Researchers have unveiled the impressive thermoelectric properties of single-crystalline TiCoSb-based half-Heusler materials, setting new benchmarks for energy conversion efficiency. This breakthrough could pave the way for more effective thermoelectric applications, potentially enabling more sustainable energy harvesting technologies.
Half-Heusler compounds have garnered attention for their capabilities to directly convert thermal energy to electricity, making them appealing candidates for application in automotive, industrial waste heat recovery, and portable power generation. The latest study showcases how high-quality single crystals of these materials outperform their polycrystalline counterparts, primarily due to enhanced electron transport properties.
Traditionally, thermoelectric materials suffered from defects associated with polycrystalline forms, which hamper their efficiency by scattering electrons. The authors of the article, through their rigorous research and application of the flux method, successfully synthesized single-crystalline TiCoSb samples larger than one centimeter. They achieved significant advancements by leveraging improved electron mobility and lowered defect levels.
Central to their research was the co-doping process using niobium (Nb) and tantalum (Ta), which optimized the electron concentration effectively. This tuning resulted not only in enhanced electrical properties but also contributed positively to the overall thermoelectric performance. The crystals exhibited an average power factor of approximately 37 μW cm-1 K-2 across temperatures ranging from 307 K to 973 K.
Further investigation revealed the role of hafnium (Hf) alloying, which bolstered anharmonic scattering rates, thereby significantly reducing lattice thermal conductivity. This reduction was particularly beneficial, as thermal conductivity is often a barrier to achieving high thermoelectric performance. The crystallographic structure was assessed accurately, and rocking curve measurements showed exceptionally low levels of mosaicity, confirming the high quality of the grown crystals.
“Our findings reveal the promise of TiCoSb-based single crystals for thermoelectric power generation,” noted the researchers. The materials also achieved remarkable peak figures of merit (zT), with values greater than one, showcasing their exceptional conversion efficacy. Notably, the TiCoSb-based single crystals demonstrated about 10.2% energy conversion efficiency when subjected to temperature gradients of 700 K.
The experimentation process involved careful manipulation of growth parameters, underlining how delicate any equilibrium system becomes with potential formation of unstable phases during synthesis. The results reflect reduced resistivity with increasing Nb concentrations and improved electrical conductivity overall, illustrating the effectiveness of their doping approach. The research compared these results systematically against existing polycrystalline data, underlining the significant improvements.
Significantly, the authors noted how the power factor diminished slightly with increasing temperatures, primarily due to increased electron-phonon interactions. This insight highlights important avenues for future research, particularly around optimizing the stoichiometry and leveraging non-equilibrium growth techniques to push the boundaries of thermoelectric performance.
By providing concrete advancements and demonstrating the clear benefits of utilizing single crystals, this work illuminates promising pathways for developing next-generation thermoelectric devices and enhances our overall approach toward combating energy loss and sustainability challenges.
These new revelations provide not only scientifically significant data but also lay the groundwork for future explorations of TiCoSb-based materials across various applications, potentially transforming sustainable energy solutions.