Open Access

Show Abstract ▼

Abstract: Twinning-induced plasticity (TWIP) steels exhibit exceptional combinations of strength and ductility due to the activation of deformation twinning in the FCC austenite matrix. While the formation of deformation twins during monotonic deformation has been widely studied, the reversibility of twin-related defects during cyclic tensile loading and its influence on cyclic stability remain insufficiently understood. In this study, a high-Mn twinning-induced plasticity (TWIP) steel is investigated using in situ high-energy synchrotron X-ray diffraction during continuous cyclic tensile loading under two strain amplitudes over a wide temperature range (173–523 K). Time-resolved single-shot diffraction measurements enable quantitative tracking of stacking fault energy, twin fault probability, dislocation density and texture during deformation. The results reveal partially reversible evolution of faulted microstructures during cyclic tensile loading, indicating repeated activation of twinning and detwinning processes mediated by Shockley partial dislocations. Cyclic variations in stacking and twin fault probabilities demonstrate that twin boundary migration occurs dynamically during tensile cycling even in the absence of compressive load reversal. The degree of reversibility is strongly influenced by cyclic strain amplitude and temperature, which govern the relative contributions of dislocation slip, mechanical twinning, and limited FCC-to-HCP transformation. Enhanced twinning activity at lower temperature or higher cyclic strain leads to pronounced cyclic fluctuations in defect density and texture evolution. The present time-resolved diffraction approach provides new experimental insight into the micromechanical origins of cyclic stability in low stacking fault energy austenitic alloys and highlights the role of reversible twinning and detwinning processes in governing their deformation behaviour.

Open Access

Show Abstract ▼

Abstract: Co and Mn K-edge multiplets of bimetallic perovskite La2CoMnO6 nanoparticles (NP) and thin films are studied using high-resolution 1s2p resonant inelastic X-ray scattering (1s2p RIXS). Both the La2CoMnO6 NP and thin films exhibit Co2+ and Mn4+ valence states. A strong nonlocal peak is observed in the La2CoMnO6 NP, which becomes weaker in epitaxial La2CoMnO6 thin films grown on a SrTiO3 (0 0 1) substrate. Guided by charge-transfer multiplet calculations, the Co and Mn 1s to 3d quadrupole pre-edge X-ray absorption near-edge structure (XANES) and 1s2p RIXS spectra were calculated, showing good agreement with experimental observations. Using Density Functional Theory (DFT) + U simulations, the metal ions 1s to nonlocal 3d-4p dipole transitions are successfully reproduced. The nonlocal peak can be explained as dipole transitions to metal–metal charge-transfer interactions facilitated by the oxygen 2p state. This study underscores nonlocal hybridizations beyond the local 1s to 3d quadrupole transitions in K-edge X-ray absorption spectra.

Open Access

Show Abstract ▼

Abstract: The solvothermal synthesis of polycrystalline cubic CsMnF3 at 100 °C is reported, a phase previously prepared phase-pure only at 700 °C and 30 kbar. In situ powder X-ray diffraction, shows that cubic CsMnF3 transforms irreversibly to the 6H polymorph at ∼500 °C. The magnetic properties of cubic CsMnF3 are characterised by G-type antiferromagnetic ordering, as determined from powder neutron diffraction.

Show Abstract ▼

Abstract: Formamidinium lead iodide (FAPbI3), which has a narrower band gap close to the Shockley-Queisser limit, offers higher power conversion efficiency (PCE) than other perovskite compositions, surpassing 27% [1]–[3]. However, under external stressors like moisture in ambient air processing conditions, its high tolerance factor value causes phase instability because of the larger ion size of FA+ [4]–[6]. Additionally, a higher annealing temperature (>390 K) is needed to reach the cubic α-phase of FAPbI3, whereas lower temperatures result in the formation of a non-photoactive δ-phase [7]. In recent years, FAPbI3 perovskite ink has been extensively incorporated with volatile methylammonium chloride (MACl) as a transitional stabilizer [8]. This substance effectively provides FAPbI3 black phase without annealing by decreasing the formation energy. However, the advantageous effects of MACl as an α-phase FAPbI3 inducer and stabilizer at room temperature are neutralized under ambient conditions and in the presence of non-volatile coordinating DMSO, which is frequently used as a co-solvent with toxic DMF to regulate the crystallization process [9]. DMSO accelerates the α-to-δ phase transition in air by displacing MACl from the intermediate film through the formation of stronger bonds with PbI2. In this work, we use recently emerged Triethyl Phosphate (TEP) as a green solvent to dissolve FAPbI3 precursors and in-situ study its crystallization kinetics in the presence of MACl and excess PbI2 under ambient condition using transmission wide angle x-ray scattering (T-WAXS) [10] and steady-state photoluminescence (PL) techniques. Our results show that, unlike DMSO containing solvent systems, TEP with appropriate coordination ability allows for direct solvent extraction during anti-solvent quenching process avoiding intermediate phase formation. Furthermore, it has been found that the addition of excess PbI2 to the perovskite solution, along with MACl, not only regulates the pre-nucleation stage, leading to larger and more ordered crystals, as opposed to MACl alone as an additive, but also accelerates the formation of α-phase FAPbI3 at room temperature and stabilizes it under ambient condition during spin casting. This study paves the way for achieving high efficiency FAPbI3 solar cells using a non-toxic solvent system and under ambient conditions.

Show Abstract ▼

Abstract: Metal–organic frameworks (MOFs) are typically assembled from inflexible, 2D aromatic linker units to provide structural predictability, rigidity and prevent architectural collapse. Limiting the pool of structural units from which these materials are derived, however, inevitably restricts the diversity of architectures that can be realised. In this work, we have explored organic cages with 1,2,3-triazole struts as 3D linkers for Ag(I)-based MOFs. These linkers are unusual in two key facets. First, the cage structure is semi-rigid, providing both shape persistence and (limited) conformational freedom. Second, in contrast to the reticular design concepts of traditional MOFs, minor structural modifications at locations remote from the coordinating units were found to induce profound changes to the resultant MOF architectures, which included 2D honeycomb structures, 2D corrugated sheets and an interpenetrated 3D network. This is the first report of the incorporation of reduced symmetry cage linkers into metal–organic cage-to-framework structures, providing a blueprint for the introduction of low-symmetry and chiral intrinsic porosity into framework materials.