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Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations
Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations
Unidirectional magnetoresistance (UMR) in a bilayer heterostructure, consisting of a spin-source material and a magnetic layer, refers to a change in the longitudinal resistance on the reversal of magnetization and originates from the interaction of non-equilibrium spin accumulation and magnetization at the interface. Since the spin polarization of an electric-field-induced non-equilibrium spin accumulation in conventional spin-source materials is restricted to be in the film plane, the ensuing UMR can only respond to the in-plane component of magnetization. However, magnets with perpendicular magnetic anisotropy are highly desired for magnetic memory and spin-logic devices, whereas the electrical read-out of perpendicular magnetic anisotropy magnets through UMR is critically missing. Here, in this study, we report the discovery of an unconventional UMR in the heterostructures of a topological semimetal (WTe 2 ) and a perpendicular magnetic anisotropy ferromagnetic insulator (Cr 2 Ge 2 Te 6 ), which allows to electrically read the up and down magnetic states of the Cr 2 Ge 2 Te 6 layer through longitudinal resistance measurements.
The ability of gamma-TiAl to withstand potential foreign or domestic object damage is a technical risk to the implementation of gamma-TiAl in low pressure turbine (LPT) blade applications. In the present study, the impact resistance of TiAl alloy ABB-2 was determined and compared to the impact resistance of Ti(48)Al(2)Nb(2)Cr. Specimens were impacted with four different impact conditions with impact energies ranging from 0.22 to 6.09 J. After impacting, the impact damage was characterized by crack lengths on both the front and backside of the impact. Due to the flat nature of gamma-TiAl's S-N (stress vs. cycles to failure) curve, step fatigue tests were used to determine the fatigue strength after impacting. Impact damage increased with increasing impact energy and led to a reduction in the fatigue strength of the alloy. For similar crack lengths, the fatigue strength of impacted ABB-2 was similar to the fatigue strength of impacted Ti(48)Al(2)Nb(2)Cr, even though the tensile properties of the two alloys are significantly different. Similar to Ti(48)Al(2)Nb(2)Cr, ABB-2 showed a classical mean stress dependence on fatigue strength. The fatigue strength of impacted ABB-2 could be accurately predicted using a threshold analysis.
Abstract The field of two-dimensional (2D) ferromagnetism has been proliferating over the past few years, with ongoing interests in basic science and potential applications in spintronic technology. However, a high-resolution spectroscopic study of the 2D ferromagnet is still lacking due to the small size and air sensitivity of the exfoliated nanoflakes. Here, we report a thickness-dependent ferromagnetism in epitaxially grown Cr 2 Te 3 thin films and investigate the evolution of the underlying electronic structure by synergistic angle-resolved photoemission spectroscopy, scanning tunneling microscopy, x-ray absorption spectroscopy, and first-principle calculations. A conspicuous ferromagnetic transition from Stoner to Heisenberg-type is directly observed in the atomically thin limit, indicating that dimensionality is a powerful tuning knob to manipulate the novel properties of 2D magnetism. Monolayer Cr 2 Te 3 retains robust ferromagnetism, but with a suppressed Curie temperature, due to the drastic drop in the density of states near the Fermi level. Our results establish atomically thin Cr 2 Te 3 as an excellent platform to explore the dual nature of localized and itinerant ferromagnetism in 2D magnets.
Here, we carried out a comprehensive study of the structural, electrical transport, thermal, and thermodynamic properties in ferrimagnetic Mn 3 Si 2 Te 6 single crystals. Mn and Te K -edge x-ray absorption spectroscopy and synchrotron powder x-ray diffraction were measured to provide information on the local atomic environment and the average crystal structure. The dc and ac magnetic susceptibility measurements indicate a second-order paramagnetic to ferrimagnetic transition at T c ~ 74 K, which is further confirmed by the specific heat measurement. Mn 3 Si 2 Te 6 exhibits semiconducting behavior along with a large negative magnetoresistance of -87% at T c and a relatively high value of thermopower up to ~10 mV/K at 5 K. Besides the rapidly increasing resistivity ρ(T) and thermopower S(T) below 20 K, the large discrepancy between the activation energy for resistivity E ρ and thermopower E S above 20 K indicates the polaronic transport mechanism. Furthermore, the thermal conductivity κ(T) of Mn 3 Si 2 Te 6 is notably rather low, comparable to Cr 2 Si 2 Te 6 , and is strongly suppressed in the magnetic field across T c , indicating the presence of strong spin-lattice coupling, also similar with Cr 2 Si 2 Te 6 .
