This Highlight explores the progress and perspective in studies of metal–organic frameworks (MOFs), a new class of nanoporous materials, particularly suited for storage and separation applications related to energy utilization and environmental remediation. Since the discovery of the first MOF compound, hundreds of different MOFs have been developed and reported. MOFs are generally synthesized by self-assembly of metal ions/clusters as coordination centers and organic ligands as linkers. They possess intriguing chemical and physical properties and are structurally tunable, thermally stable and mechanically sound. MOFs are increasingly proving to be a superior class of materials for state-of-the-art applications in crystal engineering, chemistry, and materials science. In this Highlight, we present general routes for MOFs synthesis, discuss reticular design of their pore structures, and show some of their remarkable applications, especially in the areas of storage and separation.
Constitutive laws and crystal plasticity in diamond deformation have been the subjects of substantial interest since synthetic diamond was made in 1950's. To date, however, little is known quantitatively regarding its brittle-ductile properties and yield strength at high temperatures. Here we report, for the first time, the strain-stress constitutive relations and experimental demonstration of deformation mechanisms under confined high pressure. The deformation at room temperature is essentially brittle, cataclastic and mostly accommodated by fracturing on {111} plane with no plastic yielding at uniaxial strains up to 15%. At elevated temperatures of 1000°C and 1200°C diamond crystals exhibit significant ductile flow with corresponding yield strength of 7.9 and 6.3 GPa, indicating that diamond starts to weaken when temperature is over 1000°C. At high temperature the plastic deformation and ductile flow is meditated by the <110>{111} dislocation glide and a very active {111} micro-twinning.
Room-temperature (RT) solid-state sodium-sulfur batteries (SSNSBs) are one of the most promising next-generation energy storage systems because of their high energy density, enhanced safety, cost-efficiency, and non-toxicity. While most of the studies for SSNSBs focused on designing and developing sulfur cathodes, we carve out a new path to understanding and modulating the structures and properties of sulfide solid-state electrolytes (SSEs) for achieving high-performance SSNSBs. A novel cation and anion co-doped approach was developed to enhance the ionic conductivity and expand the electrochemical stability of sulfide SSEs, and eventually improve the electrochemical performance of SSNSBs. The crystal structure and local structure of the cation/anion co-doped sulfide SSEs have been studied in detail combined with the density functional theory (DFT) calculations for mechanism understanding. SSNSBs incorporating co-doped sulfide SSEs demonstrate high capacity and stable cycling performance, even at high rates, which is at the top of the reported performances in the literature. Our novel approach for cation and anion-tuned SSEs demonstrates excellent ionic conductivity and electrochemical stability, paving a new way for the next generation of solid-state sodium batteries.
Silver micro- and nanocrystals with sizes of ∼2−3.5 μm and ∼50−100 nm were uniaxially compressed under nonhydrostatic pressures (strong deviatoric stress) up to ∼30 GPa at room temperature in a symmetric diamond-anvil cell and studied in situ using angle-dispersive synchrotron X-ray diffraction. A cubic to trigonal structural distortion along a 3-fold rotational axis was discovered by careful and comprehensive analysis of the apparent lattice parameter and full width at half-maximum, which are strongly dependent upon the Miller index and crystal size.
Recently, A2B3 type strong spin orbital coupling compounds such as Bi2Te3, Bi2Se3 and Sb2Te3 were theoretically predicated to be topological insulators and demonstrated through experimental efforts. The counterpart compound Sb2Se3 on the other hand was found to be topological trivial, but further theoretical studies indicated that the pressure might induce Sb2Se3 into a topological nontrivial state. Here, we report on the discovery of superconductivity in Sb2Se3 single crystal induced via pressure. Our experiments indicated that Sb2Se3 became superconductive at high pressures above 10 GPa proceeded by a pressure induced insulator to metal like transition at ~3 GPa which should be related to the topological quantum transition. The superconducting transition temperature (TC) increased to around 8.0 K with pressure up to 40 GPa while it keeps ambient structure. High pressure Raman revealed that new modes appeared around 10 GPa and 20 GPa, respectively, which correspond to occurrence of superconductivity and to the change of TC slop as the function of high pressure in conjunction with the evolutions of structural parameters at high pressures.
