Diffusons-Driven Thermal Transport and Band Convergence in Zintl-Phase BaZn <sub>2</sub> <i>X</i> <sub>2</sub> ( <i>X</i> = P, As) Thermoelectric Materials
Pengfei Zhang, Zhanpeng Xu, Shuwei Tang, T. F. Zheng, Da Wan, Peng Ai, T. Yan, Shiyan Pei, Yufei Meng, Shulin Bai
Abstract
High Resolution Image Download MS PowerPoint Slide First-principles calculations combined with a two-channel model are employed to investigate the thermoelectric properties of Zintl-phase BaZn 2 X 2 ( X = P, As) compounds in the present work. Although crystallizing in a three-dimensional (3D) crystal structure, these materials exhibit unique one-dimensional (1D) transport characteristics due to the covalently bonded [Zn– X ] − ( X = P, As) anionic framework and loosely bound Ba atom that occupy channels along the x -axis direction. Such a structural motif yields highly anisotropic carrier transport, with significantly enhanced power factors along the x -axis direction. Simultaneously, the weak interaction between the Ba atom and the [Zn– X ] − ( X = P, As) anionic framework promotes phonon scattering, leading to low lattice thermal conductivities of 1.19 and 0.73 W m –1 K –1 for BaZn 2 P 2 and BaZn 2 As 2 compounds at 900 K, respectively. Notably, the BaZn 2 As 2 compound exhibits conduction band convergence, forming a multivalley electronic structure that improves the balance between carrier mobility and effective mass, thereby enhancing carrier transport performance under n -type doping circumstance. As a result, the n -type doping BaZn 2 As 2 compound achieves a maximum dimensionless figure of merit ( ZT max ) value of 1.07 at 900 K. These findings not only offer a universal theoretical framework for the accurate prediction of lattice thermal conductivity in strongly anharmonic materials but also establish theoretical principles for the design of high-performance thermoelectric materials with 1D transport characteristics within 3D crystal structures.