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DOE OSTI2019

Morphology-dependent stability of complex metal hydrides and their intermediates using first-principles calculations

Complex light metal hydrides are promising candidates for efficient, compact solid-state hydrogen storage. (De)hydrogenation of these materials often proceeds via multiple reaction intermediates, the energetics of which determine reversibility and kinetics. At the solid-state reaction front, molecular-level chemistry eventually drives the formation of bulk product phases. Therefore, a better understanding of realistic (de)hydrogenation behavior requires considering possible reaction products along all stages of morphological evolution, from molecular to bulk crystalline. Here, we use first-principles calculations to explore the interplay between intermediate morphology and reaction pathways. Employing representative complex metal hydride systems, we investigate the relative energetics of three distinct morphological stages that can be expressed by intermediates during solid-state reactions: i) dispersed molecules; ii) clustered molecular chains; and iii) condensed-phase crystals. Our results verify that the effective reaction energy landscape strongly depends on the morphological features and associated chemical environment, offering a possible explanation for observed discrepancies between X-ray diffraction and nuclear magnetic resonance measurements. Our theoretical understanding also provides physical and chemical insight into phase nucleation kinetics upon (de)hydrogenation of complex metal hydrides.

08 HYDROGEN↗

DOE OSTI2022

Structural Flexibility of Metal Chelate Complexes and Its Relation to Supramolecular Chemistry

In this study, crystal structures of metal chelate and related complexes in the Cambridge Structural Database have been analyzed, with respect to their use as components in supramolecular metal-organic compounds. In β-diketonate complexes, the distribution of angles between ligands is relatively broad; other ligands, such as 2,2'-bipyridine, yield significantly narrower distributions. According to the principle of structure correlation, these distributions reflect the ease of distorting the various families of complexes. A comparison through density functional theory calculations also indicates that angular distortions require significantly less energy for M(β-diketonate) 3 than for M(2,2'-bipyridine) 3 . The differences are likely to affect the construction of supramolecular systems from different combinations of metals and ligands, including the likelihood that the desired structures will be obtained.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Complexation of Plutonium(IV) with trans-1,2-Diaminocyclohexane-N,N,N',N'-tetraacetic Acid (CDTA) in Acidic Solution

Understanding the interaction of Pu(IV) with complexing agents present in the nuclear fuel cycle is important for predicting the performance of used nuclear fuel separations. The complexation of Pu(IV) with trans -1,2-diaminocyclohexane-N,N,N’,N’-tetraacetic acid (CDTA) was studied in acidic solutions of 0.10 0.50 mol∙L -1 HClO 4 with 1.00 mol∙L -1 (Na,H)ClO 4 total ionic strength by a liquid–liquid extraction method using tracer quantities of 238 Pu. The acid dissociation constants of CDTA and the autoprotolysis constant of water were determined via potentiometric titrations in 0.10–2.00 mol∙L -1 NaClO 4 and 25.0 ± 0.1 °C. The variation of the dissociation constants with ionic strength was modeled with the Specific ion Interaction Theory (SIT) and the associated SIT parameters were obtained. The thermodynamic dissociation 23 constants at zero ionic strength for water and CDTA were determined from this analysis as PK$^o_w$ = 14.00 ± 0.03, PK$^o_{a2}$ = 1.52 ± 0.04, PK$^o_{a3}$ = 2.78 ± 0.05, PK$^o_{a4}$ = 4.17 ± 0.04, PK$^o_{a5}$ = 6.75 ± 0.02, and PK$^o_{a6}$ = 10.64 ± 0.04 at 25.0 ± 0.1 °C. The results of the liquid–liquid extraction experiments indicated the formation of a 1:0:1 complex, PuCDTA o , and the presence of additional protonated species, Pu(HCDTA) + and Pu(H 2 CDTA )2+ , at these acidities. The corresponding stability constants in 1.00 mol·L -1 (Na,H)ClO 4 and 23 ± 1 °C were determined to be log 10 β 101 =24.2 ± 0.3, log 10 β 111 =25.4 ± 0.2, and log 10 β 121 = 25.8 ± 0.1.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2018

Spin crossover in homo- and heteroligand iron(II) complexes with tris(pyrazol-1-yl)methane derivatives

