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DOE OSTI2020

Materials Data on CdPb3 by Materials Project

CdPb3 is Uranium Silicide-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Cd is bonded to twelve Pb atoms to form CdPb12 cuboctahedra that share corners with four equivalent CdPb12 cuboctahedra, edges with eight equivalent CdPb12 cuboctahedra, edges with sixteen equivalent PbCd4Pb8 cuboctahedra, faces with four equivalent CdPb12 cuboctahedra, and faces with eight equivalent PbCd4Pb8 cuboctahedra. There are four shorter (3.40 Å) and eight longer (3.55 Å) Cd–Pb bond lengths. There are two inequivalent Pb sites. In the first Pb site, Pb is bonded to four equivalent Cd and eight Pb atoms to form distorted PbCd4Pb8 cuboctahedra that share corners with twelve equivalent PbCd4Pb8 cuboctahedra, edges with eight equivalent CdPb12 cuboctahedra, edges with eight equivalent PbCd4Pb8 cuboctahedra, faces with four equivalent CdPb12 cuboctahedra, and faces with ten equivalent PbCd4Pb8 cuboctahedra. There are four shorter (3.40 Å) and four longer (3.55 Å) Pb–Pb bond lengths. In the second Pb site, Pb is bonded in a square co-planar geometry to four equivalent Cd and eight equivalent Pb atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnCd4S5 by Materials Project

MnCd4S5 is Enargite-like structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. Mn2+ is bonded to four S2- atoms to form MnS4 tetrahedra that share corners with six equivalent MnS4 tetrahedra and corners with six CdS4 tetrahedra. There are one shorter (2.42 Å) and three longer (2.50 Å) Mn–S bond lengths. There are four inequivalent Cd2+ sites. In the first Cd2+ site, Cd2+ is bonded to four S2- atoms to form CdS4 tetrahedra that share corners with three equivalent MnS4 tetrahedra and corners with nine CdS4 tetrahedra. All Cd–S bond lengths are 2.57 Å. In the second Cd2+ site, Cd2+ is bonded to four S2- atoms to form corner-sharing CdS4 tetrahedra. There are one shorter (2.55 Å) and three longer (2.56 Å) Cd–S bond lengths. In the third Cd2+ site, Cd2+ is bonded to four S2- atoms to form corner-sharing CdS4 tetrahedra. There are three shorter (2.55 Å) and one longer (2.56 Å) Cd–S bond lengths. In the fourth Cd2+ site, Cd2+ is bonded to four S2- atoms to form CdS4 tetrahedra that share corners with three equivalent MnS4 tetrahedra and corners with nine CdS4 tetrahedra. There are three shorter (2.57 Å) and one longer (2.59 Å) Cd–S bond lengths. There are five inequivalent S2- sites. In the first S2- site, S2- is bonded to four Cd2+ atoms to form corner-sharing SCd4 tetrahedra. In the second S2- site, S2- is bonded to four Cd2+ atoms to form corner-sharing SCd4 tetrahedra. In the third S2- site, S2- is bonded to four Cd2+ atoms to form corner-sharing SCd4 tetrahedra. In the fourth S2- site, S2- is bonded to three equivalent Mn2+ and one Cd2+ atom to form corner-sharing SMn3Cd tetrahedra. In the fifth S2- site, S2- is bonded to one Mn2+ and three equivalent Cd2+ atoms to form corner-sharing SMnCd3 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on RbV3Cd4O12 by Materials Project

