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Thestructure of the nanoporous metal–organic frameworkCu3(BTC)2(BTC = 1,3,5-benzenetricarboxylate)with a variety of molecular guests was studied in situusing single crystal X-ray diffraction. By collecting crystal structuredata for a series of guests within the same host crystal, insightsinto the molecular interactions underpinning guest adsorption processeshave been gained. Adsorption behaviors are influenced strongly byboth enthalpic and entropic thermodynamic, as well as interpore steric(size-exclusion) effects, and we note correlations between guest attributesand these effects. Vapor adsorption measurements revealed a guestuptake capacity inversely proportional to guest size. Correspondingly,structural results show that guests reside in the smallest pores accessibleto them. Interpore steric effects for larger guests cause these tobe excluded from the smallest pores, and this corresponds to lowertotal uptake. Both hydrophilic and lipophilic small guests adsorbfavorably into the 5 Å diameter smallest pore of the material,with the number of guests in these pores dependent on guest size andtheir location, in turn dependent upon both guest–guest interactionsand competition between hydrogen-bonding interactions at the aperturesof the smallest pore and lipophilic interactions at the center ofthe smallest pore. Hydrophilic guests with lone electron pairs interactpreferentially with the coordinatively unsaturated Cu sites of thedesolvated framework, with the number of these depending on stericinteractions between neighboring bound guests and guest flexibility.Guest coordination at the Cu sites has a significant effect on theframework structure, increasing the Cu···Cu distancein the dinuclear unit, with the Cu3(BTC)2unitcell being smaller when guests that do not coordinate with the Cuare present, and in the case of cyclohexane, smaller than for thedesolvated framework. Overall, our comprehensive structural studyreconciles Cu3(BTC)2adsorption properties withthe underlying guest–host and guest–guest interactionsthat gives rise to these. [ABSTRACT FROM AUTHOR]

We used in situ neutron powder diffraction(NPD) to study the migrationof Li in Li4Ti5O12anodes with differentparticle sizes during battery cycling. The motivation of this workwas to uncover the mechanism of the increased capacity of the batterymade with a smaller-particle-sized anode. In real time, we monitoredthe anode lattice parameter, Li distribution, and oxidation stateof the Ti atom, and these suggested an increase in the rate of Liincorporation into the anode rather than a change in the migrationpathway as a result of the particle size reduction. The lattice ofthese anodes during continuous lithiation undergoes expansion followedby a gradual contraction and then expansion again. The measured latticeparameter changes were reconciled with Li occupation at specific siteswithin the Li4Ti5O12crystal structure,where Li migrates from the 8ato 16csites. Despite these similar Li-diffusion pathways, in larger-particle-sizedLi4Ti5O12the population of Li atthe 16csite is accompanied by Li depopulation fromthe 8asite, which is in contrast to the smaller-particle-sizedanode where our results suggest that Li at the 8asite is replenished faster than the rate of transfer of Li to the16csite. Fourier-difference nuclear density mapsof both anodes suggest that 32esites are involvedin the diffusion pathway of Li. NPD is again shown to be an excellenttool for the study of electrode materials for Li-ion batteries, particularlywhen it is used to probe real-time crystallographic changes of thematerials in an operating battery during charge–discharge cycling. [ABSTRACT FROM AUTHOR]

Quasielastic neutron scattering was used to study the hydration reaction of tricalcium and dicalcium silicate mixtures by following the fixation of hydrogen into the reaction products, and by applying hydration models to the data. The reaction kinetics were well-described by an Avrami-derived model for the nucleation and growth regime during early hydration times and a diffusion-limited model for later periods. This study showed that the hydration reaction is not a simple linear combination of the reactions for the individual components. Compressive strength tests correlated with the neutron scattering data, suggesting that the details of the interaction affect the microstructure and therefore the strength of the product. Results suggest that favorable reaction mechanics provide optimal strength when an 80−95% tricalcium silicate and 20−5% dicalcium silicate mixture is used. [ABSTRACT FROM AUTHOR]

The article reveals the location of six D2 binding sites in Cu3(BTC)2 using neutron powder diffraction. Researchers also describe an intricate filling order of the framework. Cu3(BTC)2 has a complex three-dimensional channel system. Neutron powder diffraction data are collected on it in a vanadium can using a high-resolution neutron powder diffractometer.

