Silver Atom Off-Centering in Diamondoid Solid Solutions Causes Crystallographic Distortion and Suppresses Lattice Thermal Conductivity.

The class I-III-VI diamondoid compounds with tetrahedral bonding are important semiconductors widely applied in optoelectronics. Understanding their heat transport properties and developing an effective method to predict the diamondoid solid solutions' thermal conductivity will help assess their impact as thermoelectrics. In this work, we investigated in detail the heat transport properties of CuGaInTe and CuAgGaTe and found that in the Ag-alloyed solid solutions, the Ag atom off-centering effect results in crystallographic distortion and extra strong acoustic-optical phonon scattering and an extremely low lattice thermal conductivity. Moreover, we integrate the alloy scattering and the off-centering effect with the crystallographic distortion parameter to develop a modified Klemens model that predicts the thermal conductivity of diamondoid solid solutions. Finally, we demonstrate that CuAgGaTe solid solutions are promising p-type thermoelectric materials, with a maximum of 1.23 at 850 K for CuAgGaTe.