The studies concerning coordination compounds of various salts of iron(II) with tris(pyrazol-1-yl)methane derivatives (HC(pz){sub 3}) are discussed. The results of a number of studies on the synthesis and investigation of the homo- and heteroligand iron(II) complexes with tris(3,5- dimethylpyrazol-1-yl)methane (HC(3,5-Me{sub 2}pz){sub 3}) are considered. The study of the temperature dependence μ{sub eff} (T) showed that the spin crossover (SCO) {sup 1}A{sub 1}↔{sup 5}T{sub 2} observed in a series of the compounds discussed is accompanied by thermochromism (color change pink (purple) ↔ colorless). Specific features of the SCO and their dependence on the outer-sphere anion in the iron(II) complexes are discussed. The data of the recently published work devoted to the synthesis of the iron(II) complexes with three N-substituted HC(pz){sub 3} derivatives (general formula {sup x}L, where x = H, CH{sub 2}C{sub 6}H{sub 5} (Bn) and p-SO{sub 3}C{sub 6}H{sub 4}CH{sub 3} (Ts)) are considered.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

Quantum chemical study of formation of Cu{sup II}–Y{sup III} metallamacrocyclic complexes based on glycinehydroximate ligands

The process of solution-phase formation of the Cu{sup II}–Y{sup III} 15-metallacrown-5 complexes bearing the glycinehydroximate ligands has been for the first time investigated by methods of quantum chemistry. The DFT modeling at the B3LYP/DGDZVP (PCM) level was carried out for mono-, bi-, and tri-nuclear copper(II) complexes and also for heteronuclear Cu{sup II}–Y{sup III} derivatives as the metallamacrocycle precursors. The dependence of relative stability of these complexes on the Cu{sup II} and Y{sup III} coordination surroundings and also on the mutual positions of ligands was found. The structural (variations of interatomic distances and valence angles), electronic (changes in the atomic charges and electron density), and thermodynamical (enthalpies and Gibbs free energies) regularities of 15-metallacrown-5 formation were revealed. The key role of Y{sup III} cation was established for the process of formation of the polynuclear metallamacrocyclic compound (15-metallacrown-5).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

Reactivity of an aluminum hydride complex with a redox-active diimine ligand

The reaction of the hydride [(dpp-bian)Al(H)Cl] (1) containing the 1,2-bis[(2,6-diisopropylphenyl) imino]acenaphthene (dpp-bian) radical anion with MeLi affords the compound [(dpp-bian)Al(H)Me] (2). The reaction of complex 1 with two equivalents of PhC≡CNa involves the replacement of chlorine along with oxidative substitution of hydrogen accompanied by the reduction of dpp-bian to the dianion to form the compound [(dpp-bian)Al(C≡CPh){sub 2}Na(Et{sub 2}O){sub 2}] ({sn3}). This reaction gives the complex [{dpp-bian(H)}Al(C≡CPh){sub 3}Na(Et{sub 2}O){sub 2}] (4) as the second product, which is apparently generated in the reaction of compound 3 with PhC≡CH. The reaction of compound 1 with Cp*Na (Cp* is pentamethylcyclopentadiene) in dimethoxyethane is also accompanied by the reduction of redox-active dpp-bian to the dianion, giving the complex [(dpp-bian)Al(H)Cl][Na(DME){sub 3}] (5). Diamagnetic derivatives 3–5 were characterized by {sup 1}H NMR spectroscopy; paramagnetic compound 2, by EPR spectroscopy. The molecular structures of compounds 2–5 were determined by X-ray diffraction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Mononuclear gallium complexes with the redox-active dmp-bian ligand (dmp-bian is 1,2-bis[(2,6-dimethylphenyl)imino]acenaphthene): synthesis and reactions with alkynes

The direct reduction of 1,2-bis[(2,6-dimethylphenyl)imino]acenaphthene (dmp-bian (1)) with gallium metal in toluene affords the solvent-free bis-ligand complex [(dmp-bian){sub 2}Ga] (2), in which two diimine ligands are in different oxidation states (radical-anionic and dianionic). The addition of phenylacethylene to the Ga–N–C moiety of the dianionic ligand of compound 2 gives the complex [(dmp-bian)Ga(HC=CPh)(dmp-bian)] (3), in which new Ga–C and C–C bonds are formed. The reaction of 2 with hex-1-yne produces the gallium dialkynyl complex [(dmp-bian)Ga(C≡C–Bu){sub 2}] (4), with the metal atom bonded to the dmp-bian radical anion. Paramagnetic compounds 2–4 were characterized by ESR spectroscopy and X-ray diffraction. The known compound dmp-bian was structurally characterized for the first time.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Mapping tree height in complex terrain of northern China using ultra-high-resolution images

