Electronic structure, elastic and transport properties of the A2TtAs2 zintl phases (A = Rb, Cs; Tt = Si, Sn): A quantum computational approach

Using ab initio calculations and the Boltzmann transport theory, we examined the mechanical, electronic and transport properties of the tetrel-based Zintl phases A₂TtAs₂ (A = Rb, Cs; Tt = Si, Sn). Density functional theory calculations yielded highly accurate structural parameters that were well within appropriate tolerance levels. TB-mBJ calculations predicted band gaps ranging from 1.65 to 1.89 eV. Silicon compounds have larger band gaps than tin compounds, primarily due to shorter A-As and Tt-As bond lengths. Topological analysis shows mixed ionic-covalent bonding, with stronger Si-As covalent bonds in silicon-based compounds. According to the quantum theory of atoms in molecules, the mechanical response is primarily determined by the strength of the Tt-As bonding. The predicted low phonon velocity and marked lattice anharmonicity indicate ultra-low lattice thermal conductivity. Similar transport properties are observed within compounds based on the same tetrel element. Our findings predict promising underlying electronic transport properties and thermoelectric performance. Thus, A₂TtAs₂ compounds are potential n-type high-temperature thermoelectric materials.