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Pressure-dependent structural and chemical changes of the metal–organic framework (MOF) compound MIL-47­(V) have been investigated up to 3 GPa using different pore-penetrating liquids as pressure transmitting media (PTM). We find that at 0.3(1) GPa the terephthalic acid (TPA) template molecules located in the narrow channels of the as-synthesized MIL-47­(V) are selectively replaced by methanol molecules from a methanol–ethanol–water mixture and form a methanol inclusion complex. Further pressure increase leads to a gradual narrowing of the channels up to 1.9(1) GPa, where a second irreversible insertion of methanol molecules leads to more methanol molecules being inserted into the pores. After pressure release methanol molecules remain within the pores and can be removed only after heating to 400 °C. In contrast, when MIL-47­(V) is compressed in water, a reversible replacement of the TPA by H2O molecules takes place near 1 GPa. The observed structural and chemical changes observed in MIL-47­(V) demonstrate unique high pressure chemistry depending on the size and type of molecules present in the liquid PTM. This allows postsynthetic nonthermal pressure-induced removal and insertion of organic molecules in MOFs forming novel and stable phases at ambient conditions.

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In-situ high-pressure synchrotron X-ray powder diffraction studies up to 21 GPa of CVD-grown silicon 2D-nanosheets establish that the structural phase transitions depend on size and shape. For sizes between 9.3(7) nm and 15.2(8) nm we observe an irreversible phase transition sequence from I (cubic) → II (tetragonal) → V (hexagonal) during pressure increase and during decompression below 8 GPa the emergence of an X-ray amorphous phase. High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and atomic force microscopy (AFM) images of this X-ray amorphous phase reveal the formation of significant numbers of 1D nanowires with aspect ratios > 10, which are twinned and grow along the <111> direction. We discovered a reduction of dimensionality under pressure from a 2D morphology to a 1D wire in a material with a diamond structure. MD simulations indicate the reduction of thermal conductivity in such nanowires.

Superconductivity near room-temperature in the sulfur-hydrogen system arises from a sequence of reactions at high pressures, with x-ray diffraction experiments playing a central role in understanding these chemical-structural transformations and the corresponding S:H stoichiometry. Here we document x-ray irradiation acting as both a probe and as a driver of chemical reaction in this dense hydride system. We observe reaction between molecular hydrogen

Albite is one of the major constituents in the crust. We report here that albite, when subjected to hydrous cold subduction conditions, undergoes hitherto unknown breakdown into hydrated smectite, moganite, and corundum, above 2.9 GPa and 290 °C or about 90 km depth conditions, followed by subsequent breakdown of smectite into jadeite above 4.3 GPa and 435 °C or near 135 km depth. Upon the hydration into smectite, the fluid volume of the system decreases by ~14 %, whereas it increases by ~8 % upon its dehydration into jadeite. Both the hydration and dehydration depths are correlated to increases in seismicity by 93 % and 104 %, respectively, along the South Mariana trench over the past 5 years. Moreover, the formation of smectite is accompanied by the release of OH− species, which would explain the formation of moganite and expected alkalinity of the subducting fluid. Thus, we shed new insights into the mechanism of water transport and related geochemical and geophysical activities in the contemporary global subduction system.

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