arXiv subjects

Nicholas A. Strange

Publications and source records attributed to Nicholas A. Strange.

3 recordsLinked to original sources

arXiv2026

Automating the analysis of micron-scale synchrotron diffraction data on inhomogeneous polycrystalline samples: a solid oxide electrolysis cell case study

A novel approach to post mortem characterisation of electrochemical and photovoltaic devices is spatially-resolved diffraction using a hyper-focused, micron-width x-ray beam to examine the distribution of degradation products and strain, a technique called $\mu$-XRD. Aside from the experimental difficulties associated with beam focusing and sample preparation, which are themselves non-trivial, the analysis of resulting data is complex and challenging, with full Rietveld analysis rarely attempted in literature. The difficulty lies in the size of the data, which may consist of hundreds or even thousands of diffraction patterns with very different crystallographic phase compositions depending on position within the device, and the difficulty in fitting the data due to the presence of many phases at the same position, including possible degradation products which may be difficult to index and assign to known phases. In this paper, we present a fully-automated open access Python routine for performing phase identification and Rietveld analysis on 2D datasets of diffraction pattern taken at micron-scale positions, measured over the cross-section of a chemically inhomogeneous device with polycrystalline phases. Solid oxide electrolyser cells are a promising technology for green hydrogen production which can utilise waste heat to split water at higher efficiencies than low-temperature electrolysis techniques such as polymer electrolyte membranes, but exhibit many degradation modes due to the high operating temperatures. We present a case study using our analysis protocol on an SOEC fragment encompassing the air electrode, cation diffusion barrier, electrolyte, and fuel electrode. With modification, this protocol could be applied to other devices such as all-solid-state batteries, wet-electrolyte battery electrodes, solid oxide fuel cells, photovoltaic devices, and metal-oxide pseudocapacitors.

cond-mat.mtrl-sci↗

arXiv2026

Composition-dependent Thin-film Synthesis of Layered Ternary Iron Nitrides FeMN2 (M = W, Mo)

Ternary transition-metal nitrides with layered crystal structures host anisotropic bonding and reduced dimensionality that may enable unconventional electronic and magnetic behavior. Yet, synthesis of such nitride thin films remains challenging because reactive sputtering often favors metastable rocksalt-derived structures. We report the composition-dependent synthesis, structure, and properties of layered FeMN2 (M = W, Mo) thin films with triangular Fe sublattices, prepared by reactive sputtering and post-deposition NH3 annealing. Using synchrotron grazing-incidence wide-angle X-ray scattering (GIWAXS) and X-ray absorption spectroscopy (XAS), we investigate the evolution of phase formation, crystallographic texture, and local Fe coordination across composition. Both layered phase form over broad composition ranges. FeWN2 maintains high phase purity across compositions, consistent with cation substitution, whereas FeMoN2 only exhibits good phase purity at Fe-poor compositions. Azimuthal GIWAXS analysis shows that Fe-rich films in both systems exhibit out-of-plane fiber texture, which progressively evolves toward predominantly in-plane orientation near stoichiometry in FeWN2, while FeMoN2 develops a more randomly oriented polycrystalline microstructure. Electrical measurements reveal relatively low and composition-insensitive resistivity in FeWN2 (~1 m{\Omega}.cm), whereas FeMoN2 exhibits a pronounced resistivity maximum near nominal stoichiometry. Preliminary room-temperature magnetization measurements on FeWN2 further reveal weak ferromagnetic-like behavior in Fe-poor films, while stoichiometric compositions remain predominantly paramagnetic. These results demonstrate fundamentally different structural accommodation mechanisms in FeWN2 and FeMoN2, and highlight the strong coupling between composition, microstructure, and electronic/magnetic properties in layered nitride thin films.

cond-mat.mtrl-sci↗

arXiv2025

Orientational Disorder of NH$_3$ in Hexammine Magnesium Borohydride

Hexammine magnesium borohydride, Mg(NH$_3$)$_6$(BH$_4$)$_2$, consists of adducted NH$_3$ molecules locked in a matrix of Mg cations and borohydride anions. It is a candidate material for hydrogen storage, with 16.8wt\% hydrogen stored in both the NH$_3$ and borohydride anions. It also may be of interest as a Mg$^{2+}$ conducting electrolyte in solid state batteries. Its crystal structure has, until now, eluded a proper structural solution due to ambiguity regarding the NH$_3$ position and behaviour. In this work, we show using synchrotron X-ray diffraction that the room-temperature structure can be solved only with a model assuming orientational disorder of ammonia molecules within the crystal structure. Cooling the sample to 120\,K yields additional Bragg peaks, which can only be solved with a unit cell expansion consistent with a freezing of the orientational freedom of ammonia molecules. Using this insight from the structure solution, we perform a full assignment of the vibrational modes in the room-temperature IR spectrum.

cond-mat.mtrl-sci↗