Here, by using angle-resolved photoemission spectroscopy, we showed that Bi 2-x Cr x Se 3 single crystals have a distinctly well-defined band structure with a large bulk band gap and undistorted topological surface states. These spectral features are unlike their thin film forms in which a large nonmagnetic gap with a distorted band structure was reported. We further provide laser-based high resolution photoemission data which reveal a Dirac point gap even in the pristine sample. The gap becomes more pronounced with Cr doping into the bulk of Bi 2 Se 3 . These observations show that the Dirac point can be modified by the magnetic impurities as well as the light source.
This report highlights accident-tolerant fuel (ATF) code assessment activities performed under Project NRCHQ- 60-17-T-0017, Lattice Physics Enhancements and Assessment. ATF covers a broad range of advanced fuel and clad designs for light water reactors (LWRs) to enhance performance under several accident conditions. Several ATF concepts are anticipated to be deployed as lead test rods (LTRs) or lead test assemblies (LTAs) within the next five years. The purpose of this work is to assess the predictive capabilities of NRC neutronics codes that underpin various licensing calculations. ATF designs use different fuel and clad materials compared to standard UO 2 fuel and zirconium-alloy claddings (hereafter UO 2 -Zry). These new materials and geometrical designs need to be assessed to quantify the impact of nuclear data uncertainties on quantities of interest (QOIs) in licensing calculations and the impact of modeling approximations which may be valid for UO 2 -Zry but not for ATF. This report outlines a systematic approach for ATF neutronics code assessment which includes sensitivity and uncertainty (S/U) analysis of nuclear data, identification of experimental benchmark and gaps for code validation, investigation of modeling approximations, and code-to-code comparisons of calculated QOIs against high-fidelity reference continuous energy (CE) Monte Carlo (MC) calculations. This report focuses on the assessment of the SCALE/Polaris lattice physics code for reactor safety analysis. Polaris lattice physics calculations generate few group (FG) cross sections for PARCS full-core calculations. (Full-core analysis, spent fuel analysis, and severe accident analysis will be performed in future work.) The selected ATF concepts for this report include Cr 2 O 3 and Al 2 O 3 -Cr 2 O 3 -doped UO 2 fuel, U 3 Si 2 fuel, FeCrAl cladding, SiC cladding, and Cr-coated cladding.
UO 2 doped with parts per million CR 2 O 3 powder is considered a potential near term accident tolerant fuel candidate. Here, the results of decades of industry and academic research into Cr-doped UO 2 are analyzed and their shortcomings are critiqued. Focusing on the incorporation mechanisms of Cr into the fuel matrix, we explore a mechanistic understanding of the characteristic properties of Cr-doped UO 2 , notably, enhanced fission gas retention attributed to enlarged grain sizes following sintering, along with marginal improvements in the thermophysical properties. The findings of recent X-ray Adsorption Near Edge Spectroscopy studies were compared and put into conversation with historic data regarding the incorporation of Cr in UO 2 . On the basis of defect mechanisms, the case is made for the substitutional incorporation of Cr governing the lattice solubility but not the enhanced U diffusivity. Instead, Cr/CR 2 O 3 redox chemistry in a well-defined oxygen potential explains the differences in the U diffusivity and O/M ratio. The primary mechanism of doping enhanced grain growth is found to be liquid assisted sintering due to a CRO (1) eutectic phase at the grain boundaries. The role of inhomogeneities in Cr concentration in UO 2 at various length scales across the materials microstructure is highlighted and connected to promising experimental and modeling work to fill in the gaps in the current understanding of Cr-doped UO 2 . The review considers both the open scientific questions and engineering applications to illustrate the deep connections between the practice and theory in the design of accident tolerant nuclear fuels. In conclusion, the review ends with an outline of future works that combine meticulous irradiation studies and high resolution experiments with next generation modeling and simulations techniques empowered by machine learning advances to accelerate the fabrication and adoption of Cr-doped UO 2 light water reactors.
