Ultra-Low Thermal Conductivity and Promising Thermoelectric Performance in the Structurally Complex Zintl Phase: Eu14GaAs11

Abstract

Intermetallic Zintl compounds of the Ca14AlSb11 (14-1-11) structure type are intriguing materials for study due to their small bandgap semiconducting behavior and exceptionally low thermal conductivity. Eu14GaAs11 is a new member of the family, containing zero-dimensional tetrahedral [GaAs4]9- subunits. This compound crystallizes in the tetragonal crystal system of I4 1 /acd space group, similar to other 14-1-11 compounds. Eu14GaAs11 has been characterized as a semiconductor with a bandgap of 0.61 eV, as calculated using the Goldsmid-Sharp formula. Electronic transport measurements indicate a high Seebeck coefficient of 232 µV/K at 321 K, peaking at 424 µV/K at 713 K. The electrical resistivity is particularly high due to low carrier concentrations. However, the compound's notable strengths include its stability at high temperatures and its ultra-low thermal conductivity of 0.59 W m⁻¹ K⁻¹ at room temperature, with minimal electronic contribution, making it even lower than that of other high-performing Zintl phases. Given its low thermal conductivity and high Seebeck coefficient, Eu14GaAs11 presents potential for further optimization by adjusting the carrier concentration to enhance its thermoelectric performance.