missions requires highly specialized technologies. The 2015 film The Martian, for example, depicts the protagonist using a thermoelectric generator to fend off Mars’ unforgiving cold.
Such machines require thermoelectric materials to convert differences in temperature into electricity, or vice versa. They are used in the real world to power fridges and air-conditioning units and as compact energy sources for space probes and planetary rovers.
“Whether a thermoelectric material is practically useful largely depends on its device efficiency, which is determined by the material’s figure of merit, zT,” explained Jianwei Xu, a Senior Researcher at A*STAR’s Institute of Materials Research and Engineering (IMRE).
The utility of thermoelectric materials is influenced by their electrical and thermal conductivity. Additionally, some semiconductors undergo significant shifts in the organization of their molecules at different temperatures, a phenomenon that governs their thermoelectric potential.
Take germanium telluride (GeTe), which exists in two distinct phases: a rhombohedral phase at room temperature and a cubic phase at higher temperatures. The cubic phase is also associated with a lower thermal conductivity and therefore higher zT values. Together with co-corresponding author Gang Zhang, a Senior Scientist at A*STAR’s Institute of High Performance Computing (IHPC), Xu explored how chemical modifications could lock GeTe in the cubic phase, thus boosting its electricity generating capabilities.
The team mixed GeTe with precise amounts of elemental tin in a process known as alloying. Their new GeTe alloy was held at the pure cubic phase which elevated its zT considerably. The idea of generating a GeTe alloy was sparked by combining thermoelectrics and ferroelectrics, materials that have reversible electrical poles.
“Having worked on ferroelectric materials, in which tuning phase transition temperature is important, we applied some of the knowledge from ferroelectric materials to tune the phase transition temperature in GeTe,” said Ady Suwardi, a Scientist at A*STAR’s Institute of Materials Research and Engineering (IMRE). This study, the first of its kind, demonstrates how cross-domain knowledge between thermoelectric and ferroelectric materials can drive scientific advancements, Suwardi shared.
Follow-up studies aim to further fine-tune GeTe, a brittle material that is prone to cracking after repeated use cycles in a generator. “We are now actively working to enhance the mechanical robustness of this material, which will be important before widespread commercial adoption,” Xu said. Reducing manufacturing costs by identifying less expensive substitutes for Ge will also be a priority moving forward, he added.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering (IMRE) and the Institute of High Performance Computing (IHPC).