Discovery of multi-anion antiperovskites 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. 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 X₆NFSn₂ (X = 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 (<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 figures of merit (ZTs) of ∼1.9 and ∼2.3 at high temperatures. Our exploration of multi-anion antiperovskites X₆NFSn₂ (X = Ca, Sr) realizes the “phonon-glass, electron-crystal” concept within the antiperovskite structure.