Journal of Applied Crystallography最新文献

Luminescence thermometry based on Ce³⁺-doped materials is limited by the lack of well separated emission bands and the nanosecond timescale of the 4f–5d transition, which complicate conventional temperature-readout methods. In this work, we demonstrate the application of principal component analysis (PCA) to enhance the temperature sensitivity of BaF₂:Ce³⁺ single crystals. A crystal was grown by the vertical Bridgman method and characterized structurally and spectroscopically. Temperature-dependent photoluminescence spectra were recorded in the 300–550 K range under 270 nm LED excitation. PCA was applied to the emission spectra, enabling dimensionality reduction and extraction of a principal component (PC₁) that exhibits a strong monotonic dependence on temperature. This PCA-based method achieves an average temperature resolution of ∼1 K, overcoming the limitations of traditional luminescence intensity ratio techniques for Ce³⁺ systems. These results highlight the potential of PCA for practical high-precision luminescence thermometry using Ce³⁺-doped materials.

X-ray stress analysis requires accurate X-ray elastic constants (XECs). One of the challenges for XEC calculation is that the modelling approach, preferred orientation and, to a lesser extent, the free surface affect the result. In this work, we investigate these factors. The surface effect is calculated under the assumption that within a surface layer the Poisson action along the normal direction caused by in-plane stresses must not be impeded by grain–matrix interaction in the normal direction due to the free surface. The model is evaluated for the pure surface effect for zero penetration and for a layer thickness equal to the grain size; the latter is calculated as the attenuation-weighted depth average of the surface grain layer and the bulk. Further comparisons are made with other XEC models and with measured XECs for different lattice planes (hkl), different X-ray wavelengths and varying penetration depths. The effect of preferred orientation is studied through variations of the grain orientation distribution function (ODF). It was found that the pure-surface-effect model performed best. ODF variations can significantly affect the XECs of individual (hkl), while the effect on the (hkl) average appears small.

Resolution smearing is a critical challenge in the quantitative analysis of two-dimensional small-angle neutron scattering (SANS) data, particularly in studies of soft-matter flow and deformation using SANS. We present a central moment expansion technique to address smearing in anisotropic scattering spectra, offering a model-free desmearing methodology. By accounting for directional variations in resolution smearing and enhancing computational efficiency, this approach reconstructs desmeared intensity distributions from smeared experimental data. Computational benchmarks using interacting hard-sphere fluids and Gaussian chain models validate the accuracy of the method, while simulated noise analyses confirm its robustness under experimental conditions. Experimental validation using rheological SANS data from shear-induced micellar structures demonstrates the practicality and effectiveness of the proposed algorithm. The desmearing technique provides a powerful tool for advancing the quantitative analysis of anisotropic scattering patterns, enabling precise insights into the interplay between material microstructure and macroscopic flow behavior.

High-temperature powder X-ray diffraction is currently the most widely used method to trace changes in unit-cell dimensions and estimate the thermal behavior of crystal structures. Single-crystal X-ray diffraction (SCXRD) is used much less frequently for these purposes due to the technical difficulties associated with experiments. However, modern diffraction equipment allows researchers to make use of the undeniable advantages of direct determination of subtle crystal-chemical parameters, which are responsible for structural dynamics and transformations with temperature variations. The benefits of high-temperature SCXRD studies as well as the challenges that this technique brings are discussed in detail using a synthetic analog of the uranyl sulfate mineral shumwayite, [(UO₂)(SO₄)(H₂O)₂]₂·H₂O, as an example. In addition, the details of crystal lattice dynamics are discussed, including unit-cell parameters, bond lengths and bond-valence changes with temperature. Observed anomalies in bond-length and bond-valence behavior are discussed in the context of rigid-body motion and the independent atom model (IAM). To further illustrate the influence of the chosen refinement method, the structure of quartz was investigated using high-temperature SCXRD and refined using both IAM and Hirshfeld atom refinement.