Lithium-rich metal oxides Li1+zMO2 (M = Ni, Co Mn, etc.) are promising positive electrode materials for high-energy lithium-ion batteries, with capacities of 250-300 mAh·g-1 that closely approach theoretical intercalation limits. Unfortunately, these materials suffer severe capacity fade on cycling, among other performance issues. While ion substitution can improve the performance of many of these materials, the underlying mechanisms of property modification are not completely understood. In this work we show enhanced performance of the Li1+zMO2 electrode, consisting of Li2MnO3 (with C2/m space group) and LiMO2 (with R3̄m space group) phases, and establish the effects of cationic and anionic substitution on the phase and structure evolution underpinning performance changes. While the undoped material has a high capacity of ~270 mAh·g-1, only 79% of this remains after 200 cycles. Including ~2% Cr in the material, likely at the R3̄m metal (3a) site, improved cycle performance by ~13%, and including ~5% F in the material, likely at the R3̄m oxygen (6c) site, enhanced capacity by ~4-5% at the expense of a ~12% decline in cycle performance. Moreover, Cr doping enhances energy density retention by ~13%, and F doping suppresses this by 17%. We find that these changes arise by different mechanisms. Both anionic and cationic substitution promote faster Li diffusion, by 48% and 20%, respectively, as determined using cyclic voltammetry and leading to better rate performance. Unlike anionic substitution, cationic substitution enhances structural stability at the expense of some capacity, by suppressing lattice distortion during Li insertion and extraction. This work implicates strategic cationic-anionic codoping for enhanced electrochemical performance in lithium-rich layered metal-oxide phases. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries are the next-generation in battery technology; however, their commercial development is hampered by electrode performance. The P2-type Na2/3(Fe½Mn½)O2 with a hexagonal structure and P63/mmc space group is considered a candidate sodium-ion battery cathode material due to its high capacity (∼190 m Ah·g-1) and energy density (∼520 m Wh·g-1), which are comparable to those of the commercial LiFePO4 and LiMn2O4 lithium-ion battery cathodes, with previously unexplained poor cycling performance being the major barrier to its commercial application. We use operando synchrotron X-ray powder diffraction to understand the origins of the capacity fade of the Na2/3(Fe½Mn½)O2 material during cycling over the relatively wide 1.5-4.2 V (vs Na) window. We found a complex phase-evolution, involving transitions from P63/mmc (P2-type at the open-circuit voltage) to P63 (OP4-type when fully charged) to P63/mmc (P2-type at 3.4-2.0 V) to Cmcm (P2-type at 2.0-1.5 V) symmetry structures during the desodiation and sodiation of the Na2/3(Fe½Mn½)O2 cathode. The associated large cell-volume changes with the multiple two-phase reactions are likely to be responsible for the poor cycling performance, clearly suggesting a 2.0-4.0 V window of operation as a strategy to improve cycling performance. We demonstrated here that the P2-type Na2/3(Fe½Mn½)O2 cathode is able to deliver ∼25% better cycling performance with the strategic operation window. This significant improvement in cycling performance implies that by characterizing the phase evolution and reaction mechanisms during battery function we are able to propose these modifications to the conditions of battery use that improve performance, highlighting the importance of the interplay between structure and electrochemistry. [ABSTRACT FROM AUTHOR]

The mechanism of capacity fade of the Li2MnO3·LiMO2 (M = Li, Ni, Co, Mn) composite positive electrode within a full cell was investigated using a combination of operando neutron powder diffraction and transmission X-ray microscopy methods, enabling the phase, crystallographic, and morphological evolution of the material during electrochemical cycling to be understood. The electrode was shown to initially consist of 73(1) wt % R3m LiMO2 with the remaining 27(1) wt % C2/m Li2MnO3 likely existing as an intergrowth. Cracking in the Li2MnO3·LiMO2 electrode particle under operando microscopy observation was revealed to be initiated by the solid-solution reaction of the LiMO2 phase on charge to 4.55 V vs Li+/Li and intensified during further charge to 4.7 V vs Li+/Li during the concurrent two-phase reaction of the LiMO2 phase, involving the largest lattice change of any phase, and oxygen evolution from the Li2MnO3 phase. Notably, significant healing of the generated cracks in the Li2MnO3·LiMO2 electrode particle occurred during subsequent lithiation on discharge, with this rehealing being principally associated with the solid-solution reaction of the LiMO2 phase. This work reveals that while it is the reduction of lattice size of electrode phases during charge that results in cracking of the Li2MnO3·LiMO2 electrode particle, with the extent of cracking correlated to the magnitude of the size change, crack healing is possible in the reverse solid-solution reaction occurring during discharge. Importantly, it is the phase separation during the two-phase reaction of the LiMO2 phase that prevents the complete healing of the electrode particle, leading to pulverization over extended cycling. This work points to the minimization of behavior leading to phase separation, such as two-phase and oxygen evolution, as a key strategy in preventing capacity fade of the electrode. [ABSTRACT FROM AUTHOR]