RbV3Cd4O12 crystallizes in the monoclinic Cc space group. The structure is three-dimensional. Rb1+ is bonded in a 10-coordinate geometry to ten O2- atoms. There are a spread of Rb–O bond distances ranging from 2.80–3.44 Å. There are three inequivalent V5+ sites. In the first V5+ site, V5+ is bonded to four O2- atoms to form VO4 tetrahedra that share corners with four CdO6 octahedra and corners with two equivalent CdO6 pentagonal pyramids. The corner-sharing octahedra tilt angles range from 53–61°. There are a spread of V–O bond distances ranging from 1.74–1.78 Å. In the second V5+ site, V5+ is bonded to four O2- atoms to form VO4 tetrahedra that share corners with four CdO6 octahedra and corners with two equivalent CdO6 pentagonal pyramids. The corner-sharing octahedra tilt angles range from 40–66°. There are a spread of V–O bond distances ranging from 1.72–1.78 Å. In the third V5+ site, V5+ is bonded to four O2- atoms to form VO4 tetrahedra that share corners with four CdO6 octahedra and corners with two equivalent CdO6 pentagonal pyramids. The corner-sharing octahedra tilt angles range from 39–65°. There are a spread of V–O bond distances ranging from 1.71–1.81 Å. There are four inequivalent Cd2+ sites. In the first Cd2+ site, Cd2+ is bonded to six O2- atoms to form distorted CdO6 pentagonal pyramids that share corners with six VO4 tetrahedra and edges with two CdO6 octahedra. There are a spread of Cd–O bond distances ranging from 2.36–2.41 Å. In the second Cd2+ site, Cd2+ is bonded to six O2- atoms to form CdO6 octahedra that share corners with six VO4 tetrahedra, an edgeedge with one CdO6 octahedra, and an edgeedge with one CdO6 pentagonal pyramid. There are a spread of Cd–O bond distances ranging from 2.27–2.33 Å. In the third Cd2+ site, Cd2+ is bonded to six O2- atoms to form CdO6 octahedra that share corners with six VO4 tetrahedra, an edgeedge with one CdO6 octahedra, and an edgeedge with one CdO6 pentagonal pyramid. There are a spread of Cd–O bond distances ranging from 2.25–2.34 Å. In the fourth Cd2+ site, Cd2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Cd–O bond distances ranging from 2.31–2.92 Å. There are twelve inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Rb1+, one V5+, and one Cd2+ atom. In the second O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent Rb1+, one V5+, and one Cd2+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to one V5+ and three Cd2+ atoms. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one V5+ and two Cd2+ atoms. In the fifth O2- site, O2- is bonded in a 1-coordinate geometry to one Rb1+, one V5+, and two Cd2+ atoms. In the sixth O2- site, O2- is bonded in a 1-coordinate geometry to one Rb1+, one V5+, and two Cd2+ atoms. In the seventh O2- site, O2- is bonded in a 1-coordinate geometry to one Rb1+, one V5+, and two Cd2+ atoms. In the eighth O2- site, O2- is bonded in a 1-coordinate geometry to one Rb1+, one V5+, and two Cd2+ atoms. In the ninth O2- site, O2- is bonded in a 3-coordinate geometry to one V5+ and two Cd2+ atoms. In the tenth O2- site, O2- is bonded in a 4-coordinate geometry to one V5+ and three Cd2+ atoms. In the eleventh O2- site, O2- is bonded in a 1-coordinate geometry to one Rb1+, one V5+, and two Cd2+ atoms. In the twelfth O2- site, O2- is bonded in a 1-coordinate geometry to one Rb1+, one V5+, and two Cd2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cd4As2Br3 by Materials Project

Cd4As2Br3 crystallizes in the cubic Pa-3 space group. The structure is three-dimensional. there are two inequivalent Cd2+ sites. In the first Cd2+ site, Cd2+ is bonded in a rectangular see-saw-like geometry to two As+2.50- and two equivalent Br1- atoms. There are one shorter (2.60 Å) and one longer (2.62 Å) Cd–As bond lengths. There are one shorter (2.85 Å) and one longer (3.04 Å) Cd–Br bond lengths. In the second Cd2+ site, Cd2+ is bonded in a rectangular see-saw-like geometry to one As+2.50- and three equivalent Br1- atoms. The Cd–As bond length is 2.60 Å. All Cd–Br bond lengths are 2.81 Å. There are two inequivalent As+2.50- sites. In the first As+2.50- site, As+2.50- is bonded to three equivalent Cd2+ and one As+2.50- atom to form corner-sharing AsCd3As tetrahedra. The As–As bond length is 2.44 Å. In the second As+2.50- site, As+2.50- is bonded to four Cd2+ atoms to form corner-sharing AsCd4 trigonal pyramids. Br1- is bonded in a trigonal non-coplanar geometry to three Cd2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CdP3NO9 by Materials Project

(Cd(PO3)3)2N2 crystallizes in the hexagonal P-6c2 space group. The structure is three-dimensional and consists of two ammonia molecules and one Cd(PO3)3 framework. In the Cd(PO3)3 framework, Cd2+ is bonded to six equivalent O2- atoms to form CdO6 octahedra that share corners with six equivalent PO4 tetrahedra. All Cd–O bond lengths are 2.30 Å. P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent CdO6 octahedra and corners with two equivalent PO4 tetrahedra. The corner-sharing octahedral tilt angles are 38°. There are a spread of P–O bond distances ranging from 1.50–1.62 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Cd2+ and one P5+ atom. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent P5+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Strong Rashba-Dresselhaus Effect in Nonchiral 2D Ruddlesden-Popper Perovskites

