Ion mobility, conductivity, structure, and phase transitions in K0.7M0.3SbF4 compounds with M=Rb, NH4

Abstract

Ion mobility, phase transitions, structure, and conductivity in the K0.7M0.3SbF4 (M=Rb, NH4) compounds were studied by NMR spectroscopy, DSC, X-ray, and conductivity measurements. The predominant form in the ion motions resulting from the phase transition of high modification was diffusion of fluoride and ammonium ions above 450K. The high–temperature phases of K0.7M0.3SbF4 (M=Rb, NH4) are superionic, while their conductivity attains the values of ~10−2–10−4S/cm at 450–500K. The structures of α– and β–modifications of the K0.7Rb0.3SbF4 are monoclinic (space group P21/m). The main structural units in them are statistically substituting each other K+ and Rb+ cations and complex [SbF4]−∞1 anions linked into zigzag-like chains by bridge fluorine atoms. The nearest surrounding of each antimony atom contains five fluorine atoms, so that the antimony coordination polyhedron can be described, taking into account the lone electron pair, as a distorted SbF5E octahedron (ψ-octahedron).