Ion mobility, phase transitions, and conductivity of crystal phases in KF-CsF-SbF3-H2O system according to data of NMR and impedance spectroscopy

Ion mobility and phase transitions in heptafluorodiantimonates(III) Cs (1−x) (NH 4 ) x Sb 2 F 7 and K 0.4 Rb 0.6 Sb 2 F 7 according to NMR and DSC data

“…According to the DSC and NMR data, in the temperature range of 415-460 K the compounds CsSb 2 F 7 , NH 4 Sb 2 F 7 , Cs 0.8 (NH 4 ) 0.2 Sb 2 F 7 , Cs 0.4 (NH 4 ) 0.6 Sb 2 F 7 , and K 0.4 Rb 0.6 Sb 2 F 7 undergo phase transitions (Table 1) resulting in a formation of high-temperature phases with highly mobile fluoride ions. The preliminary results of ionic conductivity (s > 10 À4 S/cm) show, that the PTs are phase transitions into a superionic state that is characteristic for many fluoroantimonates(III) with alkali metals and ammonium cations [6][7][8][9]14,15]. The probability of a transition of ammonium ions from isotropic reorientations to diffusion and the number of highly mobile NH 4 + ions depend on the sample composition.…”

“…local motions (reorientations of fluorine-containing antimony groups) ! translational diffusion, which is typical for many fluoroantimonates(III) and fluorozirconates with homoand heteroatomic cations [7,9,14,15,20,28,29,31]. The dynamic state of the fluoride sublattice in the compounds Cs 1Àx (NH 4 ) x Sb 2 F 7 is determined by the number of ammonium cations introduced into the cesium subsystem.…”

“…The transformation time depends on the compound composition, the temperature and time of the sample heating. Taking into account a diffusion in the compounds I-III, the electro-physical data for crystalline phases of the compositions K 1Àx (NH 4 ) x SbF 4 [14], K 1Àx Cs x SbF 4 [15], and the preliminary results on ionic conductivity (s = 8 Â 10 À4 S/cm for K 0.4 Rb 0.6 Sb 2 F 7 at 433 K), it is possible to expect a high ionic conductivity in the studied samples in the temperature range of 450-500 K (10 À3 -10 À2 S/cm). If this assumption is confirmed, then compounds in the systems M 1Àx M 0…”

“…The ion mobility was studied in the compounds K (1Àx) (NH 4 ) x SbF 4 [14], K (1Àx) Cs x SbF 4 [15], and Cs (1Àx) K x Sb 2 F 7 [16]. There is no published data on the character of dynamic processes in the crystalline phases Cs 1Àx (NH 4 ) x Sb 2 F 7 (x = 0.2, 0.6) and K 0.4 Rb 0.6 Sb 2 F 7 .…”