Octahedral Tilt-DrivenPhase Transitions in BaZrS₃ Chalcogenide Perovskite

Chalcogenide perovskites are lead-free materials for potential photovoltaic or thermoelectric applications. BaZrS₃ is the most-studied member of this family due to its superior thermal and chemical stability, desirable optoelectronic properties, and low thermal conductivity. Phase transitions in BaZrS₃ remain underexplored in the literature, as most experimental characterizations of this material have been performed at ambient conditions where the orthorhombic <i>Pnma</i> phase is reported to be stable. In this work, we study the dynamics of BaZrS₃ across a range of temperatures and pressures using an accurate machine learning interatomic potential trained with data from hybrid density functional theory calculations. At 0 Pa, we find a first-order phase transition from the orthorhombic to tetragonal <i>I</i>4/<i>mcm</i> phase at 610 K, and a second-order transition from the tetragonal to the cubic <i>Pm</i>3̅<i>m</i> phase at 880 K. The tetragonal phase is stable over a larger temperature range at higher pressures. To confirm the validity of our model we compare our results with a range of published experimental data and report a prediction for the X-ray diffraction pattern as a function of temperature.