Ion mobility, phase transitions and conductivity in the fluorides (NH4)6LiZr3HfF23 and (NH4)6LiZrHf3F23

• Published in: Journal of solid state chemistry 2019-02, Vol.270, p.524-530
• Main Authors: Kavun, V.Ya, Antokhina, T.F., Savchenko, N.N., Polyantsev, M.M., Podgorbunskii, A.B.
• Format: Article
• Language: English
• Subjects: (NH4)6LiZr3HfF23; (NH4)6LiZrHf3F23; Conductivity; Ion mobility; NMR spectra; Phase transitions
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2018.12.024

Ion mobility, phase transitions, thermal and electrophysical properties in (NH4)6LiZr3HfF23 and (NH4)6LiZrHf3F23 fluorides have been studied by 1H, 19F NMR, X-ray diffraction, DSC and impedance spectroscopy. The types of ion motions in the fluoride and ammonium sublattices of the fluorides have been determined in temperature range of 150–450 K and their activation energy was estimated. The presence of order-disorder phase transition in these fluorides in the temperature range of 400–450 K with the formation of metastable high-temperature β–modifications in which diffusion of fluoride and ammonium ions is the dominant type of ionic motion is established. The values of conductivity at 453 K [(~ 9.4–6.6) × 10–3 S/cm] indicate that the studied fluorides belong to the class of superionic conductors. Temperature dependences of line width in 1H and 19F NMR spectra of studied fluorides. Inset shows the 19F NMR spectrum at 450 K after the PT. [Display omitted] •The ion mobility and conductivity in the fluorides (NH4)6LiZr4-xHfxF23 (x = 1, 3) were studied.•The main type of ion motion in studied fluorides above 370–400 K is diffusion of F– and NH4+ ions.•The phase transitions in these fluorides are connected with reaching of the superionic state.•The superionic states in studied fluorides are characterized by conductivity values of (6.7–9.4) × 10–3 S/cm at 453 K.