High‐Pressure and High‐Temperature Dion–Jacobson Layered Perovskite Polymorphs of KWO3F.

Two new Dion–Jacobson layered perovskite polymorphs of the known oxyfluoride compound KWO3F are reported. A high‐pressure modification was synthesized using a multianvil setup and subsequently transformed into a high‐temperature phase at ∼311 °C. The crystal structures of both polymorphs were determined by use of single‐crystal X‐ray diffraction and are described in detail herein. Differential thermal analyses and thermogravimetric analyses were carried out to further investigate the phase transition characteristics. Bond valence (BV) and charge distribution (CHARDI) calculations confirm the occupancy of mixed O|F anion positions, and Rietveld refinements as well as MAPLE calculations support the structure models. [ABSTRACT FROM AUTHOR]