Conditions Extrêmes et Matériaux : Haute Température et Irradiation

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F.Šimko, A.Rakhmatullin, E.Veron, M.Allix, P.Florian, M.Kontrík, Z.Netriová, M.Korenko, V.Kavečanský, C.Bessada, 'Oxo‒ and (Oxo)(Fluoro)‒Aluminates in RbF‒Al2O3 System: Synthesis and Structural Characterization', Inorg. Chem. 57 13702-13712 (2018) doi:10.1021/acs.inorgchem.8b02275

Precise investigation of part of the phase diagram of RbF–Al2O3 system was carried out in an experiment combining thermal analysis, X-ray powder diffraction and high field solid state NMR spectroscopy. α-Rb3AlF6, RbAlO2, Rb2Al22O34 and new phase, Rb2Al2O3F2, were identified in the system. The structure of this new rubidium oxo-fluoro-aluminate was determined from X-ray diffraction data. It consists of individual layers of oxygen connected AlO3F tetrahedral groups with the fluorine atoms separating the layers. This type of structure exhibits a decent ionic conductivity at ambient temperature 1.74×10-6 The similar structural arrangement of O3Al−O−AlO3 and FO2Al–O–AlO2F tetrahedras of the conduction plans in Rb2Al22O34 and Rb2Al2O3F2 were confirmed by 27Al NMR measurements. The thermal analysis of RbF–Al2O3 system revealed that the system is not true binary, and it can be more defined as stable diagonal section of the quaternary system RbF–AlF3–Al2O3–Rb2O. From phase analysis of individual phase fields, the mutual metastable behavior of all founded phases can be considered. It was observed that fluoro- and oxo-aluminates existing side by side. Rb2Al2O3F2 is more stable under high-temperature conditions. Rubidium fluoro- and oxo-aluminates are metastable precursors of thermodynamically more stable structure of rubidium oxo-fluoro-aluminate.