(Oxo)(Fluoro)-Aluminates in KF-Al 2 O 3 System: Thermal Stability and Structural Correlation

Precise investigation of part of the phase diagram of KF-Al O system was performed in an experiment combining different techniques. Solidified mixtures of KF-Al O were studied by X-ray powder diffraction and high-field solid-state NMR spectroscopy over a wide range of compositions. To help with the interpretation of the NMR spectra of the solidified samples found as complex admixtures, we synthesized the following pure compounds: KAlO , K Al O , α-K AlF , KAlF , and K Al O F . These compounds were then characterized using various solid-state NMR techniques, including MQ-MAS and D-HMQC. NMR parameters of the pure compounds were finally determined using first-principles density functional theory calculations. The phase diagram of KF-Al O with the alumina content up to 30 mol % was determined by means of thermal analysis. Thermal analysis was also used for the description of the thermal stability of one synthesized compound, K Al O F .