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Abstract: Despite remaining enigmatic, strong hydrogen bonding provides an advanced design handle for tailoring the properties of functional materials. Here, 3R–(H/D)RhO2 delafossites (prepared by ion exchange of Na+ from NaRhO2) contain H/D in linear coordination with O, linking RhIIIO2 layers. Bragg and real-space X-ray and neutron scattering analysis, vibrational and solid-state NMR spectroscopy, and density functional theory (DFT)–based electronic structure calculations have been employed to understand the nature of the hydrogen bonding. Despite short distances between H/D and the two O to which they are bonded, a clear double-minimum corresponding to a shorter and longer (H/D)–O distance is established. The triangular lattices formed by H/D appear to display ice-like disorder, corroborated by low-temperature heat capacity measurements.

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Abstract: Layered crystal structures are commonly found across organic and inorganic material systems. When in-plane atomic arrangement remains (nearly) identical, a stacking variation of these layers may result in twinning, planar disorder, or polytypes, a form of polymorphism derived from altering stacking sequences. In this work, we use multi-dimensional electron diffraction (ED) modalities to explore the microstructure of xanthine, an archetypal purine base with a layered crystal structure. Firstly, we identify and characterise the twin operator relating domains of Form I xanthine. We then solve the structure of a new xanthine polymorph, revealing that it is a polytype of Form I. Finally, interfaces between twin and polytype domains are visualised, whilst streaking in the diffraction patterns reveals the presence of planar disorder. Given these observations in the xanthine system, this work suggests that disorder on the nanoscale may be a commonly occurring phenomenon in layered organic molecular crystals.

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Abstract: Theoretical calculations of materials have in recent years shown promise in facilitating the analysis of convoluted experimental data. This is particularly invaluable in complex systems or for materials subject to certain environmental conditions, such as those exposed to X-ray radiation during routine characterisation. Despite the clear benefit in this use case to shed further light on intermolecular damage processes, the use of theory to study radiation damage of samples is still not commonplace, with very few studies in existing literature. In this paper, we demonstrate the potential of density functional theory for modelling the electronic structure of two industrially important organometallic systems of the formula [M(COD)Cl]2 where M=Ir/Rh and COD=1,5-cyclooctadiene, which are subject to X-ray irradiation via X-ray Diffraction and X-ray Photoelectron Spectroscopy. Our approach allows calculated spectra to be compared directly to experimental data, in this case, the X-ray photoelectron valence band spectra, enabling the valuable correlation of individual atomic states to the electronic structure.

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Abstract: Two-dimensional layered perovskite oxides have emerged as promising photocatalysts for solar-driven hydrogen evolution. Although doping has been widely employed to enhance photocatalytic performance, its role in modulating the electronic structure and the local chemical environment of these materials remains poorly understood. Here in this study, we investigate the codoping of Rh and La into exfoliated nanosheets of the Dion–Jacobson perovskite KCa2Nb3O10 to enhance photocatalytic hydrogen evolution reaction (HER) activity. A substantial increase in H2 evolution rate, from 12.3 to 69.0 μmol h–1, was achieved at an optimal doping level of 0.2 wt % Rh and 1.3 wt % La. Comprehensive structural and spectroscopic analyses, including synchrotron techniques and high-resolution microscopy, revealed that Rh3+ substitutes Nb5+ to introduce shallow 4d acceptor states that mediate charge separation, while La3+ substitutes Ca2+, compensates for aliovalent charge imbalance, and modulates local lattice distortions and oxygen vacancy formation. This codoping strategy enhances charge carrier lifetime and separation efficiency through a trap-mediated mechanism. The observed volcano-shaped activity trend highlights a narrow compositional window, where electronic and structural factors are optimally balanced. These findings establish a mechanistic foundation for defect engineering in layered perovskites and offer a pathway for the rational design of photocatalysts.

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Abstract: The paper presents the study of phase and structural behavior of pseudoternary compound (Ga1-x-yInxAly)2O3 with focus on the compositional cross-section where the x/y ratio is a fixed at 0.31/0.69. This specific ratio ensures that the average cation radius, equal to that of Ga3+ ions, remains unchanged. Through the combination of experimental XRD studies and DFT calculations, the stability region of the monoclinic phase within the Ga2O3–Al2O3–In2O3 ternary system was established. Detailed analysis of the crystal lattice parameters and unit cell volume of the monoclinic structure was carried out across a wide range of compositions. An empirical relationship was derived linking the monoclinic lattice parameters to the average ionic radius of the cations (Ga3+, Al3+, In3+) enabling prediction of lattice parameters in monoclinic (Ga1-x-yInxAly)2O3 solely from chemical composition. The experimental crystal structure studies and the electronic structure calculations suggest that in the monoclinic (Ga1-x-yInxAly)2O3 structure the tetrahedral positions of Ga1 atoms are preferentially occupied by Ga3+ and Al3+ cations, while the octahedral Ga2 sites accommodate a mixture of Ga3+, Al3+ and In3+ cations. Additionally, the presence of unidentified phase(s) was confirmed in the central region of the Ga2O3–Al2O3–In2O3 triangle. Comparison of the calculated optical absorption spectra and the Tauc-plots derived from the diffuse reflectance spectra indicate that the monoclinic (Ga1−x−yInxAly)2O3 compounds have a direct band gap.