Isotope effect of thermopower in the TTFCOONH₃Ph single crystal

The thermopowers of single-crystalline anilinium tetrathiafulvalene-2-carboxylate (TTFCOONH₃Ph) and its deuteriated form (TTFCOOND₃Ph) have been examined at room temperature, and a significant isotope effect was found: 102 μV/K for TTFCOONH₃Ph, and 48 μV/K for TTFCOOND₃Ph, which amounts to a difference of a factor of around two. The origin of the difference, for example, X-ray crystal structure and doping level, was examined based on chemical and physical characterizations, and it was found that very low ion transport drastically enhances the thermopower of holes, giving rise to the large isotope effect. A large isotope effect of thermopower has been found for semiconducting TTFCOONH₃Ph and its deuteriated form, TTFCOOND₃Ph. The origin of the isotope effect has been investigated based on chemical and physical characterizations using high-quality single crystals.