Applying neutron powder diffraction, four unique hydrogen positions were determined in a rockbridgeite-type compound, Fe 2+ Fe 3+ 3.2 (Mn 2+ , Zn) 0.8 (PO 4 ) 3 (OH) 4.2 (HOH) 0.8 . Its honeycomb-like H-bond network running without interruption along the crystallographic a axis resembles those in alkali sulphatic and arsenatic oxyhydroxides. They provide the so-called dynamically disordered H-bond network over which protons are superconducting in a vehicle mechanism. This is indicated by dramatic increases of dielectric constant and loss factor at room temperature. The relevance of static and dynamic disorder of OH and HOH groups are explained in terms of a high number of structural defects at octahedral chains alternatingly half-occupied by Fe 3+ cations. The structure is built up by unusual octahedral doublet, triplet, and quartet clusters of aliovalent 3d transition metal cations, predicting complicate magnetic ordering and interaction. The ferrimagnetic structure below the Curie temperature T C = 81-83 K could be determined from the structure analysis with neutron diffraction data at 25 K.
The low temperature antiferromagnetic (AF) phase of MnWO (the so-called AF1 phase) exhibits different spin-canting configurations at two Mn sublattices of the (3 + 1)-dimensional magnetic structure. The suggested superspace group [Formula: see text] is a significant consequence of the polar space group [Formula: see text]2 true for the nuclear structure of MnWO. Density functional theory calculations showed that its ground state prefers this two spin-canting system. The structural difference between two independent atomic sites for Mn (Mn , Mn ) is too small to allow microscopically detectable electric polarisation. However, this hidden intrinsic polar character allows AF1 two commensurately modulated spin-canting textures. This is considered as the prerequisite onset of the improper ferroelectricity enhanced by the helical spin order in the multiferroic phase AF2 of MnWO.
Uranium-molybdenum (UMo) alloy embedded in an Al matrix (UMo/Al) has been considered as a promising candidate for fuel conversion of research reactors. A modified system with a diffusion barrier, UMo/X/Al trilayer (X = Ti, Zr, Nb, and Mo), has been investigated in order to suppress interdiffusion between UMo and the Al matrix. The trilayer was tested by swift heavy ion irradiation, followed by Rutherford backscattering spectroscopy (RBS) and Xray microdiffraction (µ-XRD). Atomic mixing at the interfaces was resolved by RBS, indicating that Ti interacts strongly with UMo while Zr does with Al. µ-XRD revealed the formation of intermetallic AlX compounds which can detain further atomic mixing. However, Ti and Zr as diffusion barrier can be controversial because their presence might lead to γ-UMo decomposition. This study presents the effectiveness of diffusion barriers and the irradiationinduced phase impacting on the properties of the UMo/X/Al trilayer.
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.
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