Tree height is a key parameter for estimating forest biomass and carbon sequestration. In recent years, notable progress has been made in mapping tree height using satellite imagery. However, existing tree height products show low accuracy in mountainous and complex terrains, and few studies typically addressed tree height estimations in mountain areas. This study examines the Mentougou district of Beijing, China, characterized by complex terrain and mountainous landscapes. We analyzed two methods for estimating tree height: one using only spectral features and another combining spectral features with topographic factors (elevation, slope, aspect). We used 3-m resolution PlanetScope 8-band multispectral imagery, with 710 field-measured individual tree heights averaged to obtain 471 pixel-level tree height values as ground-truth, to develop tree height prediction models using eXtreme Gradient Boosting (XGBoost), Random Forest (RF), and Gradient Boosting Machine (GBM) models. The results show that the XGBoost model consistently presented the highest accuracy for both methods evaluated. Specifically, the XGBoost model that combined spectral data with elevation and slope variables with an R² of 0.75 and an RMSE of 2.69 m. Using the XGBoost model, we generated the tree height map for the Mentougou area at 3 m resolution, showing tree heights ranging from 0.5 to 30.4 m, and the model’s prediction error standard deviations ranged from 2.50 to 4.71 m, indicating reliable performance across varied terrain. Additionally, we compared and evaluated the global tree height products, identifying limitations in the accuracy within complex terrains. This study demonstrates the potential for accurately predicting tree heights by combining high-resolution multispectral satellites with a terrain factor modeling approach.

Complex terrain↗

DOE OSTI2018

Electrogenic reactions in Mn-depleted photosystem II core particles in the presence of synthetic binuclear Mn complexes

An electrometrical technique was used to investigate electron transfer between synthetic binuclear manganese (Mn) complexes, designated M − 2 and M − 3, and the redox-active neutral tyrosine radical (Y{sub Z}{sup • }) in proteoliposomes containing Mn-depleted photosystem II (PS II) core particles in response to single laser flashes. In the absence of Mn-containing compounds, the observed flash-induced membrane potential (ΔΨ) decay was mainly due to charge recombination between the reduced primary quinone acceptor Q{sub A}{sup −} and the oxidized Y{sub Z}{sup • }. More significant slowing down of the ΔΨ decay in the presence of lower concentrations of M − 2 and M − 3 associated with electron donation from Mn in the Mn-binding site to Y{sub Z}{sup • }indicates that these synthetic compounds are more effective electron donors than MnCl{sub 2}. The exponential fitting of the kinetics of additional electrogenic components of ΔΨ rise in the presence of Mn-containing compounds revealed the following relative amplitudes (A) and lifetimes (τ): for MnCl{sub 2} - A∼ 3.5, τ∼150 μs, for M − 2 - A∼5%, τ∼1.4 ms, and for M − 3 - A∼5.5%, τ∼150 μs. This suggests that the efficiency of the manganese complexes in electron donation depends on the chemical nature of ligands. The experiments with EDTA-treated samples indicated that the ligands for M − 2 and M − 3 are required for their tight binding with the PS II reaction center. The obtained results demonstrate the importance of understanding the molecular mechanism(s) of flash-induced electrogenic reduction of the tyrosine radical Y{sub Z}{sup • }by synthetic Mn complexes capable of splitting water into oxygen and reducing equivalents.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2023

Mechanisms of Zn removal from water by amorphous geopolymer: Molecular-level insights from X-ray absorption spectroscopy, isotope fractionation, and surface complexation modeling

