The structural stability, damage tolerance, anisotropy and thermoelectric properties of ternary pnictides KYZ (Y=Mg, Zn, Cd; Z=P, Sb) from a first principles investigation

First-principles calculations were performed to investigate the structural stability, tensile stress-strain, anisotropy and thermoelectric properties of hexagonal KYZ (Y = Mg, Zn, Cd; Z = P, Sb) ternary pnictides. The thermodynamic stability of KYZ compounds was verified by negative formation energies. The absence of imaginary frequencies verifies the dynamical stability of KYZ compounds, except for KZnSb. Three-dimensional surface structure and 2D projections of mechanical moduli indicated the KYZ compounds have the higher anisotropy along xz plane than the xy plane. The stress-strain relationship of KYZ along the low-index [0001] and [11-20] directions is discussed. KZnP exhibits the highest tensile strength along the [0001] and [11-20] directions. Thermoelectric Seebeck coefficient (S), electrical conductivity (σ), power factor (PF) and electronic thermal conductivity (K e ) were calculated within the constant relaxation-time approximation. The lattice thermal conductivity (K L ) was estimated using the Slack model. The results show that all KYZ ternary pnictides possess intrinsically low lattice thermal conductivity. In particular, KCdSb has a K L of only 2.88 W/(m·K) at 300 K. The ZT increases with temperature for all ternary pnictides. Notably, under p-type doping conditions, KMgSb achieves a peak ZT value of 1.17 at 1000 K, while KCdSb reaches 0.99 at the same temperature, indicating their promising potential as high-temperature p-type efficient thermoelectric materials.