The favorable combination of fast-ionic conductivity and high electrochemical stability of Li-stuffed garnet type Li7La3Zr2O12 (LLZ) makes this material a promising candidate for applications as a solid-state electrolyte in high-energy-density batteries. However, a widespread technical use of LLZ is impeded by difficulty in reliable formation and densification of the pure fast-ion conducting phase. The present study of the phase-formation process enables rational fabrication procedures to be devised based on a thorough understanding of the complex phase formation of LLZ. In situ neutron powder diffraction monitoring of the phase formation revealed an influence of the partial melting of precursors on the formation of the fast-ion conducting phase, indicating that in the typical synthesis route LLZ is not formed in a solid-state reaction but from a partial carbonate melt that decomposes on further heating. The cooling rate critically influences lithium ordering and ionic conductivity. [ABSTRACT FROM AUTHOR]

An ultramicroporous metal–organicframework (MOF) is reportedthat contains 0.35 nm nanotube-like channels with an unprecedentedconcentration of vacant CuIIcoordination sites. The nonintersecting,narrow channels in [Cu3(cdm)4] (cdm = C(CN)2(CONH2)−) align in two perpendiculardirections, structurally resembling copper-doped carbon nanotubeswith CuIIembedded in the walls of the channels. The combinationof ultramicroporosity with the exposed CuIIcoordinationsites gives size-based selectivity of CO2over CH4, based on pore-size distribution and modeling. Neutron powder diffractionand molecular dynamics simulations show the close packing of singlerows of guests within the tubular nanostructure and interaction ofCO2with the exposed metal sites. [ABSTRACT FROM AUTHOR]

Yeelimite, Ca4[Al6O12]SO4, is outstanding as an aluminatesodalite, being the framework ofthese type of materials flexible and dependent on ion sizes and anionordering/disordering. On the other hand, yeelimite is also importantfrom an applied perspective as it is the most important phase in calciumsulfoaluminate cements. However, its crystal structure is not wellstudied. Here, we characterize the room temperature crystal structureof stoichiometric yeelimite through joint Rietveld refinement usingneutron and X-ray powder diffraction data coupled with chemical soft-constraints.Our structural study shows that yeelimite has a lower symmetry thanthat of the previously reported tetragonal system, which we establishto likely be the acentric orthorhombic space group Pcc2, with a √2a × √2a × a superstructure basedon the cubic sodalite structure. Final unit cell values were a= 13.0356(7) Å, b= 13.0350(7) Å,and c= 9.1677(2) Å. We determine several structuresusing density functional theory calculations, with the lowest energystructure being Pcc2 in agreement with our experimentalresult. Yeelimite undergoes a reversible phase transition to a higher-symmetryphase which has been characterized to occur at 470 °C by thermodiffractometry.The higher-symmetry phase is likely cubic or pseudocubic possessingan incommensurate superstructure, as suggested by our theoreticalcalculations which show a phase transition from an orthorhombic toa tetragonal structure. Our theoretical study also predicts a pressure-inducedphase transition to a cubic structure of space group I43m. Finally, we show thatour reported crystal structure of yeelimite enables better mineralogicalphase analysis of commercial calcium sulfoaluminate cements, as shownby RFvalues for this phase, 6.9% and 4.8% for the previouslypublished orthorhombic structure and for the one reported in thisstudy, respectively. [ABSTRACT FROM AUTHOR]

