Crystal structure, hydrogen bonds and thermal transformations of superprotonic conductor Cs₆(SO₄)₃(H₃PO₄)₄

Abstract

Crystals of Cs6(SO4)3(H3PO4)4 belong to the family of alkali metal acid salts that show a high protonic conductivity at relatively low temperatures. Such properties make superprotonic crystals an excellent choice for the study of the influence of the hydrogen subsystem on the physicochemical properties and promising materials for energy-efficient technologies. Single crystals of Cs6(SO4)3(H3PO4)4 were studied by neutron diffraction methods, optical polarization microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Neutron diffraction studies made it possible to determine the positions of all the atoms with high accuracy, including the H atom on a hydrogen bond characterized by a single-minimum potential, to confirm the chemical composition of the Cs6(SO4)3(H3PO4)4 crystals and their cubic symmetry in low- and high-temperature phases, and to draw conclusions about the three-dimensional system of hydrogen bonds, which is fundamentally different in comparison with other superprotonic compounds. Based on the experimental data obtained, crystal transformations with temperature changes are reported, and the stability of the chemical composition is shown.

Features of Phase Formation in the CsOH–H2SO4–H3PO4–H2O System and the Growth of the Cs6(SO4)3(H3PO4)4 Crystals

“…Nevertheless, the Cs 6 (SO 4 ) 3 (H 3 PO 4 ) 4 crystal itself does not float in this solution. Given that the density of the fluoroplastic is ~2.2 g/cm 3 , and the X-ray density of the crystal according to [15] is 3.191 g/cm 3 , the density of the solution lies in the range of values 2.2-3.191 g/cm 3 .…”

“…At the same time, the crystal Cs 6 H(HSO 4 ) 3 (H 2 PO 4 ) 4 [14], formally not belonging to the CsHSO 4 -CsH 2 PO 4 system, was found. Subsequently, thanks to precision structural studies, it was found that a more correct structural formula for it would be Cs 6 (SO 4 ) 3 (H 3 PO 4 ) 4 [15].…”

“…Figure 5. The obtained powder X-ray diffraction pattern of the grown crystal Cs 6 (SO 4 ) 3 (H 3 PO 4 ) 4 .The indexing was carried out in accordance with the data[15].…”

Features of the crystal structure and surface of superprotonic conductor caesium hydrogen sulfate phosphate

“…This work is a continuation of our studies of superprotonic crystals M m H n (AO 4 ) (m+n)/2 •yH 2 O (M = K, Rb, Cs, NH 4 ; AO 4 = SO 4 , SeO 4 , HPO 4 , HAsO 4 ) by methods of structural analysis using X-ray, synchrotron radiation and neutrons. These studies also include complex caesium hydrogen sulfate phosphates Makarova, Selezneva et al, 2016;Mikheykin et al, 2017;Makarova et al, 2021;Komornikov et al, 2023), as well as the research of the real structure of the members of this family using electron and atomic force microscopy (Gainutdinov et al, 2021(Gainutdinov et al, , 2023Selezneva et al, 2023) in order to reveal regular relationships between their composition, structure and physical properties.…”