Crystalline Host Research Articles

Azeotropic clathrate: Compelling similarity of CO2 and N2O uptake in an organic crystalline host

Both CO2 and N2O are greenhouse gases (GHGs) notorious for their impact on climate change. Because they threaten the future of human beings, they must be captured and recovered from the perspective of environmental protection. Herein, we evaluate the potential feasibility of using hydroquinone (HQ) clathrate formed from CO2-N2O gas mixtures for storage and recovery of GHGs. Structural characteristics and guest-occupation behaviors of the HQ samples reacted with CO2-N2O gas mixtures at room temperature were investigated using X-ray diffraction, scanning electron microscopy, Raman spectroscopy, infrared spectroscopy, and solid-state NMR. The combined results via these measurements indicate that all the HQ samples formed from CO2-N2O gas mixtures were β-HQ clathrate structures. The gas storage capacity of the β-HQ clathrates and the cage occupancy of guest molecules were found to be 60.2–62.3 cm3 g−1 and 0.82–0.84, respectively. Selectivity measurements indicate that the β-HQ clathrate reveals azeotropic-like behavior for all gas compositions, showing no preferential occupation by CO2 or N2O in the cages of β-HQ clathrate. The compositions of CO2 and N2O in the β-HQ clathrates are very close to the initial gas compositions. This indicates that this CO2-N2O-loaded β-HQ clathrate is the first example of an all-composition azeotropic clathrate. Kinetics experiments demonstrate that the azeotropic β-HQ clathrates are attributable to very similar formation kinetics of β-HQ clathrates with CO2 and with N2O guest molecules. These results provide useful knowledge of host–guest and guest–guest interactions in clathrate compounds and novel applications of β-HQ clathrates. These will be adopted to develop further a clathrate-based GHG storage and recovery technology.

Potential impact of cementitious leachates on the buffer porewater chemistry in the Finnish repository for spent nuclear fuel – A reactive transport modelling assessment

Cementitious materials will be used during the construction and operation of a geological repository for spent nuclear fuel at Olkiluoto in Finland. Upon contacting water, cement dissolution will generate high-pH leachates, which might eventually reach the proximity of a canister deposition hole through an interconnected network of fractures in the crystalline host rock. Highly-alkaline conditions near the bentonite buffer surrounding the canister could affect the performance of the buffer safety functions. In this study, we evaluate the potential impact such cement leachates might have on the chemical composition of the buffer porewater over time-frames relevant for the safety assessment of the repository.Although a comprehensive mechanistic assessment of these interactions is not possible due to their complexity, we demonstrate that key processes and their impact on the chemical composition of the bentonite porewater can be bounded. To this end we apply a reactive transport modelling based on an analysis of processes and parameter values. The model considers a 3D geometry including: the canister, the bentonite buffer, and a discrete fracture in the rock intersecting the deposition hole. Cement leachates flow through the fracture around the deposition hole, while solutes exchange with the buffer porewater via advective and diffusive mass transfer.Modelling results indicate that a combination of restricted water flow within the fracture, slow diffusive solute transport in the buffer, and chemical reactions will act together to minimise the extent of buffer porewater perturbation, should cement leachates reach the vicinity of a deposition hole. The model pessimistically estimates a maximum pH variation to be below 0.1 unit, and a maximum concentration change of about factor 3 (relative to initial) for reacting components within most of the buffer volume. This is only about double the perturbation values predicted for “natural” evolution of the buffer porewater, in the absence of cement leachates.Model uncertainties are evaluated by a series of sensitivity cases. These calculations suggest that additional processes, not directly accounted for in the base model (such as leachate-groundwater mixing and dilution on transport through the fracture network, and porosity reduction in the buffer due to mineral precipitation), could significantly contribute to a further reduction of the magnitude of potential buffer porewater perturbation.

Crystal structures of Val58Ile tryptophan repressor in a domain-swapped array in the presence and absence ofL-tryptophan

The crystal structures of domain-swapped tryptophan repressor (TrpR) variant Val58Ile before and after soaking with the physiological ligand L-tryptophan (L-Trp) indicate that L-Trp occupies the same location in the domain-swapped form as in native dimeric TrpR and makes equivalent residue contacts. This result is unexpected because the ligand binding-site residues arise from three separate polypeptide chains in the domain-swapped form. This work represents the first published structure of a domain-swapped form of TrpR with L-Trp bound. The presented structures also show that the protein amino-terminus, whether or not it bears a disordered extension of about 20 residues, is accessible in the large solvent channels of the domain-swapped crystal form, as in the structures reported previously in this form for TrpR without N-terminal extensions. These findings inspire the exploration of L-Trp analogs and N-terminal modifications as labels to orient guest proteins that cannot otherwise be crystallized in the solvent channels of crystalline domain-swapped TrpR hosts for potential diffraction analysis.

