Journal of Applied Crystallography最新文献

Microstructural characterization of polycrystalline micropillars remains a significant challenge, particularly under time constraints such as those encountered during in situ or other time-sensitive experimental conditions, where appropriate data checks might assist in taking the right decision and have influence on the outcome of the experiment. In this study, we present a fast and efficient method for estimating local structural properties using scanning X-ray nanodiffraction-a technique widely employed in various dynamic and static micro- and nanoscale material investigations. The analysis targets the strongest diffraction peaks within the scattering pattern to extract essential information on grain orientation, size and lattice strain, while excluding weaker signals to streamline processing. As a case study, a γ-TiAl-based micropillar (Ti-46.5Al-5Nb), fabricated via Xe⁺ plasma focused-ion-beam milling, was analyzed before and after 10% uniaxial compression. The micropillar's grain size significantly exceeded the X-ray beam size (∼300 nm²), and its known crystallographic orientation enabled accurate tracking of structural evolution. A direct point-to-point comparison between the undeformed and compressed states revealed localized microstructural changes associated with plastic deformation. This approach provides a rapid and reliable means of assessing microstructural evolution and demonstrates high potential for in situ and operando investigations of small-scale materials.

For almost 30 years, the Zilman-Granek stretched exponential [Zilman & Granek (1996). Phys. Rev. Lett. 77, 4788-4791] has been used to obtain bending rigidities of membranes in lipid and surfactant vesicles from neutron spin echo data. However, with the advent of improved spectrometers that can easily measure Fourier times up to some 100 ns and even 1 µs, more subtle effects become visible in the data, which requires a refined theory. Recently, we published a framework for analysing such neutron spin echo data [Granek et al. (2024). Eur. Phys. J. E 47, 12]. Here, we apply this framework to different model membranes. The purpose of this paper is twofold. We intend to elucidate some often overlooked parameters, such as vesicle diffusion, size, lamellarity and membrane tension, that limit the quantitative interpretation of bending modulus values from NSE data. We also present some future opportunities to better understand the membrane dynamics and major sources of dissipation at the nanoscale uniquely probed with NSE.

Did you know that an X-ray diffraction pattern is not a spectrum? However, one in five scientific papers showing X-ray diffraction patterns refers to them as 'X-ray spectra'. Further, and in contrast to what is stated in many reference books, a triclinic substance could have a cubic-shaped cell. In crystal optics the terminology 'parallel Nicols' is almost always misused, and in the frame of polarizing microscope observations zoning is sometimes mistaken for twinning. In this paper, six recurring misconceptions in crystallography, including several related to mineral and crystal optics, are analyzed. Their prevalence is assessed through statistical data on their persistent appearances in peer-reviewed scientific literature. The objective of this study is to promote the correction of these misconceptions in academic communication and teaching. Furthermore, and according to some learning theories, the explanation of well established misconceptions could be used by teachers as an educational resource, offering powerful learning opportunities and contributing to talent development.

Anomalous X-ray diffraction has been applied for structure determination in both biological and inorganic systems. The ability to create elemental contrast by varying the X-ray energy around the absorption edge of a specific element makes it a viable tool to probe and locate specific elements within a crystal structure, providing valuable complementary information to standard X-ray diffraction. Considering the large amount of research on hybrid organic-inorganic perovskites for photovoltaic applications, it is surprising that anomalous diffraction experiments on these materials are rather under-explored. In recent years, hybrid lead halide perovskite materials have evolved as a promising material class for next-generation photovoltaic devices, as well as further applications. X-ray diffraction methods, including grazing-incidence and in situ techniques, are routinely implemented for structural investigations. This work presents anomalous diffraction studies on each component of hybrid metal halide perovskites, i.e. metal cation, halide anion and central cation, providing an overview of the opportunities and challenges associated with applying anomalous X-ray diffraction to hybrid metal halide perovskites. The results are consistent with model calculations on (pseudo-)cubic perovskite structures.

