No abstract

The majority of research into metal-organic frameworks (MOFs) focuses on their crystalline nature. Recent research has revealed solid-liquid transitions within the family, which we use here to create a class of functional, stable and porous composite materials. Described herein is the design, synthesis, and characterisation of MOF crystal-glass composites, formed by dispersing crystalline MOFs within a MOF-glass matrix. The coordinative bonding and chemical structure of a MIL-53 crystalline phase are preserved within the ZIF-62 glass matrix. Whilst separated phases, the interfacial interactions between the closely contacted microdomains improve the mechanical properties of the composite glass. More significantly, the high temperature open pore phase of MIL-53, which spontaneously transforms to a narrow pore upon cooling in the presence of water, is stabilised at room temperature in the crystal-glass composite. This leads to a significant improvement of CO 2 adsorption capacity.

Stable but not quite cubic The black, photoactive phase of formamidinium (FA) perovskites, which is usually stabilized by cation alloying to avoid the formation of inactive hexagonal phases, is assumed to be cubic. High-resolution microscopy studies by Doherty et al . using nanoscale probes revealed that these FA-rich phases are not cubic but rather undergo slight tilting (by two degrees) of the octahedra. Black phases can have localized regions of hexagonal phases that nucleate degradation. Surface-bound ethylenediaminetetraacetic acid stabilized the tilted phase of pure FA lead triiodide against environmental degradation. —PDS

Understanding the nanoscopic chemical and structural changes that drive instabilities in emerging energy materials is essential for mitigating device degradation. The power conversion efficiency of halide perovskite photovoltaic devices has reached 25.7% in single junction and 29.8% in tandem perovskite/silicon cells 1,2 , yet retaining such performance under continuous operation has remained elusive 3 . Here, we develop a multimodal microscopy toolkit to reveal that in leading formamidinium-rich perovskite absorbers, nanoscale phase impurities including hexagonal polytype and lead iodide inclusions are not only traps for photo-excited carriers which themselves reduce performance 4,5 , but via the same trapping process are sites at which photochemical

Metal fluorides, promising lithium-ion battery cathode materials, have been classified as conversion materials, due to the reconstructive phase transitions widely presumed to occur upon lithiation. We challenge this view by studying FeF3 using X-ray total scattering and electron diffraction techniques that measure structure over multiple length-scales coupled with DFT calculations, and by revisiting prior experimental studies of FeF2 and CuF2. Metal fluoride lithiation is instead dominated by diffusioncontrolled displacement mechanisms, a clear topological relationship between the metal fluoride Fsublattices and that of LiF being established. Initial lithiation of FeF3 forms FeF2 on the particle's surface, along with a cation-and stacking-disordered phase, A-LixFeyF3 -structurally related to α-/β-LiMn 2+ Fe 3+ F6, which topotactically transforms to Band then C-LixFeyF3, before forming LiF and Fe. Lithiation of FeF2 and CuF2 results in a buffer phase between FeF2/CuF2 and LiF. The resulting principles will aid future developments of a wider range of isomorphic metal fluorides.