Impact of rock fracture geometry on geotechnical barrier integrity – A numerical study

The effect of fracture geometry on bentonite erosion for a generic repository site in crystalline host rock environment was investigated by means of 2-d numerical simulations. Fracture geometry was varied systematically using random aperture normal distributions with a mean aperture of 1 mm and standard deviations between 0 and 0.7 mm, respectively. Moreover, two aperture correlation lengths (0.2 m and 2 m) were applied. Based on the synthetic fracture aperture fields generated the cubic law in conjunction with the Darcy equation is used to simulate fracture flow fields for mean flow velocities in the fracture between 1 × 10−5 m/s and 1 × 10−7 m/s. These flow fields are used in a two-way coupling approach to bentonite erosion simulations.The results of the study clearly show the influence of variable fracture aperture on bentonite erosion behaviour and erosion rates (kg/a). Increasing fracture aperture standard deviation leads to increasing heterogeneous flow velocity distributions governing the erosion behaviour and erosion rates. Calculated steady state erosion rates are in the range of ~0.25 kg/a down to ~0.014 kg/a. The highest erosion rate is calculated for the highest mean flow velocity in conjunction with the highest standard deviation. The effect of aperture heterogeneity diminishes for the lowest flow velocities.In summary, the results show the effect of fracture heterogeneity on bentonite erosion, especially for high to medium mean flow velocities combined with high to medium fracture heterogeneity under the model boundary conditions and model capabilities and limitations considered. An increase of up to ~83% in erosion rate compared to the constant aperture case highlights the need to consider fracture aperture heterogeneity and its effect on the bentonite erosion in the assessment of the safety and evolution of a high-level nuclear waste repository.

Low‐Overpotential LiF Splitting in Lithiated Fluoride Conversion Cathode Catalyzed by Spinel Oxide

AbstractConversion chemistry involving LiF splitting is an appealing route toward high capacity cathodes for Li‐ion batteries. In general, cathodes based on LiF splitting need a redox host to provide the driving force for LiF decomposition from the surface. However, most of the systems are still far from practical owing to their limitations, especially the high charge voltage (4.5–5.0 V) needed to fully utilize the capacity and the subsequent low energy efficiency (<80%). The redox host is apparently the key to further reduce the required charge voltage and improve the energy efficiency. Here, a new LiF–NiFe2O4 conversion cathode chemistry is designed and demonstrated with a crystalline spinel oxide redox host. It is demonstrated that the new host effectively improves the surface redox and LiF splitting kinetics, which enable the new cathode to work at much lower charge cutoff voltage (4.2 V) without compromising the delivered capacity and voltage. The LiF–NiFe2O4 composite thin film is able to be discharged with large capacity of 237 mA h g−1 with high energy efficiency (88%), substantial pseudocapacitance contribution (>90%), and satisfactory capacity retention. This result indicates LiF splitting chemistry can become practical by carefully tailoring the redox host chemistry and optimizing the composition.

Numerical analysis of coupled hydro-mechanical and thermo-hydro-mechanical behaviour in buffer materials at a geological repository for nuclear waste: Simulation of EB experiment at Mont Terri URL and FEBEX at Grimsel test site using Barcelona basic model

We investigated the applicability of a thermo-elasto-plastic model using a TOUGH2-MP/FLAC3D simulator to reproduce the coupled hydro-mechanical behaviour at the engineered barrier emplacement experiment in Opalinus Clay and the coupled thermo-hydro-mechanical behaviour at the full-scale engineered barrier experiment in a crystalline host rock, as part of the DECOVALEX-2019 project Task D. In the numerical models, we adopted Darcy's law, Fick's law, and Fourier's law for the advective flux of fluid, vapour diffusion, and conductive heat flux, respectively. We also used the mechanical constitutive law, which explicitly considers the effects of temperature, pore pressure, suction, and strain changes using the elastic model and the Barcelona basic model. In general, the numerical models in the simulator successfully represented the coupled behaviour in bentonite buffer materials at the two long-term in situ experiments in terms of evolution and spatial distribution for temperature, relative humidity, total stress, and displacement. The performance of the models for the dismantling of the in-situ experiments is globally satisfactory compared with the post-mortem results for saturations, water contents, and dry density.