A comparative phase transition study of nanocrystalline and micro-TiO2 has been conducted under high pressure–temperature (P–T) conditions using energy-dispersive synchrotron x-ray diffraction (XRD). Our study reveals that on compression at room temperature, the micro-tetragonal anatase-type TiO2 started to transform to the orthorhombic columbite-type TiO2 near 1.6 GPa. In contrast, we did not observe this phase transition in nano-anatase at pressures of up to 8.5 GPa. At 8.5 GPa, by applying moderate heat, both samples were transformed completely to columbite-type TiO2 almost simultaneously, indicating that heat treatment could significantly expedite this phase transition. These columbite-type TiO2 phases were quenchable because after cooling them to room temperature and decompressing them to 2.0 GPa, the XRD patterns displayed no changes in comparison with those collected at 8.6 GPa and 1270 K. At 2 GPa, we heated the specimens again, and the rutile-type TiO2 started to emerge around 970 K. This phase was also quenchable after cooling and releasing pressure to ambient conditions. The grain size effects on the phase transition were discussed based on the kinetics mechanism. This study should be of considerable interest to the fields of materials science and condensed matter.
The elastic properties of jarosite were investigated using synchrotron X-ray diffraction coupled with a multi-anvil apparatus at pressures up to 8.1 GPa. With increasing pressure, the c dimension contracts much more rapidly than a, resulting in a large anisotropy in compression. This behavior is consistent with the layered nature of the jarosite structure, in which the (001) [Fe(O,OH)6]/[SO4] sheets are held together via relatively weak K-O and hydrogen bonds. Fitting of the measured unit-cell parameters to the second-order Birch-Murnaghan equation of state yielded a bulk modulus of 55.7 ± 1.4 GPa and zero-pressure linear compressibilities of 3.2 × 10-3 GPa-1 for the a axis and 13.6 × 10-3 GPa-1 for the c axis. These parameters represent the first experimental determination of the elastic properties of jarosite.
In-situ time-of-flight neutron powder diffraction and electrical resistance measurements are performed to determine the behaviors of PbS under pressure and temperature up to 5 GPa and 773 K. The phase diagram in our experimental range is shown based on electrical resistance measurements. Both the two approaches indicate that only the starting cubic PbS phase remains stable when the temperature reaches above 573 K. The Rietveld refinements of the neutron diffraction patterns verify that the orthorhombic (ortho) PbS phase has a Cmcm space group. The fitting of experimental data with the Birch–Murnaghan equation of state at 300 K, yields the bulk modulus of the cubic phase as K0T = 60.0 ± 0.5 GPa with its pressure derivative K0′ fixed to 4.2.
Abstract We conducted hydrothermal experiments at 300°C and at pressure varying from 2.2 to 3.4 kbar to study the effect of fluid salinity on the coupling between molecular hydrogen (H 2 ) formation and olivine serpentinization, where peridotite and olivine with 25–50 μm of starting grain sizes were reacted with pure H 2 O and saline solutions (0.5, 1.5, and 3.3 M NaCl). Serpentine, the main hydrous mineral in most experiments, was quantified according to calibration curves based on Fourier‐transformed infrared spectroscopy and X‐ray diffraction analyses. Compared to pure H 2 O, saline solutions promote the hydrothermal alteration of olivine and peridotite. For experiments with peridotite and pure H 2 O, 67% of reaction extent was achieved after 14 days, which increased to 89% in experiments with medium‐salinity solutions (1.5 M NaCl) over the same period. Medium‐ and high‐salinity solutions inhibit H 2 formation during serpentinization, which is associated with the serpentinization of pyroxene especially clinopyroxene. The redox conditions were constrained according to the equilibrium H 2,aq = H 2,g , and very reducing conditions were achieved during the serpentinization of olivine and peridotite. This study is the first to show iowaite formation directly from peridotite serpentinization, indicating alkaline solutions. Thermodynamic calculations suggest that the hydrolysis of NaCl (NaCl + H 2 O = HCl + NaOH) may yield alkaline solutions, due to higher dissociation constants of NaOH compared to HCl. This study suggests that chlorine greatly influences the serpentinization of olivine and peridotite in natural geological settings. It also indicates that iowaite formation may not require oxidizing conditions as previously thought.
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