Ion mobility and phase transitions in heptafluorodiantimonates(III) Cs(1−x)(NH4)xSb2F7 and K0.4Rb0.6Sb2F7 according to NMR and DSC data

• The ion mobility and phase transitions in Cs(1−x)(NH4)xSb2F7 and K0.4Rb0.6Sb2F7 have been studied.
• The main type of ion motion in high-temperature phases is the diffusion of F− ions.
• The number of diffusing ammonium ions depends on the sample composition.
• Phase transitions in the samples studied are those into the superionic state.
• The ionic conductivity of the compounds studied is more than 10−3 S/cm at temperatures above 450 K.

Ion mobility and phase transitions in heptafluorodiantimonates(III) Cs1−x(NH4)xSb2F7 (x = 0.2; 0.6) and K0.4Rb0.6Sb2F7 were studied by the 19F, 1H NMR and DSC. The character of ionic motions in fluoride and ammonium sublattices with temperature variations was investigated. Types of ion motions and temperature ranges in which they are observed were determined. It was found that the predominant form of ionic motions in high-temperature modifications is a diffusion of fluorine atoms, whereas the number of diffusing ammonium ions depends on the sample composition. The observed phase transitions in heptafluorodiantimonates(III) of cesium–ammonium and potassium–rubidium with a formation of high-temperature modifications are transitions into a superionic state (σ > 10−3 S/cm above 450 K).

Phase transitions in Cs1−x(NH4)xSb2F7 (x = 0.2; 0.6) and K0.4Rb0.6Sb2F7 in the temperature range 150–450 K with the formation of modifications, in which the dominating type of ionic mobility becomes diffusion of fluorine ions and, partially, ammonium ions, are those into the superionic state (conductivity σ above 10−3 S/cm).Figure optionsDownload as PowerPoint slide