Porous geopolymers have attracted widespread attention as promising heavy metal adsorbents that can be synthesized from aluminosilicate solid wastes. However, the precise microstructural evidence for adsorbed heavy metals on geopolymers remains unclear due to the insensitivity of conventional characterization techniques on minerals with amorphous structure and surface disorder. Batch adsorption and column experiments coupled with X-ray absorption spectroscopy (XAS), Zn stable isotope, and surface complexation model (SCM) were employed to reveal the Zn removal mechanisms with coal fly ash porous geopolymer (CFAPG) at a molecular scale. The macroscopic kinetic and isothermal adsorption of Zn on CFAPG were well described by the pseudo-second-order model and Bi_Langmuir equation, respectively, indicating the presence of abundant heterogeneous active sites on the CFAPG surface. Further, two types of active sites on the CFAPG surface were identified by XAS coupled with Zn isotopes in batch experiments at pH <= 6.0: one is pH-dependent and associated with tetrahedral zinc coordi-nation, and the other is pH-insensitive and associated with octahedral zinc coordination; these sites were confirmed by the bidentate SCM as the variable charge site (surface complexation, >S-OH) and the permanent negative charge site (cation exchange, >X - ), respectively. Furthermore, the important contribution of surface co -precipitation besides surface complexation and cation exchange to the Zn adsorption on CFAPG was identified by XAS coupled with SCM in a flow-through column experiment at pH >6.0. These investigations provide a systemic understanding of the Zn adsorption mechanisms on CFAPG and an SCM reference for the application and prediction of geopolymers in heavy metal-contaminated water remediations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Roles of surface Mn(III) and MgOH + /CaOH + complexation in photochemically assisted Mn 2+ oxidation and Todorokite formation

Todorokite, a Mn oxide phase commonly found in seafloor Mn nodules, is one of the most abundant Mn oxides in nature and has wide applications in environmental engineering, including heavy metal remediation, contaminant adsorption for water purification, and catalysis for organic pollutant degradation. However, traditional abiotic formation of todorokite reported to date typically requires high temperature, pressure, and pH outside circumneutral conditions, or involves several days of phase transformations from precursor phases. In this study, we demonstrate rapid todorokite formation within 6 h via photochemically assisted oxidation of Mn 2+ (aq) in the presence of Mg 2+ or Ca 2+ , notably at ambient temperature and pressure. The concentrations of aqueous MgOH + and CaOH + , as well as the pH (initial 9 or 6), had significant collective influences on the crystalline phases of the formed Mn oxide solids. The proportions of the Mn oxidation states (IV, III, and II) and the extent of Mn(III) surface complexation with MgOH + or CaOH + controlled the crystalline phases (todorokite, feitknechtite, and birnessite) and the extent of cation incorporation into the resulting Mn oxide solids. Specifically, the oxidation state of Mn influenced the crystallization of different Mn oxide phases, and the formed Mn(III) complexed with MgOH + or CaOH + facilitated the formation of todorokite, along with cation incorporation. X-ray pair distribution function analysis revealed that incorporated Mg species were located at the inside corner sites of the 5 × 3 MnO 6 octahedral tunnel structure of todorokite, suggesting complexation between MgOH + and Mn(III) at the corners of the tunnel. Furthermore, this study provides novel insights into the elusive formation of todorokite and its potential for applications in advanced water treatment and environmental remediation.

Abiotic Mn2+ oxidation↗

DOE OSTI2024

A numerical study of process complexity in permafrost dominated regions

Numerical modeling of permafrost dynamics requires adequate representation of atmospheric and surface processes, a reasonable parameter estimation strategy, and site-specific model development. The three main research objectives of the study are: (i) to propose a novel methodology that determines the required level of surface process complexity of permafrost models by conducting parameter sensitivity and calibration, (ii) to design and compare three numerical models of increasing surface process complexity, and (iii) to calibrate and validate the numerical models at the Yakou catchment on the Qinghai-Tibet Plateau as an exemplary study site. The calibration was carried out by coupling the Advanced Terrestrial Simulator (numerical model) and PEST (calibration tool). Simulation results showed that (i) A simple numerical model that considers only subsurface processes can simulate active layer development with the same accuracy as other more complex models that include surface processes. (ii) Peat and mineral soil layer permeability, Van Genuchten alpha, and porosity are highly sensitive. (iii) Liquid precipitation aids in increasing the rate of permafrost degradation. (iv) Deposition of snow insulated the subsurface during the thaw initiation period. We have developed and released an integrated code that couples the numerical software ATS to the calibration software PEST. The numerical model can be further used to determine the impacts of climate change on permafrost degradation.

