The many forms of entropy

In 2015 we co-authored two experimental papers, which dealt in one form or another with entropy effects albeit for very different systems. The first paper described a novel approach for increasing the solubility of fullerenes and other systems by increasing the configurational entropy, while the second paper dealt with the potential of high-entropy alloys as high-temperature thermoelectric materials.

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A group of researchers led by Christian Müller at the Chemistry Department of Chalmers demonstrated that the solubility of pristine fullerenes can be enhanced by mixing C60 and C70 thanks to the increase in configurational entropy of the ternary (C60-C70-solvent) system compared to the binary (C60-solvent) system. This “entropic dissolution” allows the preparation of field-effect transistors with an electron mobility of 1 cm2 V-1 s-1 and polymer solar cells with a highly reproducible power-conversion efficiency of 6%, as well as a thermally stable active layer. These results were published in a paper in Advanced Materials, which was highlighted on the cover of the issue.

In the second paper the potential of high-entropy alloys (HEAs) for thermoelectric applications was explored by a group that included researchers from three different departments at Chalmers. HEAs can be rather easily manufactured in large quantities and could in principle serve as high-temperature thermoelectrics. With this motivation, we explored for the first time systematically the thermoelectric properties of a series of HEAs. While the thus obtained figures-of-merit are still small, the large microstructural complexity and compositional variability of these systems highlight the possibility to exploit HEAs as a new class of future high temperature thermoelectrics. More details can be found in our publication in the Journal of Applied Physics, which was highlighted as an “Noteworthy Results in Materials Science”.

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