Diffusons-Driven Thermal Transport and Band Convergence in Zintl-Phase BaZn ₂ <i>X</i> ₂ ( <i>X</i> = P, As) Thermoelectric Materials

First-principles calculations combined with a two-channel model are employed to investigate the thermoelectric properties of Zintl-phase BaZn2X2 (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 BaZn2P2 and BaZn2As2 compounds at 900 K, respectively. Notably, the BaZn2As2 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 BaZn2As2 compound achieves a maximum dimensionless figure of merit (ZTmax) 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.