Entropy-Stabilized Diamondoid AgCdInSe ₃ with Ultralow Thermal Conductivity and High Carrier Mobility for Thermoelectrics

Recently, diamondoid thermoelectric materials have attracted widespread attention owing to their unique transport properties and high lattice compatibility, which provide a promising platform for simultaneously tuning electron and phonon transport through compositional modulation. Although entropy engineering has been widely employed in rock-salt thermoelectric materials to suppress thermal conductivity, its application in diamondoid compounds remains rare. This is mainly because most diamondoid materials intrinsically exhibit low electrical conductivity, while highly disordered atomic arrangements often degrade carrier mobility, thereby suppressing electronic transport. Herein, we report the discovery of a new wurtzite-type diamondoid material, AgCdInSe₃, realized through entropy engineering. Crystallographic analysis combined with transmission electron microscopy reveals mixed occupation of all cation sites accompanied by local lattice distortion, resulting in an ultralow thermal conductivity of ∼0.3 W m^-1 K^-1 in AgCdInSe₃. Remarkably, despite the highly disordered atomic structure, AgCdInSe₃ exhibits a simple and light conduction band with an effective mass of 0.2 m₀, enabling a relatively high room-temperature carrier mobility of 285 cm² V^-1 s^-1. Consequently, the optimized Ag_0.977Cd_1.02In_1.003Se₃ achieves a peak <i>ZT</i> of 1.2 at 873 K, and the corresponding single-leg device delivers a power density of 1383 W m^-2 under a Δ<i>T</i> = 500 K, highlighting the potential of this material as a new n-type diamondoid thermoelectric.