Structural distortion induced enhancement in UV-C emitting properties of Pr3+-activated La-substituted yttrium phosphates (Y1-xLaxPO4:Pr3+)

The UV-C emission with a spectral range of 200–280 nm is of paramount importance in the germicidal and medical applications for disinfection, sterilization, and deactivation of microorganisms such as bacteria and virus considering current global pandemic crisis of coronavirus (COVID-19). Such intense UV-C radiation (4.4–6.2 eV) can be often generated using Pr3+ activators (as a result of their electronic transition [Xe]4f15d1→[Xe]4f2) doped in crystalline inorganic host matrices. In this regard, Pr3+-activated rare earth phosphates have been intensively studied as a model system of UV-C emitters thus far. Here, we have prepared three different representative crystalline UV-C phosphors of YPO4:Pr3+ (tetragonal), LaPO4:Pr3+ (monoclinic), and La-substituted YPO4:Pr3+ (tetragonal), respectively, and further investigated the effect of La substitution in YPO4 crystal structures on UV-C emitting properties. The structural lattice distortion in the local environment of activator Pr3+ cations induced by La substitution indeed impacts on the UV-C emitting properties. Small amount of substitutional doping of La3+ (ca. 5 mol.%) in Y site of YPO4 enhances the UV-C emission intensity by a two-fold of magnitude recorded under 225 nm excitation (photoluminescence) and cathode ray (cathodeluminescence). This finding can provide a fundamental designing principle of inorganic phosphor materials to enhance the emitting properties of activators, directly influenced by local environment and symmetry of the crystal structures.

Control of Guest Thermal Release by Crystalline Host Orientation

Thermal release of guest molecules from poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) films, exhibiting host–guest co-crystalline (CC) phases with orientation of their chain axes being preferentially...

A phase-convertible fast ionic conductor with a monolithic plastic crystalline host

We present a fast Mg2+-ion conductor with a monolithic plastic crystalline host. Also, conformal contact with a solid electrode can be achieved by using the reversible phase transition of succinonitrile through simple heating and cooling processes.

Influence of crystalline mediums KCl and KDP on structural and optical properties of embedded CdSe quantum dots

In order to pass comfortably to the practicalities of nanomaterials it is necessary to use, in general, a support like: films, amorphous hosts or crystalline hosts. So it is important to know the effect of hosts on structural and optical properties of nanomaterials, in this context, this investigation suggests to survey the behavior of CdSe quantum dots (QDs) dispersed in two different crystalline hosts the potassium chlorade KCl and the potassium Di-hydrogen phosphate KH2PO4 (KDP) single crystals, where they are prepared using tow different technics: the Czochralski (Cz) method and the lowering temperature from aqueous solution technic, respectively. The obtained results from X-ray diffraction (XRD) demonstrate that CdSe QDs have different preferred orientations inside these two hosts. This behavior will be discussed in detail. Nevertheless, the UV–vis and Phtoluminiscance (PL) spectroscopy prove that the optical properties of CdSe QDs have great similarity in these two hosts.

A microwave-triggered opening of the multifunctional polyelectrolyte capsules with nanodiamonds in the shell composition

Microcapsules are ideal cargo platform for variety of applications such as drug delivery, sensing and imaging due to the combination of a simplicity fabrication and flexibility in the design. We developed remotely collapsing polymer capsules to response to external microwave treatment. The multilayer structure of the capsules was designed to create a polyfunctional system intercalating with nanodiamonds (NDs) and upconversion nanoparticles (UCNPs) into the polyelectrolyte shell. NDs empower local overheating to the microcapsules, while UCNPs provide opportunity to luminescent thermal sensing. UCNPs consist of inorganic crystalline host matrix - hexagonal β-phase NaYF4, doped with pairs of trivalent lanthanide ions, which play role of sensitizer (Yb3+) and activator (Er3+). The microwave triggering followed by the capsule heating results in the controlled destruction of the polyelectrolyte shell with subsequent cargo release. UCNPs luminescence was utilized to determine the local temperature of the capsule shell at nanoscale under GHz ultrasonic treatment. Our novel approach provides on demand microcapsule system destruction, which can be used in the development of nanotheranostic platform for the unification of diagnosis and treatment of various diseases.

