Thermal effects on the structure and electronic band gap of the needle-like and distorted perovskite phases of SrZrS3 were investigated over the temperature range 300–1200 K by means of ML-accelerated ab initio molecular dynamics in an NPT ensemble.

Chalcogenide perovskites (CPs), with the general composition ABX3, where A and B are metals and X = S and Se, have recently emerged as promising materials for application in photovoltaics. However, the development of CPs and their applications has been hindered by the limitations of available preparation methods. Here we present a new approach for the synthesis of CPs, based on the sulfurization of ternary and binary oxides or carbonates with in situ formed boron sulfides. In contrast to the previously described approaches, the method presented here uses chemically stable starting materials and yields pure-phase crystalline CPs within several hours, under low hazard conditions. CP yields over 95% are obtained at temperatures as low as 600 °C. The generality of the approach is demonstrated by the preparation of CPs with compositions BaZrS3, β-SrZrS3, BaHfS3, SrHfS3, and EuHfS3. Mechanistic insights about the formation of CPs are discussed.

The effects of temperature and composition on the structural and electronic properties of chalcogenide perovskite (CP) materials AZrX3 (A = Ba, Sr, Ca; X = S, Se) in the distorted perovskite (DP) phase are investigated using ab initio molecular dynamics (AIMD) accelerated by machine-learned force fields. Long-range van der Waals (vdW) interactions, incorporated into the Perdew–Burke–Ernzerhof (PBE) exchange–correlation functional using the DFT-D3 scheme, are found to be crucial for achieving correct predictions of structural parameters. Our calculations show that the distortion of the DP structure with respect to the parent cubic (C) phase, realized in the form of interoctahedral tilting, decreases with the increasing size of the A cations. The tendency for a gradual transformation of the DP-to-C phase with increasing temperature is shown to be strongly composition-dependent. The transformation temperature decreases with the size of cation A and increases with the size of anion X. Thus, within the range of the temperatures considered here (300–1200 K), a complete transformation is observed only for BaZrS3 (∼600 K) and BaZrSe3 (∼900 K). The computed band gap of CPs is shown to monotonically decrease with increasing temperature, and the magnitude of this decrease is found to be proportional to the extent of the thermally induced changes in the internal structure. Diverse factors affecting the magnitude of band gaps of CP materials are analyzed.