Conditions Extrêmes et Matériaux : Haute Température et Irradiation
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2020

ACL
doi

M.Boča, M.Molokeev, A.Rakhmatullin, Z.Netriová, 'The structure of the metastable K18Ta5Zr5F63 phase', New J. Chem. 44 9264-9270 (2020) doi:10.1039/d0nj02428g

A metastable phase K18Ta5Zr5F63 was prepared by molten salt synthesis of K2TaF7 and K2ZrF6 in a sealed Pt crucible. This is the first example of a structure of a fluoride complex compound containing both tantalum and zirconium as central atoms. The independent part of the unit cell contains two Ta/Zr sites and one pure Zr site. The Ta1/Zr1 ion is coordinated by seven F ions forming one capped trigonal prism. The Ta2/Zr2 ion is coordinated by six F ions forming a trigonal prism, and this polyhedron is fully ordered. The Zr3 ion is coordinated by six F ions, which are disordered over two positions. All (Zr/Ta)Fn (n=6,7) polyhedra are isolated from each other, although the ZrF6 units have shared faces, forming an infinite channel along the c-axis. 19F MAS NMR experiments agree with the proposed structural model, identifying all five central non-equivalent polyhedra. The K18Ta5Zr5F63 phase decomposes within several months to its initial components; this can be monitored by NMR, DSC and XRD experiments. Moreover, accelerated decomposition can be achieved by thermal treatment, resulting in the formation of a K3ZrF7 phase.