Heat–Electric Power Conversion Without Temperature Difference Using Only n-Type Ba₈Au_xSi_46−x Clathrate with Au Compositional Gradient

Thermoelectric power generation is typically based on the Seebeck effect under a temperature gradient. However, the heat flux generated by the temperature difference results in low conversion efficiency. Recently, we developed a heat–electric power conversion mechanism using a material consisting of a wide-bandgap n-type semiconductor, a narrow-bandgap intrinsic semiconductor, and a wide-bandgap p-type semiconductor. In this paper, we propose a heat–electric power conversion mechanism in the absence of a temperature difference using only n-type Ba₈Au_xSi_46−x clathrate. Single-crystal Ba₈Au_xSi_46−x clathrate with a Au compositional gradient was synthesized by Czochralski method. Based on the results of wavelength-dispersive x-ray spectroscopy and Seebeck coefficient measurements, the presence of a Au compositional gradient in the sample was confirmed. It also observed that the electrical properties changed gradually from wide-bandgap n-type to narrow-bandgap n-type. When the sample was heated in the absence of a temperature difference, the voltage generated was approximately 0.28 mV at 500°C. These results suggest that only an n-type semiconductor with a controlled bandgap can generate electric power in the absence of a temperature difference.