Lithium-ionbatteries are undergoing rapid development to meetthe energy demands of the transportation and renewable energy-generationsectors. The capacity of a lithium-ion battery is dependent on theamount of lithium that can be reversibly incorporated into the cathode.This work directly quantifies the time- and current-dependent lithiumtransfer within a cathode functioning under conventional charge–dischargecycling. We examine Li1+yMn2O4under real working conditions using in situ neutronpowder diffraction and link the atomic-scale structure to the batteryperformance. The lithium location and content, oxygen positional parameter,and lattice parameter of the cathode are measured and linked to thebattery’s charge/discharge characteristics. Lithium insertion(discharge) differs from extraction (charge), a feature that may explainthe relative ease of discharge (compared with charge) of this material.An atomic-scale understanding of cathode functionality, such as revealedhere, will direct improvements in battery performance at both thepractical and the fundamental level. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries power many portable devices and in the future are likely to play a significant role in sustainable-energy systems for transportation and the electrical grid. LiFePO4 is a candidate cathode material for second-generation lithium-ion batteries, bringing a high rate capability to this technology. LiFePO4 functions as a cathode where delithiation occurs via either a solid-solution or a two-phase mechanism, the pathway taken being influenced by sample preparation and electrochemical conditions. The details of the delithiation pathway and the relationship between the two-phase and solid-solution reactions remain controversial. Here we report, using real-time in situ neutron powder diffraction, the simultaneous occurrence of solid-solution and two-phase reactions after deep discharge in nonequilibrium conditions. This work is an example of the experimental investigation of nonequilibrium states in a commercially available LiFePO4 cathode and reveals the concurrent occurrence of and transition between the solid-solution and two-phase reactions. [ABSTRACT FROM AUTHOR]

The air-free reaction between FeCl2 and H4dobdc (dobdc4- = 2,5-dioxido-1,4-benzenedicarboxylate) in a mixture of N,N-dimethylformamide (DMF) and methanol affords Fe2(dobdc)·4DMF, a metal-organic framework adopting the MOF-74 (or CPO-27) structure type. The desolvated form of this material displays a Brunauer-Emmett-Teller (BET) surface area of 1360 m²/g and features a hexagonal array of one-dimensional channels lined with coordinatively unsaturated FeII centers. Gas adsorption isotherms at 298 K indicate that Fe2(dobdc) binds O2 preferentially over N2, with an irreversible capacity of 9.3 wt %, corresponding to the adsorption of one O2 molecule per two iron centers. Remarkably, at 211 K, O2 uptake is fully reversible and the capacity increases to 18.2 wt %, corresponding to the adsorption of one O2 molecule per iron center. Mossbauer and infrared spectra are consistent with partial charge transfer from iron(II) to O2 at low temperature and complete charge transfer to form iron(III) and O22- at room temperature. The results of Rietveld analyses of powder neutron diffraction data (4 K) confirm this interpretation, revealing O2 bound to iron in a symmetric side-on mode with dO-O = 1.25(1) Å at low temperature and in a slipped side-on mode with dO-O = 1.6(1) Å when oxidized at room temperature. Application of ideal adsorbed solution theory in simulating breakthrough curves shows Fe2(dobdc) to be a promising material for the separation of O2 from air at temperatures well above those currently employed in industrial settings. [ABSTRACT FROM AUTHOR]

Because of its stability, nanosized olivine LiFePO4 opens the door toward high-power Li-ion battery technology for large-scale applications as required for plug-in hybrid vehicles. Here, we reveal that the thermodynamics of first-order phase transitions in nanoinsertion materials is distinctly different from bulk materials as demonstrated by the decreasing miscibility gap that appears to be strongly dependent on the overall composition in LiFePO4. In contrast to our common thermodynamic knowledge, that dictates solubility limits to be independent of the overall composition, combined neutron and X-ray diffraction reveals strongly varying solubility limits below particle sizes of 35 nm. A rationale is found based on modeling of the diffuse interface. Size confinement of the lithium concentration gradient, which exists at the phase boundary, competes with the in bulk energetically favorable compositions. Consequently, temperature and size diagrams of nanomaterials require complete reconsideration, being strongly dependent on the overall composition. This is vital knowledge for the future nanoarchitecturing of superior energy storage devices as the performance will heavily depend on the disclosed nanoionic properties. [ABSTRACT FROM AUTHOR]