The bond valence sum (BVS) method has been extensively used to probe the ionic diffusion pathways within solids possessing high ionic conductivities, both anionic and cationic. For the former, the presence of lone-pair cations such as Tl⁺, Sn²⁺, Pb²⁺, Sb³⁺ and Bi³⁺ is known to enhance the anionic conductivity of solids by promoting disorder within the anion substructure and lowering the energy barriers between lattice sites. However, the BVS formalism assumes spherical ions and does not include the possibility of the more irregular co-ordination environments associated with electron lone pairs. We present here a simple modification of the BVS approach, which has been implemented in the form of a Python program that permits the preferred F^- diffusion pathways to be determined in fluoride ion conductors containing lone-pair cations. The method has been benchmarked by calculating energy barriers that broadly correlate with the F^- ionic conductivities of known compounds, and successfully reproduces the F^- distribution within the highly conducting compound β-PbSnF₄ determined by neutron powder diffraction and molecular dynamics (MD) methods. Using this new approach, fluoride compounds within the Inorganic Crystal Structure Database that contain at least one lone-pair cation have been screened and several new potential F^- ion conductors have been identified.

Crystallographic maps are typically computed as Fourier series using complex-valued structure factors, with a single set of coefficients applied across the entire region and associating a single resolution value with the whole map. In cryo-electron microscopy, however, experimental maps often have variable local resolution. As a consequence, applying the same procedure to compute model maps for comparison with the respective experimental ones becomes complicated. An alternative strategy involves representing model maps as sums of atomic images. They are oscillatory functions of the distance from the atomic center and depend on atomic displacement parameters and local resolution. To calculate such maps, we propose a stand-alone program which uses the shell-function approximation of atomic images, making them analytic functions of all their parameters including the local resolution associated with each atom.

We report a methodology based on wide-angle X-ray scattering (WAXS) to quantify the ordering between graphene oxide (GO) flakes in self-assembled films. By comparing WAXS signals of GO and graphite, we extract orientation distribution coefficients (S) from the GO 001 and (100) scattering features. To characterize the anisotropy in flake alignment, we define a ratio parameter (R) as the quotient of orientation distribution coefficients obtained under orthogonal orientations from the normal direction of the GO film with respect to the X-ray beam. This dimensionless ratio allows us to assess the degree of meso-structural anisotropy and condenses comparative orientation information into a single dimensionless metric, providing a new structural parameter for GO and related layered materials. In our measurements, R reached values of 0.11 for the GO 001 signal. These results demonstrate a metric for characterizing anisotropy in disordered 2D materials.

For specific setups, a diffraction pattern can contain gaps or missing information. For example, that is the case when several detectors are used simultaneously, but a particular angular range is not covered between each detector. In this article, a procedure for the reconstruction of the missing signal is proposed. It is based on a modified Papoulis-Gerchberg algorithm that considers features of the diffraction pattern without loss of generality. The mathematical basis of the algorithm is presented, and several cases, simulated and experimental, are used to test the performance and robustness of the proposed solution.

Samples used in electron microscopy are traditionally required to be stable under vacuum. However, many organic compounds with high vapor pressures readily sublime at room temperature, a process that is further accelerated under the high-vacuum conditions of an electron microscope. Here, we demonstrate for the first time the structure determination of vacuum-sensitive organic compounds in their solid state at room temperature using electron crystallography. Serial electron diffraction was employed to obtain sub-Å-resolution structures of anthracene and pyrene, two representative organic molecules which sublimate under the high-vacuum conditions of a transmission electron microscope. This was made possible by a simple sample preparation technique in which ultrathin crystals are encapsulated with a formvar layer to prevent sublimation under vacuum. By combining serial electron diffraction with formvar encapsulation, we demonstrate high-resolution structure determination of vacuum-sensitive samples at room temperature rather than cryogenic conditions. Moreover, by avoiding low-temperature phase transitions that can alter material properties, this method expands the accessible temperature range for studying the structural characteristics of vacuum-sensitive materials.

We have investigated the complete sequence of temperature-induced structural phase transitions in PrNiO₃ using high-angular-resolution synchrotron X-ray diffraction and symmetry-adapted distortion-mode analysis. By employing a high-purity sample synthesized under high pressure (3.5 GPa at 1073 K), we resolve the monoclinic (P2₁/n) → orthorhombic (Pbnm) → rhombohedral (R3c) evolution over an extended temperature range (10-900 K). Beyond confirming the role of oxygen stretching modes in the insulator-metal transition at ∼130 K, we show that these phonon modes also govern the high-temperature metallic-metallic transition at ∼750 K. This work provides a comprehensive mode-resolved picture of both insulator and metallic regimes in PrNiO₃ and highlights the central role of phonon-mediated processes in driving charge disproportionation and lattice symmetry breaking across all the crystalline phases.