Internal mobility, phase transitions, and ionic conductivity in (NH4)6KZr4F23 and (NH4)6KHf4F23

Abstract

The ion mobility, phase transitions (PTs), and conductivity in (NH 4 ) 6 KZr 4 F 23 (I) and (NH 4 ) 6 KHf 4 F 23 (II) have been studied by 1 H and 19 F NMR, DSC, and impedance spectroscopy. Types of ion motion in the fluorides and ammonium sublattices have been determined in the temperature range 150-480 K, and their activation energies have been evaluated. Compounds I and II undergo phase transitions in the temperature ranges 400-440 and 419-440 K, respectively, to form high temperature modifications. The high ionic conductivity in (NH 4 ) 6 KZr 4 F 23 and (NH 4 ) 6 KHf 4 F 23 (>10 -3 S/cm at 473 K) makes it possible to classify these compounds with superionic conductors.

Properties of New Superionic Compounds (NH₄)₆LiZr_4-nHf_nF₂₃ (n=1, 3)

“…Due to similarity of the IR spectra of the compounds in addition to the XRD data and taking into account the structure of the (NH 4 ) 6 LiZr 4 F 23 , it was suggested that compounds (NH 4 ) 6 LiZr 4-n Hf n F 23 have a chain structure which is analogous to the structure of (NH 4 ) 6 LiZr 4 F 23 . Taking into account the presence of phase transitions in the compounds (NH 4 ) 6 MZr(Hf) 4 F 23 (M = Li, Na, K, Rb) [11][12][13][14], it is quite ordinary that it will be attributed to (NH 4 ) 6 LiZr 4-n Hf n F 23 . This suggestion was confirmed by DSC data.…”