Conductivity, its anisotropy and changes as a manifestation of the features of the atomic and real structures of superprotonic [K_1–x (NH₄) _x ]₃H(SO₄)₂ crystals

Abstract

Single crystals of [K1–x (NH4) x ]3H(SO4)2 (x ≥ 0.57) grown in the K3H(SO4)2–(NH4)3H(SO4)2–H2O water–salt system are studied. The atomic structure including H atoms was determined at room temperature using X-ray structural analysis. [K1–x (NH4) x ]3H(SO4)2 (x ≥ 0.57) crystals have trigonal symmetry and disordered hydrogen-bond networks at ambient conditions similar to the high-temperature phases of K3H(SO4)2, (NH4)3H(SO4)2 and other superprotonic compounds M 3H(AO4)2. Impedance measurements performed on single crystals show high values of conductivity characteristic for superprotonic phases. Using the methods of impedance spectroscopy and atomic force microscopy, a significant anisotropy of the conductivity of crystals has been detected. It was also shown that there is a qualitative correlation of bulk and local conductivity measured for samples of the same composition and orientation at room temperature, which is due to the peculiarities of their crystal structure.

Regular relations of the composition, structure and properties of crystals of hydrogen-containing compounds

“…Подавляющее большинство структурных исследований проводится с использованием метода рентгеноструктурного анализа с применением рентгеновского или синхротронного излучения, что обусловлено его наибольшей эффективностью для установления атомной структуры кристаллов неорганических и органических соединений. Нужно отметить сложности при определении по рентгеновским данным атомов водорода, самого легкого элемента, что возможно, но требует более аккуратного подхода к проведению экспериментальной работы (Selezneva et al, 2023). Для определения легких атомов в присутствии более тяжелых, прежде всего атомов водорода, самым успешным считается нейтронографический метод.…”

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.…”

“…It was found that the superprotonic phase with a system of dynamically disordered hydrogen bonds can be formed at room temperature in the case of cation substitution, which is accompanied by an increase in the symmetry of their coordination environment (Selezneva et al, 2023). In the presence of crystallization water in crystals, the temperature increase will cause its diffusion from samples, and this process can also be accompanied by rearrangement of the hydrogen-bonding system into a dynamically disordered one with additional positions for protons, causing the appearance of proton conductivity.…”