Origins of chalcogenide perovskite instability

TL;DR

This study investigates the stability challenges of chalcogenide perovskites, revealing that only a few compounds are both polymorphically and hull stable, and identifies key bonding interactions influencing their instability.

Contribution

The paper provides a comprehensive DFT-based analysis of 81 ABS3 compounds, elucidating the fundamental factors behind their polymorphic and hull instability, and compares stability models with experimental data.

Findings

Only BaZrS3 and BaHfS3 are fully stable among studied compounds.

Perovskite structures are stabilized by strong B-S covalent bonds.

Weaker inductive effects in sulfides explain their scarcity compared to oxides.

Abstract

Chalcogenide perovskites, particularly II-IV ABS3 compounds, are a promising class of materials for optoelectronic applications. However, these materials frequently exhibit instability in two respects: 1) a preference for structures containing one-dimensional edge- or face-sharing octahedral networks instead of the three-dimensional corner-sharing perovskite framework (polymorphic instability), and (2) a tendency to decompose into competing compositions (hull instability). We evaluate the stability of 81 ABS3 compounds using Density Functional Theory, finding that only BaZrS3 and BaHfS3 are both polymorphically and hull stable, with the NH4CdCl3-type structure being the preferred polymorph for 77% of these compounds. Comparison with existing tolerance factor models demonstrates that these approaches work well for known perovskites but overpredict stability for compositions without published experimental results. Polymorphic stability analysis reveals that perovskite structures are stabilized by strong B-S bonding interactions, while needle structures exhibit minimal B-S covalency, suggesting that electrostatic rather than covalent interactions drive the preference for edge-sharing motifs. Hull stability analysis comparing ABS3 to ABO3 analogues reveals a weaker inductive effect in sulfides as a possible explanation for the scarcity of sulfides compared with oxides. The relative instability of ABS3 compounds is further supported by experimental synthesis attempts. These findings provide fundamental insights into the origins of instability in chalcogenide perovskites and highlight the challenges in expanding this promising materials class beyond the few materials that have been reported to date.