Crystal Structures of Three Polymorphs of Cs₃ScF₆ by Means of Solid-State NMR, X‑Ray, and NeutronDiffraction

Three polymorphs were found to exist for Cs₃ScF₆ in the room temperature range of up to 280 °C. Two phase transitions were identified by differential scanning calorimetry (DSC) analyses at 92 and 196 °C upon heating. In situ high-temperature solid-state NMR, synchrotron and laboratory X-ray diffraction, and neutron powder diffraction were used for structural characterization. The crystal structure of the high-temperature (γ) phase adopts the cubic <i>Fm</i>3̅<i>m</i> (<i>Z</i> = 4) space group with <i>a</i> = 9.6048(7) Å at 250 °C. The other two polymorphs, α and β, have tetragonal symmetry with space groups <i>I</i>4₁/<i>a</i> (Z= 80) and <i>I</i>4/<i>m</i> (Z= 10), and lattice parameters are <i>a</i> = 21.15222(6) Å, <i>c</i> = 38.21648(8) Å and <i>a</i> = 15.0401(2) Å, <i>c</i> = 9.6341(2) Å at RT and 150 °C, respectively.