Calibration↗

DOE OSTI2021

Dimensionality effects on multicomponent ionic transport and surface complexation in porous media

Coulombic interactions between charged species in pore water and at surface/solution interfaces are of pivotal importance for multicomponent reactive transport in porous media. In this study, we investigate the impact of domain dimensionality on electrostatically coupled dispersion and surface-solution reactions during transport of acidic plumes and major ions in porous media. Column and quasi two-dimensional flow-through experiments were performed, with identical silica porous media and under the same advection-dominated conditions. Equal mass fluxes of different electrolyte solutions (i.e., HCl - pH ~ 2.8, NaBr - 100 mM, HCl - pH ~ 2.8 plus NaBr - 100 mM) were continuously injected in the 1-D and 2-D experiments and breakthrough curves of pH and major ions were measured at the outlet of the domains. The presence of pronounced ionic strength gradients in the transverse direction in the 2-D setup caused distinct retardation and transport behaviors of protons and major ions which were not observed in the one-dimensional column experiments. Furthermore, in the cases of salt electrolytes injection, considerably enhanced release of H + (>61%) from the quartz surface was observed in the multidimensional system compared to the one-dimensional setup. Reactive transport modeling was performed to reproduce the experimental outcomes and to analyse the coupling between transport processes, based on the Nernst-Planck formulation of diffusive/dispersive fluxes and on surface complexation reactions at the solid-solution interface. Electrostatic interactions between Na + , B – , and H + , and deprotonation of the quartz surface upon the formation of sodium outer-sphere complexes, are the primary controllers of the spatial and temporal features displayed by the pH and major ions measurements. The reactive transport simulations allowed us to interpret the experimental observations, to visualize the distribution and spatio-temporal evolution of dissolved and solid species, to identify a spatially heterogeneous zonation of Coulombic interactions with distinct behavior at the fringe and core of the injected plumes in the multidimensional setup, and to quantify the different components of the Nerst-Planck fluxes of the charged solutes. This study demonstrates that the domain dimensionality directly affects electrostatic interactions between charged aqueous species in the pore water and surface complexation reactions at the solid-solution interface. The non-trivial effects of dimensionality on multicomponent ionic transport result in a significantly different behavior in 1-D and 2-D systems.

58 GEOSCIENCES↗

DOE OSTI2022

High methylation potential of mercury complexed with mixed thiolate ligands by Geobacter sulfurreducens PCA

We report some thiols, such as cysteine (CYS) at moderate concentrations (10–500 µM), can enhance methylmercury (MeHg) formation by Geobacter sulfurreducens PCA, whereas others such as dithiol 2,3-dimercaptopropanesulfonate (DMPS) and 2,3-dimercaptosuccinic acid (DMSA) abolish mercury [Hg(II)] methylation. Little is known, however, about whether Hg(II) methylation could be enhanced or inhibited by the presence of mixed thiol ligands at low concentrations observed in the environment. Surprisingly we found that mixing CYS (1 µM) with DMPS (0.025–0.5 µM) or DMSA (0.025–1 µM) substantially increased MeHg production by 1.5–3.5-fold, compared to the no-thiol control, whereas complexation with a single DMPS, or DMSA, or CYS (1 µM) strongly inhibited Hg(II) methylation. Pre-equilibration between Hg(II) and thiols before the addition of cells was necessary to observe enhanced methylation. Spectroscopic analyses indicated the formation of mixed or heteroleptic coordinated Hg(II)-S 3 /S 4 complexes, which likely facilitated exchange of Hg(II) with cells and its uptake and internal transfer to the HgcAB proteins required for methylation. These results suggest that the effects of thiols on Hg(II) methylation were more complex than previously thought (using a single thiol) and thus underscore the importance of understanding how mixed thiols and their interactions with Hg(II) may ultimately influence MeHg production in the natural environment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

The major trimeric antenna complexes serve as a site for qH-energy dissipation in plants

Plants and algae are faced with a conundrum: harvesting sufficient light to drive their metabolic needs while dissipating light in excess to prevent photodamage, a process known as nonphotochemical quenching. A slowly relaxing form of energy dissipation, termed qH, is critical for plants’ survival under abiotic stress; however, qH location in the photosynthetic membrane is unresolved. Here, we tested whether we could isolate subcomplexes from plants in which qH was induced that would remain in an energy-dissipative state. Interestingly, we found that chlorophyll (Chl) fluorescence lifetimes were decreased by qH in isolated major trimeric antenna complexes, indicating that they serve as a site for qH-energy dissipation and providing a natively quenched complex with physiological relevance to natural conditions. Next, we monitored the changes in thylakoid pigment, protein, and lipid contents of antenna with active or inactive qH but did not detect any evident differences. Finally, we investigated whether specific subunits of the major antenna complexes were required for qH but found that qH was insensitive to trimer composition. Because we previously observed that qH can occur in the absence of specific xanthophylls, and no evident changes in pigments, proteins, or lipids were detected, we tentatively propose that the energy-dissipative state reported here may stem from Chl–Chl excitonic interaction.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2023

