Dynamically disordered hydrogen bonds in the hureaulite-type phosphatic oxyhydroxide Mn5[(PO4)2(PO3(OH))2](HOH)4

Abstract

We report the temperature evolution of hydrogen bond (HB) chains and rings in [Formula: see text] to reveal conduction pathways based on difference Fourier maps with neutron- and synchrotron x-ray diffraction data. Localized proton dynamics for the five distinct hydrogen sites were observed and identified in this study. Their temperature evaluation over ten orders of magnitude in time was followed by means of quasielastic neutron scattering, dielectric spectroscopy, and ab initio molecular dynamics. Two out of the five hydrogen sites are geometrically isolated and are not suitable for long-range proton conduction. Nevertheless, the detected dc conductivity points to long-range charge transport at elevated temperatures, which occurs most likely (1) over H4–H4 sites between semihelical HB chains (interchain-exchanges) and (2) by rotations of O1–H1 and site-exchanging H4–O10–O5 groups along each semihelical HB chain (intrachain-exchanges). The latter dynamics freeze into a proton-glass state at low temperatures. Rotational and site-exchanging motions of HOH and OH ligands seem to be facilitated by collective motions of framework polyhedra, which we detected by inelastic neutron scattering.

Angstrom-scale interface modification extensively tunes thermodynamic ordering of strongly correlated protons in ice

“…To unveil the emergent properties of such protonic nanomaterials, an in-situ observation technique to probe directly and noninvasively the proton configurations under the material growth processes and operating conditions is highly desirable. However, the experimental techniques commonly used to evaluate proton configurations in materials, such as neutron diffraction, typically require a macroscopic amount of the sample with dimensions on the order of millimeters 14,19 . Therefore, the detection sensitivity of neutron diffraction is still inadequate for application to interfacial systems with thicknesses on the angstrom to nanometre scale.…”