Ionic mobility and phase transitions in heptafluorodiantimonates MSb2F7 and Cs(1−x)M x ′Sb2F7 (M′ = K, NH4) according to NMR and DSC data

Abstract

Ionic mobility and phase transitions in heptafluorodiantimonates with homo- and heteroatomic cations in the systems MSb2F7 (M = K, Cs, NH4) and CsM’Sb2F7 (M’ = K, NH4) have been studied using the 19F, 1H NMR and DSC methods. Analysis of the 19F and 1H NMR spectra made it possible to reveal the nature of ion motions in the fluoride and proton sublattices upon temperature variation and to determine the types and temperature ranges of such motions. It was found that diffusion of fluorine ions becomes the dominant form of ion motions in the high-temperature modifications, the amount of diffusing ammonium ions depending on the composition of a sample. The observed phase transitions in cesium-potassium and cesium-ammonium fluoroantimonates(III) leading to the formation of high-temperature modifications are the transitions to superionic state. According to preliminary results of electrophysical studies, hightemperature phases Cs1−x(NH4)xSb2F7 (0.05 ≤ x ≤ 0.6) are superionic, their conductivity reaching −10−3-10−4 S/cm at 463–483 K.