Diffuson-driven lattice thermal conductivity in Zintl arsenides: disrupting mass-thermal conductivity relation for high thermoelectric performance

Zintl compounds of the Ca14AlSb11 structure type, especially Yb14MSb11 (M = Mg, Mn, Zn), have emerged as leading contenders for high-temperature thermoelectric applications because of their very low thermal conductivity and excellent electronic properties. In comparison, the lighter arsenic-based compounds have received less attention, as they are generally thought to have poor thermoelectric performance due to higher thermal conductivity. In this study, we synthesized 4 compounds, Eu14MAs11 (M = Mg, Zn, Cd) and Eu14Zn1.2As11, and refined their powder diffraction patterns using Rietveld refinement. We measured the transport properties of these compounds to demonstrate that diffuson conduction is common across these compositions, resulting in a lattice thermal conductivity of about 0.55 W m-1 K-1 at 298 K and challenging the usual relationship between mass and lattice thermal conductivity. The combination of low thermal conductivity and high valley degeneracy enables these materials to reach impressive thermoelectric performance, with Eu14MgAs11 achieving a maximum zT of 1.3 at 1250 K.