Trace metal contaminations in natural waters, wetlands, and wastewaters pose serious threats to aquatic ecosystems—mainly via targeting microalgae. In this work, we investigated the effects of toxic amounts of chromium and cadmium ions on the structure and function of the photosynthetic machinery of Chlorella variabilis cells. To halt the propagation of cells, we used high concentrations of Cd and Cr, 50–50 mg L –1 , in the forms of CdCl 2 x 2.5 H 2 O and K 2 Cr 2 O 7 , respectively. Both treatments led to similar, about 50% gradual diminishment of the chlorophyll contents of the cells in 48 h, which was, however, accompanied by a small (~10%) but statistically significant enrichment (Cd) and loss (Cr) of ß-carotene. Both Cd and Cr inhibited the activity of photosystem II (PSII)—but with more severe inhibitions with Cr. On the contrary, the PsbA (D1) protein of PSII and the PsbO protein of the oxygen-evolving complex were retained more in Cr-treated cells than in the presence of Cd. These data and the higher susceptibility of P700 redox transients in Cr-treated cells suggest that, unlike with Cd, PSII is not the main target in the photochemical apparatus. These differences at the level of photochemistry also brought about dissimilarities at higher levels of the structural complexity of the photosynthetic apparatus. Circular dichroism (CD) spectroscopy measurements revealed moderate perturbations in the macro-organization of the protein complexes—with more pronounced decline in Cd-treated cells than in the cells with Cr. Also, as reflected by transmission electron microscopy and small-angle neutron scattering, the thylakoid membranes suffered shrinking and were largely fragmented in Cd-treated cells, whereas no changes could be discerned with Cr. The preservation of integrity of membranes in Cr-treated cells was most probably aided by high proportion of the de-epoxidized xanthophylls, which were absent with Cd. It can thus be concluded that beside strong similarities of the toxic effects of Cr and Cd, the response of the photosynthetic machinery of C. variabilis to these two trace metal ions substantially differ from each other—strongly suggesting different inhibitory and protective mechanisms following the primary toxic events.
Bi14CrO24 crystallizes in the triclinic P1 space group. The structure is three-dimensional. Cr6+ is bonded to four O2- atoms to form CrO4 tetrahedra that share a cornercorner with one BiO7 pentagonal bipyramid. There are a spread of Cr–O bond distances ranging from 1.66–1.68 Å. There are fourteen inequivalent Bi3+ sites. In the first Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.17–2.94 Å. In the second Bi3+ site, Bi3+ is bonded to five O2- atoms to form distorted corner-sharing BiO5 square pyramids. There are a spread of Bi–O bond distances ranging from 2.13–2.64 Å. In the third Bi3+ site, Bi3+ is bonded in a distorted body-centered cubic geometry to eight O2- atoms. There are a spread of Bi–O bond distances ranging from 2.33–2.83 Å. In the fourth Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.15–3.08 Å. In the fifth Bi3+ site, Bi3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Bi–O bond distances ranging from 2.26–3.09 Å. In the sixth Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.14–2.98 Å. In the seventh Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.14–3.06 Å. In the eighth Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.24–2.84 Å. In the ninth Bi3+ site, Bi3+ is bonded in a 5-coordinate geometry to seven O2- atoms. There are a spread of Bi–O bond distances ranging from 2.15–3.09 Å. In the tenth Bi3+ site, Bi3+ is bonded in a distorted body-centered cubic geometry to eight O2- atoms. There are a spread of Bi–O bond distances ranging from 2.33–2.85 Å. In the eleventh Bi3+ site, Bi3+ is bonded to seven O2- atoms to form distorted BiO7 pentagonal bipyramids that share a cornercorner with one BiO5 square pyramid and a cornercorner with one CrO4 tetrahedra. There are a spread of Bi–O bond distances ranging from 2.27–2.82 Å. In the twelfth Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.15–2.88 Å. In the thirteenth Bi3+ site, Bi3+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.13–2.70 Å. In the fourteenth Bi3+ site, Bi3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Bi–O bond distances ranging from 2.28–2.97 Å. There are twenty-four inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one Cr6+ and two Bi3+ atoms. In the second O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the third O2- site, O2- is bonded to four Bi3+ atoms to form a mixture of corner and edge-sharing OBi4 tetrahedra. In the fourth O2- site, O2- is bonded to four Bi3+ atoms to form a mixture of corner and edge-sharing OBi4 tetrahedra. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the seventh O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the eighth O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the ninth O2- site, O2- is bonded to four Bi3+ atoms to form a mixture of corner and edge-sharing OBi4 tetrahedra. In the tenth O2- site, O2- is bonded to four Bi3+ atoms to form a mixture of corner and edge-sharing OBi4 tetrahedra. In the eleventh O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the twelfth O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the thirteenth O2- site, O2- is bonded to four Bi3+ atoms to form a mixture of corner and edge-sharing OBi4 tetrahedra. In the fourteenth O2- site, O2- is bonded to four Bi3+ atoms to form a mixture of corner and edge-sharing OBi4 tetrahedra. In the fifteenth O2- site, O2- is bonded in a distorted single-bond geometry to one Cr6+ and two Bi3+ atoms. In the sixteenth O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the seventeenth O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the eighteenth O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the nineteenth O2- site, O2- is bonded in a single-bond geometry to one Cr6+ and four Bi3+ atoms. In the twentieth O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the twenty-first O2- site, O2- is bonded to four Bi3+ atoms to form a mixture of corner and edge-sharing OBi4 tetrahedra. In the twenty-second O2- site, O2- is bonded to four Bi3+ atoms to form a mixture of corner and edge-sharing OBi4 tetrahedra. In the twenty-third O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the twenty-fourth O2- site, O2- is bonded in a single-bond geometry to one Cr6+ and two Bi3+ atoms.
