Discovery of Multi-Anion Antiperovskite X₆NFSn₂ (X = Ca, Sr) as Promising Thermoelectric Materials by Computational Screening

The thermoelectric performance of existing perovskites lags far behind that of state-of-the-art thermoelectric materials such as SnSe.^{[1], [2]} Despite halide perovskites showing promising thermoelectric properties, namely, high Seebeck coefficients and ultralow thermal conductivities, their thermoelectric performance is significantly restricted by low electrical conductivities. Here, we explore new multi-anion antiperovskites <i>X</i>₆NFSn₂ (<i>X</i> = Ca, Sr and Ba) via B-site anion-mutation in antiperovskite and global structure searches, and demonstrate their phase stability by first-principles calculations. Ca₆NFSn₂ and Sr₆NFSn₂ exhibit decent Seebeck coefficients and ultralow lattice thermal conductivities (&lt; 1 W m⁻¹ K⁻¹). Notably, Ca₆NFSn₂ and Sr₆NFSn₂ show remarkably larger electrical conductivities compared to the halide perovskite CsSnI₃. The combined superior electrical and thermal properties of Ca₆NFSn₂ and Sr₆NFSn₂ lead to high thermoelectric figure of merit <i>ZT</i> ~ 1.9 and ~ 2.3 at high temperatures. Our exploration of multi-anion antiperovskites <i>X</i>₆NFSn₂ (<i>X</i> = Ca, Sr) realizes the “phonon-glass, electron-crystal" concept within the antiperovskite structure.^[3]<br/><br/>[1] Zhou C, Lee Y K, Yu Y, et al. Nature materials, 2021, 20(10): 1378-1384.<br/>[2] Lee W, Li H, Wong A B, et al. Proceedings of the National Academy of Sciences, 2017, 114(33): 8693-8697.<br/>[3] Han D, Zhu B, Cai Z, Spooner B, Rude S, Schnick W, Bein T, Scanlon D and Ebert H, Matter., 2023, submitted.