Cation-Driven Vibrational Hierarchy in NaCdX (X = As, Sb) Thermoelectrics: From Static Insulation to Rattling-Like Dissipation
Pengfei Zhang, Shuwei Tang, Da Wan, Xiaodong Li, Peng Ai, Wanrong Guo, T. Yan, Yunzhuo Zhang, Qingshun Quinn Li, Shulin Bai
Abstract
In the current work, the crystal structure, phonon, electronic transport, and thermoelectric (TE) properties of NaCdX (X = As, Sb) compounds are systematically investigated through first-principles calculations, Boltzmann transport theory, and a two-channel model. The Na + ion in NaCdX (X = As, Sb) compounds vibrates along different directions due to the different X (X = As, Sb) lone-pair electrons. Consequently, a pronounced anisotropy is discovered for the lattice thermal conductivity. The synergistic effect of the lone-pair electrons of X (X = As, Sb) atoms and the “static insulation to rattling-like dissipation” properties of the Na + ion contribute to the low lattice thermal conductivities (0.52 and 0.55 W m –1 K –1 @ 600 K) of NaCdX (X = As, Sb) compounds. Additionally, the TE performance of the NaCdX (X = As, Sb) compounds is evaluated by considering the multicarrier scatterings. The p -type NaCdAs compound exhibits an optimal figure of merit ( ZT ) of 1.2, while the n -type NaCdSb compound demonstrates a high ZT of 2.1 at 600 K. The present work not only offers a fundamental insight of the transition from the “static insulation” to “rattling-like dissipation” in suppressing lattice thermal conductivity, but also reveals the excellent TE properties of n -type NaCdSb compound.