Bi3+ assisted enhancement of photoluminescence and thermal sensing of Er3+/Yb3+ co-doped SrGdAlO4 phosphor with unusual stable color

Er3+/Yb3+ co-doped SrGdAlO4 up-conversion phosphors with a tetragonal phase were synthesized using solid state reaction method. The dominant up-conversion luminescent mechanism was deduced through analyzing the power dependencies, energy diagrams and fluorescence lifetimes. It is interesting that the emitting color was almost unchanged when adjusting the dopant contents of Er3+ and Yb3+, excitation power and ambient temperature. The emission intensity and color purity of SrGdAlO4: Er3+, Yb3+ sample can be notably enhanced by introducing Bi3+ ions. X-ray diffraction and band gap analysis illustrated that Bi3+ ions can increase the asymmetric surrounding environment of the SrGdAlO4 host lattice. Simultaneously, the change of microstrain value showed that the host crystalline is affected by Bi3+ ions codoping. Optical temperature sensing performance based on the thermal coupled energy levels 2H11/2 and 4S3/2 of Er3+ ions was evaluated in the visible light region. The absolutely sensitivity of SrGdAlO4: Er3+, Yb3+ and SrGdAlO4: Er3+, Yb3+, Bi3+ are 3.8 × 10−3 K−1 and 6.1 × 10−3 K−1 respectively. The results indicated that codoping Bi3+ ions can improve the luminescent intensity of SrGdAlO4: Er3+, Yb3+, but also strengthen its temperature sensing characteristics.

EPR characterization of erbium in glasses and glass ceramics

Electron paramagnetic resonance (EPR) is a well-established spectroscopic technique for electronic structure characterization of rare-earth ion impurities in crystalline and amorphous hosts. EPR spectra of erbium-doped glass matrices and nanocomposites can provide information about local structure variations induced by changes in chemical composition or crystallization processes. Characterization possibilities of Er3+ ions in glasses and glass ceramics including direct EPR measurements, indirect investigations via secondary paramagnetic probes, and optically detected magnetic resonance techniques are considered in this article.

Phosphorescence Quenching of Heavy-Atom-Free Dopant Chromophores Triggered by Thermally Activated Triplet Exciton Diffusion of a Conjugated Crystalline Host

Persistent room-temperature phosphorescence (pRTP) from aggregated molecular crystalline materials is important for stable high-resolution afterglow imaging. However, an unclear understanding conce...

Schedule of Mafic to Hybrid Magma Injections Into Crystallizing Felsic Magma Chambers and Resultant Geometry of Enclaves in Granites: New Field and Petrographic Observations From Ladakh Batholith, Trans-Himalaya, India

Diorites, granites, and associated magmatic enclaves and dykes constitute the bulk of the Ladakh Batholith, which is an integral part of the Trans-Himalayan magmatic arc system. In this paper, geometry of microgranular enclaves hosted in the granites has been examined from the Leh-Sabu-Chang La and surrounding regions of the eastern Ladakh Batholith to infer the mechanism and schedule of mafic to hybrid magma injections into evolving felsic magma chambers and the resultant enclave geometry. Mafic and/or hybrid magmas injected into felsic magma at low volume fraction ( 0.65) of crystals. A large rheological difference between coeval felsic and mafic magmas inhibits much interaction. Mafic magma progressively crystallizes and evolves while minimizing thermal and rheological differences. Consequently, the felsic-mafic magma interaction process gradually becomes more efficient causing dispersion of enclave magma globules and undercooling into the partly crystalline felsic host magma. Thus, the evolution of the Ladakh Batholith should be viewed as multistage interactions of mafic to hybrid magmas coeval with felsic magma pulses in plutonic conditions from its initial to waning stages of evolution.

Thermal annealing of radiation defects in MgF2 single crystals induced by neutrons at low temperatures

Primary radiation defects in ionic solids consist of Frenkel defects – pairs of defects - anion vacancies with trapped electrons (F-type centers) and interstitial ions. Upon temperature increase after irradiation, the electronic F-type centers are annealed due to recombination with mobile interstitials. Analysis of the recombination (annealing) kinetics allows us to obtain important information on the interstitial migration. At high radiation doses more complex dimer (F2-type) centers are observed in several charge states, which are well distinguished spectroscopically. We analysed here available experimental kinetics of the F2-type center annealing in MgF2 in a wide temperature range (300–1000 K). The results of the electron, neutron and ion irradiation are compared.The phenomenological theory of the recombination kinetics of radiation defects takes into account the interstitial ion diffusion and recombination with the F2-centers as well as mutual sequential transformation with temperature growth of three types of experimentally observed dimer centers: F2 (1); F2 (2), F2 (3) (which differ tentatively by effective charges with respect to the host crystalline sites: 0, +1, +2).

