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Precise investigation of part of the phase diagram of KF-AlO system was performed in an experiment combining different techniques. Solidified mixtures of KF-AlO 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, KAlO, α-KAlF, KAlF, and KAlOF. 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-AlO 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, KAlOF.

The diffusion coefficient of Cr(III) determined by chronopotentiometry in the molten system NaF-AlF 3 -CrF 3 was found to be D(Cr(III)) = (5.28 ± 0.14) × 10 −5 cm 2 s −1 . The molar ratio CR = n(NaF)/n(AlF 3 ) was 1.4, which allowed us to perform measurements at 900 • C. When oxygen anions were present in the melt, chromium was deposited simultaneously with aluminium at the cathode, and the apparent diffusion coefficient related to Cr(III) was too high by two orders of magnitude. This may be explained by the formation of oxofluoro complexes of chromium and aluminium. The solubility of Cr 2 O 3 was studied in the above-mentioned melt at 900 • C by two methods: chemical analysis of solidified samples and by chronopotentiometry. It was found that saturation was achieved after several hours, and the concentration of chromium was (177 ± 6) ppm, corresponding to (258 ± 9) ppm Cr 2 O 3 .

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The electrical conductivity of low-temperature electrolytes based on Na3AlF6 was measured by means of a tube-type cell. AC-techniques with a sine wave signal in the high frequency range were applied. Basic binary melts NaF-AlF3 were studied at different molar cryolite ratios MR = (2.0–1.2) in the temperature range from the temperature of primary crystallization to 100°C overheat. The influence of the additions of 2 wt% of Al2O3, 5 wt% of CaF2 or 2 wt% of MgF2 was investigated at the same conditions, as well. The temperature and concentration dependencies of the conductivity in the studied systems were determined.

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