AUTHOR=Chang Zheng , Ma Jing , Yuan Kunpeng , Zheng Jiongzhi , Wei Bin , Al-Fahdi Mohammed , Gao Yufei , Zhang Xiaoliang , Shao Hezhu , Hu Ming , Tang Dawei TITLE=Zintl Phase Compounds Mg3Sb2−xBix (x = 0, 1, and 2) Monolayers: Electronic, Phonon and Thermoelectric Properties From ab Initio Calculations JOURNAL=Frontiers in Mechanical Engineering VOLUME=8 YEAR=2022 URL=https://www.frontiersin.org/journals/mechanical-engineering/articles/10.3389/fmech.2022.876655 DOI=10.3389/fmech.2022.876655 ISSN=2297-3079 ABSTRACT=

The Mg₃Sb_2−xBi_x family has emerged as the potential candidates for thermoelectric applications due to their ultra-low lattice thermal conductivity (κL) at room temperature (RT) and structural complexity. Here, using ab initio calculations of the electron-phonon averaged (EPA) approximation coupled with Boltzmann transport equation (BTE), we have studied electronic, phonon and thermoelectric properties of Mg₃Sb_2−xBi_x (x = 0, 1, and 2) monolayers. In violation of common mass-trend expectations, increasing Bi element content with heavier Zintl phase compounds yields an abnormal change in κL in two-dimensional Mg₃Sb_2−xBi_x crystals at RT (∼0.51, 1.86, and 0.25 W/mK for Mg₃Sb₂, Mg₃SbBi, and Mg₃Bi₂). The κL trend was detailedly analyzed via the phonon heat capacity, group velocity and lifetime parameters. Based on quantitative electronic band structures, the electronic bonding through the crystal orbital Hamilton population (COHP) and electron local function analysis we reveal the underlying mechanism for the semiconductor-semimetallic transition of Mg₃Sb_2-−xBi_x compounds, and these electronic transport properties (Seebeck coefficient, electrical conductivity, and electronic thermal conductivity) were calculated. We demonstrate that the highest dimensionless figure of merit ZT of Mg₃Sb_2−xBi_x compounds with increasing Bi content can reach ∼1.6, 0.2, and 0.6 at 700 K, respectively. Our results can indicate that replacing heavier anion element in Zintl phase Mg₃Sb_2−xBi_x materials go beyond common expectations (a heavier atom always lead to a lower κL from Slack’s theory), which provide a novel insight for regulating thermoelectric performance without restricting conventional heavy atomic mass approach.