<i>A</i>CrF₃ Jahn–Teller-Distorted Fluoroperovskites: Expanding to RbCrF₃ and CsCrF₃

The Jahn-Teller effect significantly affects the CrF₆ octahedra in Cr(II) fluoroperovskites. Here, we report the synthesis, crystal structures, and magnetic properties of RbCrF₃ and CsCrF₃, thereby completing a comprehensive investigation of the <i>A</i>CrF₃ fluoroperovskites. Powder samples are prepared using a wet-chemical method, which allows stabilization of Cr(II). RbCrF₃ predominantly adopts the <i>P</i>4/<i>mbm</i> space group; however, the absence of the expected (211) peak suggests a limited correlation length, and we demonstrate that this is a result of stacking faults in the rotation of the distorted CrF₆ octahedra along the <i>c</i>-axis. We estimate around 5-10% of <i>I</i>4/<i>mcm</i>-type stacking in <i>P</i>4/<i>mbm</i> for RbCrF₃. In contrast, CsCrF₃ showcases a two-phase coexistence of <i>I</i>4/<i>mcm</i> and <i>P</i>4/<i>mbm</i> polymorphs and, as such, parallels to KCuF₃. We discuss and highlight the interplay between the impact of <i>A</i>-site cations and the Jahn-Teller effect acting on CrF₆ octahedra. Antiferromagnetic interactions dominate the paramagnetic regime, and RbCrF₃ and CsCrF₃ both have a Weiss temperature of -12 K, associated with Néel temperatures of 50 and 47 K, respectively. The effective paramagnetic moments of 4.65 and 4.68 μ_B for RbCrF₃ and CsCrF₃ are in good agreement with <i>S = 2</i> spin configuration.