Polymorphs of Rb₃ScF₆: X-ray and Neutron Diffraction, Solid-State NMR, and Density Functional Theory Calculations...

Area of Science:

• Solid-state chemistry
• Crystallography
• Materials science

Background:

• Rubidium hexafluoroscandate (Rb3ScF6) is a compound with potential applications in materials science.
• Understanding its polymorphic behavior is crucial for controlling its properties.

Purpose of the Study:

• To elucidate the crystal structures of three polymorphs of Rb3ScF6.
• To characterize the phase transitions and structural details of these polymorphs.

Main Methods:

• Synchrotron and laboratory X-ray powder diffraction
• Neutron powder diffraction
• Electron diffraction
• Multinuclear high-field solid-state NMR spectroscopy
• Density functional theory calculations

Main Results:

• Three polymorphs (α, β, γ) of Rb3ScF6 were identified with distinct crystal structures (tetragonal and cubic) and lattice parameters.
• Phase transitions were observed at 141 °C and 201 °C.
• The structures were found to be isostructural with corresponding forms of potassium cryolite.
• Dynamic rotations of ScF6 octahedra in the β polymorph were detailed.

Conclusions:

• The study provides a comprehensive structural characterization of Rb3ScF6 polymorphs.
• The findings contribute to the understanding of phase behavior in fluoride compounds.
• Detailed structural insights pave the way for potential applications.