Structural and Phase Transformations on the Surface of Superprotonic Crystals of Acid Salts of Potassium–Ammonium Sulfate

The results of comprehensive studies of structural and phase transformations in (K0.43(NH4)0.57)3H(SO4)2 superprotonic crystals under the influence of atmospheric moisture are presented. The real structure, composition, and thickness of the modified surface layers have been analyzed using scanning electron microscopy and X-ray microscopy. The local characteristics of nanostructures, formed on the freshly cleaved (001) crystal surface subjected to the electrostatic effect, have been investigated by conductive atomic force microscopy. A correlation has been established between the time changes in the structure, composition, and magnitude of the electrostatic potential of the crystal surface. The results are considered in the context of evaluation of the chemical stability of the samples and searching for the ways to optimize the compositions and functional properties of superprotonic compounds.