Chirality transfer from organic chiral molecules to lead halides is theorized as the origin of the strong Rashba-Dresselhaus effect causing large circular dichroism (CD) and circularly polarized luminescence (CPL) in metal halide perovskites (MHPs). In this report a concrete empirical evidence is provided that such strong CD and CPL can occur even in nonchiral 2D Ruddlesden-Popper perovskites (RPPs) (BA) 2 (MA) n-1 Pb n I 3n+1 (where MA = CH 3 NH 3 and BA = CH 3 (CH 2 ) 3 NH 3 ). The CD and CPL responses occurring at the excitonic transition of the MHPs are strongest (≈100 mdeg and 4.8%, respectively) when a single lead halide octahedral [PbI 6 ] 4- layer is repeatedly stacked between two nonchiral molecules BA + (n = 1). However, they are rapidly quenched as n increases. It is hypothesized that strong Rashba-Dresselhaus splitting in the 2D RPPs originates the strong CD and CPL signatures. Density functional theory calculations reveal that the large interlayer distortions in the inorganic layers at the organic/inorganic interface give rise to the strong Rashba-Dresselhaus splitting. A Rashba-Dresselhaus field of ≈600 and ≈50 mT for n = 1 and 2, respectively, is estimated by magnetic circular dichroism spectroscopy. The studies may have significant impact on designing 2D RPPs with large Rashba-Dresselhaus effects at room temperature for spintronic applications.

circular dichroism↗
DOE OSTI2022

Strong Induced Circular Dichroism in a Hybrid Lead‐Halide Semiconductor Using Chiral Amino Acids for Crystallite Surface Functionalization

Abstract Chirality is a desired property in functional semiconductors for optoelectronic, catalytic, and spintronic applications. Here, introducing enantiomerically‐pure 3‐aminobutyric acid (3‐ABA) into thin films of the 1D semiconductor dimethylammonium lead iodide (DMAPbI 3 ) is found to result in strong circular dichroism (CD) in the optical absorption. X‐ray diffraction and grazing incidence small angle X‐ray scattering (GISAXS) are applied to gain molecular‐scale insights into the chirality transfer mechanism, which is attributed to a chiral surface modification of DMAPbI 3 crystallites. This study demonstrates that the CD signal strength can be controlled by the amino‐acid content relative to the crystallite surface area. The CD intensity is tuned by the composition of the precursor solution and the spin‐coating time, thereby achieving anisotropy factors ( g abs ) as high as 1.75 × 10 –2 . Grazing incidence wide angle scattering reveals strong preferential ordering that can be suppressed via tailored synthesis conditions. Different contributions to the chiroptical properties are resolved by a detailed analysis of the CD signal utilizing an approach based on the Mueller matrix model. This report of a novel class of chiral hybrid semiconductors with precise control over their optical activity presents a promising approach for the design of circularly polarized light detectors and emitters.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Hierarchically Templated Synthesis of 3D‐Printed Crosslinked Cyclodextrins for Lycopene Harvesting

Abstract Plants produce a wide range of bioactive phytochemicals, such as antioxidants and vitamins, which play crucial roles in aging prevention, inflammation reduction, and reducing the risk of cancer. Selectively harvesting these phytochemicals, such as lycopene, from tomatoes through the adsorption method is cost‐effective and energy efficient. In this work, a templated synthesis of 3D‐printed crosslinked cyclodextrin polymers featuring nanotubular structures for highly selective lycopene harvesting is reported. Polypseudorotaxanes formed by triethoxysilane‐based telechelic polyethylene glycols and α‐cyclodextrins (α‐CDs) are designed as the template to (1) synthetically access urethane‐based nanotubular structures at the molecular level, and (2) construct 3D‐printed architectures with designed macroscale voids. The polypseudorotaxane hydrogels showed good rheological properties for direct ink writing, and the 3D‐printed hydrogels were converted to the desired α‐CD polymer network through a three‐step postprinting transformation. The obtained urethane‐crosslinked α‐CD monoliths possess nanotubular structures and 3D‐printed voids. They selectively adsorb lycopene from raw tomato juice, protecting lycopene from photo‐ or thermo‐degradations. This work highlights the hierarchically templated synthesis approach in developing functional 3D‐printing materials by connecting the bottom‐up molecular assembly and synthesis with the top‐down 3D architecture control and fabrication.