Ytterbium-implanted photonic resonators based on thin film lithium niobate

We introduce our design, simulation, and fabrication for cm-long waveguides and micro-ring resonators based on fully-etched thin-film lithium niobate on insulator (LNOI) incorporated with rare earth ions. We implant ytterbium ions (Yb3+) into the crystalline host and study their optical properties at 4 K temperature. We measure an intrinsic optical quality factor of higher than 2×106 after postimplantation annealing. We characterize the photoluminescence spectrum, lifetime, and absorption of Yb3+ ions. Incorporation of rare earth ions into LNOI as a crystalline and nonlinear photonic element may enable the development of multi-functional quantum photonic devices capable of generating, transducing, manipulating, and storing of quantum optical information.

Exerting Spatial Control During Nanoparticle Occlusion within Calcite Crystals.

In principle, nanoparticle occlusion within crystals provides a straightforward and efficient route to make new nanocomposite materials. However, developing a deeper understanding of the design rules underpinning this strategy is highly desirable. In particular, controlling the spatial distribution of the guest nanoparticles within the host crystalline matrix remains a formidable challenge. Herein, we show that the surface chemistry of the guest nanoparticles and the [Ca2+ ] concentration play critical roles in determining the precise spatial location of the nanoparticles within calcite crystals. Moreover, in situ studies provide important mechanistic insights regarding surface-confined nanoparticle occlusion. Overall, this study not only provides useful guidelines for efficient nanoparticle occlusion, but also enables the rational design of patterned calcite crystals using model anionic block copolymer vesicles.

Luminescent ion-doped transparent glass ceramics for mid-infrared light sources [invited

Glass ceramics (GCs), which consist essentially of a homogeneous solid state dispersion of nanocrystals (NCs) embedded in a chemically inert and mechanically robust glass matrix, appear to be an extremely promising class of solid state materials that can be easily tailored into arbitrary shapes, including a new generation of optical fibers, for efficient incoherent and coherent sources of mid-infrared (MIR) light emission. This unique capability not only stems from the fact that one can tailor the underlying glass matrix for optimal macroscopic physical properties and ultrahigh transparency at the wavelengths of interest (resulting in appropriate "transparent glass ceramics" or TGCs), but also stems from the fact that one can embed these matrices with size and structure-tailored NCs, which in turn can be doped with relatively high concentrations of MIR emitting rare-earth or transition metal ions. This potential is tantamount to the localization of these highly efficient MIR ionic emitters into carefully selected and highly favorable "process-engineered" custom crystalline host "nanocages," while insulating the ionic emitters from the emission-quenching glass host matrix, the latter being chosen largely because of its highly favorable macroscopic bulk properties, including its ductility and formability into near-arbitrary shapes (at appropriate temperatures). Such MIR TGCs appear to be very promising for numerous photonics applications, including compact and relatively efficient waveguide sensors, broadband incoherent MIR light sources, superluminescent light sources, advanced fiber-optic devices, and broadly wavelength-tunable and ultrashort pulse mode-locked fiber and bulk solid-state lasers. In this paper, we review past achievements in this field, starting with an overview of TGCs, followed by discussions of currently preferred methods of fabrication, characterization, and optimization of suitably doped oxyfluoride, tellurite, and chalcogenide TGCs and of our projections of anticipated future developments in this field at both the materials and device levels.

Sensing Individual Nuclear Spins with a Single Rare-Earth Electron Spin.

Rare-earth related electron spins in crystalline hosts are unique material systems, as they can potentially provide a direct interface between telecom band photons and long-lived spin quantum bits. Specifically, their optically accessible electron spins in solids interacting with nuclear spins in their environment are valuable quantum memory resources. Detection of nearby individual nuclear spins, so far exclusively shown for few dilute nuclear spin bath host systems such as the nitrogen-vacancy center in diamond or the silicon vacancy in silicon carbide, remained an open challenge for rare earths in their host materials, which typically exhibit dense nuclear spin baths. Here, we present the electron spin spectroscopy of single Ce^{3+} ions in a yttrium orthosilicate host, featuring a coherence time of T_{2}=124 μs. This coherent interaction time is sufficiently long to isolate proximal ^{89}Y nuclear spins from the nuclear spin bath of ^{89}Y. Furthermore, it allows for the detection of a single nearby ^{29}Si nuclear spin, native to the host material with ∼5% abundance. This study opens the door to quantum memory applications in rare-earth ion related systems based on coupled environmental nuclear spins, potentially useful for quantum error correction schemes.