Atomic to nanoscale chemical fluctuations: The catalyst for enhanced thermoelectric performance in high-entropy materials.

High-entropy materials have expanded the frontier for discovering uncharted physicochemical properties. The phenomenon of chemical fluctuation is ubiquitous in high-entropy materials, yet its role in the thermoelectric field is often overlooked. Herein, we designed and synthesized a series of (Mg(0.94-n)Yb(0.26)Sr(0.26)Zn(m))(Mg(n)Cd(0.69)Zn(0.69-m)Na(x))(Sb(1.74)Ca(0.26)) samples characterized by ultrahigh configurational entropy. These samples exhibit a homogeneous single-phase structure at macroscopic and microscopic scales, yet display notable chemical fluctuations at the atomic to nanoscale. These fluctuations, along with the unusual atomic occupations, lead to an exceptionally low lattice thermal conductivity akin to that of amorphous materials. Combining the optimized carrier concentration and well-maintained carrier mobility, we ultimately achieved a high zT value of 1.2 at 750 kelvin, outperforming most previously reported AB(2)Sb(2)-type Zintls. This study underscores that the atomic to nanoscale chemical fluctuations are the crucial catalyst for the enhanced thermoelectric performance in high-entropy materials.