Scalable simulation of coupled adsorption and transport of methane in confined complex porous media with density preconditioning

The growing significance of shales and tight formations in the transition to less carbon-intensive and clean energy drives the research endeavor to understand the physics of gas flow within these systems. However, shales are composed of massively heterogeneous physical and chemical features. Most nano-sized pores connect to millimeter-scale fractures, leading to multiscale transport. These nano-scale pore throats demonstrate non-classical flow behavior, such as non-negligible slip velocities and adsorbed gas layers at the boundary. As a result, classical computational fluid dynamics models do not capture the physics. In this work, we develop a coupling scheme for the multiple-relaxation-time (MRT) lattice Boltzmann (LB) method that integrates the Peng-Robinson equation of state into a pseudo-potential interaction model to capture the physics of methane flow in irregular networks of channels that represent nano-scale porous media. We use atomistic simulations to calibrate and validate our model in slit nano-channels. We propose a preconditioning scheme to initialize the coupled transport and adsorption simulation of methane in complex porous media. The results of this implementation of LB agree with Direct Simulation Monte Carlo (DSMC) and Molecular Dynamics (MD) simulations. We then scale up the LB implementation through vectorization and indirect addressing. We parallelize it using Message Passing Interface (MPI) and OpenMP frameworks to simulate transport and adsorption in complex media with a million lattices. Additionally, we analyze the differences between coupled and transport-only simulations in two case studies and show that considering phase behavior, i.e., adsorption, can significantly change the flow behavior. This work constitutes an important step towards bridging the gap between molecular flow and system-scale behavior of complex disordered porous media.

42 ENGINEERING↗

DOE OSTI2025

Energy migration and scintillation kinetics in compositionally complex (Gd 1/4 Y 1/4 Tb 1/4 Lu 1/4 ) 3 Al 5 O 12 :Ce single crystal scintillator

It is well-established that compositional tuning through binary admixture can improve scintillation performance in several materials systems, including Ce-activated garnets. Although recent work on ternary or quaternary cation admixture shows promise, the impact of this increased compositional complexity on thermal stability and carrier-defect dynamics has not been addressed. Here, we investigate a compositionally complex garnet, (Gd 1/4 Y 1/4 Tb 1/4 Lu 1/4 ) 3 Al 5 O 12 :Ce (GYTLAG), grown by the Czochralski method using temperature-dependent photoluminescence (PL), PL decay, and thermoluminescence (TL). PL and PL decay measurements support a thermally activated Tb 3+ -Ce 3+ energy transfer, where Tb 3+ emission dominates below 60 K, but Ce 3+ emission increases from 20-300 K. Thermal quenching of Ce 3+ emission occurs around T 50 = 508 K, with an activation energy of 0.6 eV. TL and wavelength-resolved TL spectra from 20–500 K show that GYTLAG contains similar trap groups to LuAG but with a broader distribution of glow peaks below room temperature, possibly caused by quaternary cation mixing. A combination of dose dependence, partial cleaning and initial rise, and glow curve fitting to a first order continuous Gaussian distribution model are used to understand the contribution of electronic point defects to scintillation decay and afterglow at room temperature. Furthermore, these results inform how increased compositional complexity influences recombination dynamics in garnet scintillators.

Compositionally complex↗

DOE OSTI2026

A simple Rice-Ashby ductile–brittle transition temperature (DBTT) model based on dislocation mobility for body-centered cubic complex concentrated alloys

A simple Rice-Ashby type model for ductile–brittle transition temperature (DBTT) of body-centered cubic (bcc) complex concentrated alloys (structures) is presented. The effect of accumulation of dislocation density on DBTT is also analyzed. The model results are compared with experimental yield stress vs. temperature data for four complex concentrated alloys: Nb 45 Ta 25 Ti 15 Hf 15 (NTTH), MoNbTaW, HfNbTaTiZr, NbTiZr and two pure bcc metals, Fe and W. It is shown that the DBTT behavior of these alloys and pure metals are in agreement with the simple ductility model presented in this manuscript. The DBTT model presented in this manuscript along with yield strength models for bcc complex concentrated alloys described in the literature should serve as a useful guide for designing such alloys with good high temperature strength and significant room temperature ductility.

Crack tip processes↗