The mechanical properties and stability of studtite, (UO2)(O2)(H2O)2·2H2O, and metastudtite, (UO2)(O2)(H2O)2, were investigated using density functional perturbation theory.
Phases of the iron–oxygen binary system are significant to most scientific disciplines, directly affecting planetary evolution, life, and technology. Iron oxides have unique electronic properties and strongly interact with the environment, particularly through redox reactions. The iron–oxygen phase diagram therefore has been among the most thoroughly investigated, yet it still holds striking findings. Here, we report the discovery of an iron oxide with formula Fe 4 O 5 , synthesized at high pressure and temperature. The previously undescribed phase, stable from 5 to at least 30 GPa, is recoverable to ambient conditions. First-principles calculations confirm that the iron oxide here described is energetically more stable than FeO + Fe 3 O 4 at pressure greater than 10 GPa. The calculated lattice constants, equation of states, and atomic coordinates are in excellent agreement with experimental data, confirming the synthesis of Fe 4 O 5 . Given the conditions of stability and its composition, Fe 4 O 5 is a plausible accessory mineral of the Earth’s upper mantle. The phase has strong ferrimagnetic character comparable to magnetite. The ability to synthesize the material at accessible conditions and recover it at ambient conditions, along with its physical properties, suggests a potential interest in Fe 4 O 5 for technological applications.
2 ], have been investigated using density functional theory. The structure of metastudtite crystallizing in the orthorhombic space group Pnma (Z = 4) is reported for the first time at the atomic level and the computed lattice parameters, a = 8.45, b = 8.72, c = 6.75 Å, demonstrate that the unit cell of metastudtite is larger than previously reported dimensions (Z = 2) derived from experimental X-ray powder diffraction data.
The interplay between thermodynamics and mechanical properties in the transformation of studtite, (UO2)(O2)(H2O)2·2H2O, into metastudtite, (UO2)(O2)(H2O)2, two important corrosion phases observed on the surface of uranium dioxide exposed to water, is revealed using density functional perturbation theory. Phonon calculations within the quasi-harmonic approximation predict that the standard entropy change for the (UO2)(O2)(H2O)2·2H2O → (UO2)(O2)(H2O)2 + 2H2O reaction is ΔS 0 = +80 J·mol–1·K–1 for the production of water in the liquid state and +389 J·mol–1·K–1 for water vapor. Similar to bulk H2O(l), the bulk modulus of (UO2)(O2)(H2O)2·2H2O increases with temperature, contrasting with (UO2)(O2)(H2O)2 which features the typical Anderson–Gruneisen temperature dependence of oxide solids. Upon removal of interstitial H2O in studtite, the most important changes in the shear modulus, the parameter limiting the mechanical stability, arise in the planes normal to chain propagation directions. The present findings have important implications for the dehydration of other hygroscopic materials.
The authors have performed a systematic computational study of the hydrogen storage capacity of model organometallic compounds consisting of Sc, Ti, and V transition metal atoms bound to CmHm rings (m=4-6). For all the complexes considered, the hydrogen storage capacity is limited by the 18-electron rule. The maximum retrievable H2 uptake predicted is 9.3 wt% using ScC4H4, slightly better than the 9.1 wt% hydrogen using TiC4H4, and much larger than the approximately 7 wt% hydrogen with VC4H4, where only four H2 molecules can be adsorbed. The kinetic stability of these hydrogen-covered organometallic complexes is reviewed in terms of the energy gap between the highest occupied and lowest unoccupied molecular orbitals and the strength and nature of successive H2 bindings.
We combine experimental observations with ab initio calculations to study the reversible hydrogenation of single-wall carbon nanotubes using high boiling polyamines as hydrogenation reagents. Our calculations characterize the nature of the adsorption bond and identify preferential adsorption geometries at different coverages. We find the barrier for sigmatropic rearrangement of chemisorbed hydrogen atoms to be approximately 1 eV, thus facilitating surface diffusion and formation of energetically favored, axially aligned adsorbate chains. Chemisorbed hydrogen modifies the structure and stability of nanotubes significantly and increases the inter-tube distance, thus explaining the improved dispersability in solvents like methanol, ethanol, chloroform, and benzene.
The structure of dehydrated schoepite, α-UO2(OH)2, was investigated using computational approaches that go beyond standard density functional theory and include van der Waals dispersion corrections (DFT-D). Thermal properties of α-UO2(OH)2, were also obtained from phonon frequencies calculated with density functional perturbation theory (DFPT) including van der Waals dispersion corrections. While the isobaric heat capacity computed from first-principles reproduces available calorimetric data to within 5% up to 500 K, some entropy estimates based on calorimetric measurements for UO3·0.85H2O were found to overestimate by up to 23% the values computed in this study.
We investigate the (0001) surface of single crystal quartz with a submonolayer of Rb adsorbates. Using Rydberg atom electromagnetically induced transparency, we investigate the electric fields resulting from Rb adsorbed on the quartz surface, and measure the activation energy of the Rb adsorbates. We show that the adsorbed Rb induces a negative electron affinity (NEA) on the quartz surface. The NEA surface allows low energy electrons to bind to the surface and cancel the electric field from the Rb adsorbates. Our results are important for integrating Rydberg atoms into hybrid quantum systems and the fundamental study of atom-surface interactions, as well as applications for electrons bound to a 2D surface.Due to recent technological advances in fabrication and trapping, hybrid quantum systems (HQS) consisting of atoms and surfaces, as well as electrons and surfaces, are fast emerging as ideal platforms for a diverse range of studies in quantum control, quantum simulation and computing, strongly correlated systems and microscopic probes of surfaces. Miniaturization of chip surfaces is necessary to achieve large platform scalability, but decoherence and noise emerge as serious challenges as feature sizes shrink [1][2][3]. Mitigating the noise is a fundamental and necessary step in realizing the full potential of HQSs for quantum technologies.Combining ultracold Rydberg atoms with surfaces for HQS is attractive because Rydberg atoms can have large sizes, significant electric dipole moments and strong interactions. There have recently been a host of theoretical proposals for utilizing Rydberg atoms near surfaces [4][5][6][7][8]. Progress on the experimental front has been hampered by uncertainties in characterizing interactions of atoms with surfaces, although some recent work in this regards are noteworthy [9][10][11].To take full advantage of Rydberg atom HQSs, a more complete understanding of surfaces is needed. One problem is that Rydberg atoms incident upon metal surfaces can be ionized [12, 13]. A second major hurdle is the background electric fields (Efields) caused by adsorbates [14][15][16][17][18][19]. Rydberg states are sensitive to adsorbate E-fields because they are highly polarizable [20]. Adsorbate E-fields have caused problems for other experiments as well, including Casimir-Polder measurements [21], and surface ion traps [22]. A possible solution is to minimize the E-fields by canceling them out.A convenient surface for applications in HQSs is quartz because of its extensive use in the semiconductor and optics industries. Despite numerous theoretical and experimental studies of bulk SiO 2 [23-25], the surface properties are not well understood. Recent theoretical work has focused on surface reconstruction and the adsorption of water and graphene [26][27][28][29][30]. The (0001) surface has been the subject of recent theoretical interest, partially due to its stability and low surface energy [26,30].In this work, we show that adsorption of Rb atoms on a quartz (SiO 2 (0001)) surface, contrary to prev...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.