Precision Interface Engineering by ALD in CuNi Alloys Towards High Thermoelectric Performance

Phase boundaries play a critical role in the carrier/phonon transport in thermoelectric materials. Herein, a novel technique for surface engineering of thermoelectric materials based on powder atomic layer deposition (pALD) of single/multi-layers of second phase on CuNi powders is presented. Ultrathin layers of various oxides (10–100 cycles of ZnO and Al₂O₃) are uniformly formed on the surface of CuNi alloy particles to validate or refute this idea. The formation of energy barriers and hierarchical interface modifications emerge from the deposition of ZnO/Al₂O₃ layers, leading in a considerable increase in the Seebeck coefficient. Although there is a slight decrease in electrical conductivity after 50 ALD cycles of ZnO, the increased Seebeck coefficients compensate for the loss and result in a 45% increase in power factor when compared to the pristine sample. In addition, the ZnO/Al₂O₃/ZnO multilayer structure was designed to improve electrical resistance at phase boundaries. In coatings with a high cycle number of samples (&gt; 25 cycles ZnO/5 cycles Al₂O₃/ 25 cycles ZnO cycles), the multi-layer structure retained an enhanced power factor while dramatically reducing heat conductivity. At 673 K, a maximum figure of merit (<i>zT</i>) of 0.22 was attained in 44 cycles ZnO/11 cycles Al₂O₃/ 44 cycles ZnO cycles multi-layer samples. When compared to pure CuNi, the <i>zT</i> value increased 144% due to pALD decoupling of thermoelectric parameters, which is comparable to the highest value ever recorded. The pALD technique to surface modification may readily be extended to different thermoelectric materials, assisting in the creation of high-performance thermoelectric materials.