CrO2Cl2 is Silicon tetrafluoride-derived structured and crystallizes in the monoclinic P2_1 space group. The structure is zero-dimensional and consists of two CrO2Cl2 clusters. Cr6+ is bonded in a tetrahedral geometry to two O2- and two Cl1- atoms. Both Cr–O bond lengths are 1.59 Å. There are one shorter (2.12 Å) and one longer (2.13 Å) Cr–Cl bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one Cr6+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to one Cr6+ atom. There are two inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Cr6+ atom. In the second Cl1- site, Cl1- is bonded in a single-bond geometry to one Cr6+ atom.
As an alternative fuel form, the annular metallic fuel design eliminates the liquid sodium bond between the fuel and the cladding, providing back-end fuel cycle and other benefits. The fuel-cladding chemical interaction (FCCI) of annular fuel also presents new features. In this work, state-of-the-art electron microscopy and spectroscopy techniques were used to study the FCCI of a prototype annular U-10wt%Zr (U-10Zr) fuel with ferritic/martensitic HT-9 cladding irradiated to 3.3% fission per initial heavy atom. Compared with sodium-bonded solid fuels, negligible amounts of lanthanides were found in the FCCI layer in the investigated helium-bonded annular fuel. Instead, most lanthanides were retained in the newly formed UZr 2 phase in the fuel center region. The interdiffusion of iron and uranium resulted in tetragonal ( U ,Zr) 6 Fe phase (space group I4/mcm) and cubic ( U ,Zr)( Fe ,Cr) 2 phase (space group Fd 3 ¯ m). The ( U ,Zr)( Fe ,Cr) 2 phase contains a high density of voids and intergranular uranium monocarbides of NaCl-type crystal structure (space group Fm 3 ¯ m). At the interdiffusion zone and inner cladding interface, a porous lamellar structure composed of alternating Cr-rich layers and U-rich layers was observed. Next to the lamellar region, the unexpected phase transformation from body-centered cubic ferrite (α-Fe) to tetragonal binary Fe-Cr σ phase (space group P4 2 /mnm) occurred, and tetragonal Fe-Cr-U-Si phase (space group I4/mmm) was identified. Due to the diffusion of carbon into the interdiffusion zone, carbon depletion inside the HT-9 led to the disappearance of the martensite lath structure, and intergranular U-rich carbides formed as a result of the diffusion of uranium into the cladding. These detailed new findings reveal the unique features of the FCCI behavior of annular U-Zr fuels, which could be a promising alternative fuel form for high burnup fast reactor applications.
Understanding the interfacial evolution of alloys in molten salt with different amounts of water (H 2 O) and oxygen (O 2 ) impurities is significant for applications in many fields, including concentrated solar power, molten salt reactors, and applications in pyrochemical reprocessing and electrorefining. Additionally, the impurity-driven corrosion mechanisms that lead to various morphological and chemical evolution characteristics at the interfaces of structural alloys and molten salts are not fully understood. In the present work, the three-dimensional (3D) morphological evolution of Ni-20Cr microwires in LiCl-KCl was studied at 500 °C under different moisture and oxygen conditions using in situ synchrotron transmission X-ray microscopy (TXM) and scanning transmission electron microscopy (STEM) techniques. No significant morphological changes were observed in Ni-20Cr microwires under vacuum conditions. However, the wires exhibited distinct morphological evolutions when exposed to molten salt containing H 2 O alone, as well as when both H 2 O and O 2 were present. Furthermore, Cr 2 O 3 precipitates were observed in the molten salt during corrosion with only H 2 O present, while Cr 6+ species were identified in the salt when O 2 was added. Further, these findings are crucial for understanding the corrosion mechanisms of molten salt with different amounts of H 2 O and O 2 contamination, providing insights for developing corrosion mitigation methods and improving the stability of containment alloys in molten salt applications.
