In the quest for sustainable energy solutions, thermoelectric materials have long been a beacon of hope. These materials can directly convert heat into electricity, offering a clean and efficient way to harness waste heat from various industrial processes. Among these, Mg2(Si,Sn) has emerged as a strong contender, composed of abundant, non-toxic, and cost-effective elements. However, a recent study published in ‘Small Science’ has uncovered a significant challenge that could impact its large-scale application.
The research, led by Amandine Duparchy at the Institute of Materials Research at the German Aerospace Center (DLR) in Cologne, Germany, reveals that the thermal stability of n-type Mg2(Si,Sn) may be compromised even at room temperature. This finding could have profound implications for the energy sector, where the stability of materials is crucial for long-term performance and reliability.
The study employed a suite of advanced techniques, including integral thermoelectric properties measurements, locally resolved Seebeck coefficient analysis, scanning electron microscopy/energy-dispersive X-ray spectroscopy, and atomic force microscopy. These methods were used to assess changes in n-type samples stored in ambient atmosphere for years. The results were striking: the diffusion of loosely bound magnesium from the bulk towards the surface, followed by oxidation, led to a degradation of the material’s thermoelectric performance.
Duparchy explains, “We found that the diffusion of magnesium is a critical factor in the degradation process. This diffusion occurs mainly via magnesium vacancies, which are more prevalent in Sn-rich Mg2(Si,Sn).” This microscopic mechanism was further supported by first-principles calculations, which showed that magnesium diffusivity in Mg2(Si,Sn) is high at room temperature.
The implications of this research are significant for the energy sector. Thermoelectric generators, which convert waste heat into electricity, could see their efficiency and lifespan reduced if the material degrades over time. This could hinder the widespread adoption of thermoelectric technologies, which are crucial for improving energy efficiency and reducing carbon emissions.
However, the study also opens up new avenues for research. Understanding the mechanisms behind magnesium diffusion and oxidation could lead to the development of more stable thermoelectric materials. As Duparchy notes, “Our findings highlight the need for further research into stabilizing Mg2(Si,Sn) and other similar materials. This could involve exploring different compositions or adding stabilizing elements to reduce magnesium diffusion.”
The research, published in ‘Small Science’ (translated from German as ‘Small Science’), underscores the importance of material stability in the development of advanced thermoelectric technologies. As the energy sector continues to seek sustainable and efficient solutions, the insights gained from this study could pave the way for future innovations in thermoelectric materials.