A computational thermodynamics approach has been employed to design CoCrFeMnNi-based medium- and high-entropy alloys (M/HEAs) with systematically varied compositions (Co(( 80-X )/ 2 )Cr(( 80-X )/ 2 )Fe X Mn 10 Ni 10 with x = 30, 40, and 50 at.%) and phase stability. Since the formation of sigma phase, usually brittle and undesirable, is a common concern, when this class of alloys is subjected to elevated temperatures (600–1000 °C), predicting its formation becomes essential. Thus, its formation and the phase equilibria were studied using the CALPHAD method, and two empirical methods, namely, valence electron concentration (VEC) and paired sigma-forming element (PSFE). Isothermal aging treatments at 900–1100 °C for 20 h were performed, since CALPHAD and VEC/PSFE predictions diverged. Both prediction methods were compared with experimental characterization by a combination of scanning electron microscopy and high-energy synchrotron X-ray diffraction. In conclusion, the predictions from the VEC/PSFE and CALPHAD calculations (depending on the database used) were shown to be quite accurate.
Combining single-molecule magnets (SMMs) and emergent two-dimensional substrates such as graphene may lead to device configurations that are promising for spintronics and quantum computing. Yet, to fully consider the unique features of SMMs anchored to two-dimensional substrates, the choice of ligand attachments, which could affect the magnetic and electronic properties, is critical. In this work, we focus on hybrid junctions comprising CVD-grown graphene and [Mn 12 O 12 (O 2 CR) 16 (H 2 O) 4 ]( R = CH 3 , CHCl 2 ) SMMs with different ligands. We find that [Mn 12 O 12 (O 2 CCH 3 ) 16 (H 2 O) 4 ] SMMs barely change the graphene’s conductivity, while [Mn 12 O 12 (O 2 CCHCl 2 ) 16 (H 2 O) 4 ] SMMs with more electronegative ligands, by means of charge transfer, remarkably modify the electronic transport in graphene as revealed by gate-voltage dependent magnetotransport measurements.
Here, in this work, the structural, optical, and electronic properties of rare-earth perovskites of the general formula R CrO 3 , where R represents the rare-earth Gd, Tb, Dy, Ho, Er, and Tm, have been studied in detail. These compounds were synthesized through a facile citrate route. X-ray diffraction, Raman spectroscopy, and UV-Visible spectroscopy were utilized to reveal the structural evolutions in R CrO 3 . The lattice parameters, Cr 3+ –O 2 –Cr 3+ bond angle, and CrO 6 octahedral distortions were found to strongly depend on the ionic radii of R . First-principles calculations based on density-functional theory within the generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof (PBE) and strongly constrained and appropriately normed (SCAN) meta-GGA were also employed to calculate the structural and electronic properties of R CrO 3 . The ground-state energy, lattice constants, electronic structures, and density of states of R CrO 3 were calculated. These provide some insights into the electronic characteristics of the R CrO 3 compounds. The calculated values of lattice parameters and band gaps with Hubbard U correction (SCAN+ U ) agree well with values measured experimentally and show more accuracy in predicting the ground-state crystal structure and band structure compared to PBE+ U approximation. The band gap of R CrO 3 is found to be independent of the ionic radii of R from both experiments and calculations.
Abstract A literature compilation of 1136 low‐Ca pyroxene compositions from chondrules from 12 primitive type 2–3 carbonaceous, ordinary and enstatite chondrite groups define unique regions on an Al 2 O 3 and Cr 2 O 3 diagram when compared to low‐Ca pyroxenes from equilibrated type 4‐6 chondrites. Measured compositions of 100 low‐Ca pyroxenes from comet Wild 2 and a giant cluster IDP of probable cometary origin are similar to each other and fall in the type 2–3 chondrite chondrule region suggesting that most of the pyroxenes likely formed in the solar nebula like conventional chondrules. The data imply that most low Ca‐pyroxenes from comet Wild 2 and the giant cluster IDP formed from igneous crystallization processes and did not experience significant thermal metamorphism, indicating that the low‐Ca pyroxenes were unlikely incorporated into large parent bodies prior to accretion in their respective comet bodies. An intriguing group of nine low‐Ca pyroxenes from comet Wild 2 with low Cr and Al that fall where type 4–6 chondrites are located are interpreted as products of condensation. The compositional data combined with previously measured oxygen isotopes on 17 low‐Ca pyroxenes support earlier conclusions that comet samples have links with carbonaceous, ordinary, and possibly enstatite chondrite groups. Our results provide additional evidence that comets accreted materials from multiple chondrule reservoirs throughout the solar nebula.