Chemistry↗
DOE OSTI2019

Solid Phase Extraction of Cadmium and Lead from Water by Amberlyst 15 and Determination by Flame Atomic Absorption Spectrometry

Preconcentration of Cd(II) and Pb(II) was carried out by using column solid phase extraction method. Amberlyst 15 was used as solid phase for these analytes. The optimum extraction conditions such as pH (4), type and volume of eluent (5 mL of 2 mol L{sup −1} HNO{sub 3}) sample flow rate (1 mL min{sup −1}) and sample volume (100 mL for Cd(II) and 750 mL for Pb(II)) were determined. The recoveries were found for Cd(II) and Pb(II) as 104% ± 1% and 102 % ± 2%, respectively. The limit of detections were found as 0.23 µg L{sup −1} for Cd(II) and 0.13 µg L{sup −1} for Pb(II). The effects of foreign ions were also studied. The method was validated by analyzing standard reference material and spiked water samples. Percent relative error and relative standard deviation were below 3% and 4%, respectively.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Identification of Differentially Expressed Genes of Rice Under Cadmium Stress Using DDRT-PCR Approach

Cadmium (Cd) is one of the hazardous environmental pollutants, and it can be harmful to human health through consumption of food-plants capable of bioaccumulating Cd. Therefore, lowering cadmium accumulation in plants is highly desirable. Here, a rice cultivar ‘Qisanzhan’ was studied using differential display reverse transcription-polymerase chain reaction (DDRT-PCR). Fifty-six differentially expressed genes were found in the root tips of 4-leaf stage rice seedlings exposed to 4 and 12 h of 50 µmol/L Cd(NO{sub 3}){sub 2} in a nutrient solution using DDRT-PCR. Further validation using semi-quantitative RT-PCR showed that the expression patterns of 16 genes were consistent with those found in DDRT-PCR. These genes encode receptor-like protein kinase, pleiotropic drug resistance protein, aquaporin protein, plasma membrane ATPase, etc. The differentially genes identified here can be used to obtain a better understanding of the molecular mechanisms of Cd absorption and accumulation in plants.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Trace Metal Accumulation in Trigonella foenum-graecum Irrigated with Wastewater and Human Health Risk of Metal Access Through the Consumption

The aim of the present research was to determine the trace metal accumulations in Trigonella foenum-graecum irrigated with three different water regimes (ground water, canal water and sugar mill water). Also, transfer factors, pollution load indices, and health risk indices were assessed to evaluate metal transport and accumulation through the food chain. The analysis was conducted by Atomic Absorption Spectrophotometer (Shimadzu model AA-6300) to evaluate the concentration of metals in water, soil and vegetables. Trace metal concentrations in water samples ranged from 0.84 to 1.67, 0.42 to 0.72, 0.45 to 0.85, 2.51 to 9.99, 1.21 to 1.92, 1.82 to 9.98 and 0.64 to 0.91 mg/kg for Cd, Cr, Cu, Fe, Ni, Zn and Mn, respectively. The mean metal concentrations in soil samples were determined as 0.25, 0.86, 0.96, 3.37, 0.4, 0.44 and 2.31 mg/kg for Cd, Cr, Cu, Fe, Ni, Zn and Mn, respectively. Trace metal accumulations in T. foenum-graecum samples gathered from where soil samples were taken are as follows: The contents of Cd, Cr, Cu, Fe, Ni, Zn and Mn ranged from 0.48 to 1.06, 0.11 to 0.35, 0.15 to 0.29, 1.43 to 8.39, 0.39 to 0.54, 2.1 to 3.05 and 0.42 to 0.47 mg/kg, respectively. Statistical analyses showed that the treatments have non-significant effect (p > 0.05) on concentrations of metals in T. foenum-graecum samples collected from three sites for Ni, Cr, Cu, Zn and Mn and significant effect on Fe and Cd.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Effects of Heavy Metals Artificial Contamination on Porcellio laevis (Latreille, 1804) (Crustacea: Isopoda: Oniscidea)

This study aimed at determining the competition of cadmium (Cd), lead (Pb), zinc (Zn) and copper (Cu) on their assimilation, on the food consumption and the growth of terrestrial isopod Porcellio laevis. Individuals were exposed to artificially contaminated litter of Quercus for 4 weeks and were weekly weighed. At the end of the experiment, the concentration of Cd, Pb, Zn and Cu in individuals were measured by atomic absorption spectrometry. Biological parameters such as growth, and bioaccumulation factor (BAF) were calculated and results from the various treatments were compared. Depending on metals, weight loss or gain were recorded for isopods during the four weeks of exposure. A weight loss was measured on individuals exposed to Cd-contaminated litter whereas a weight gain was highlighted for those exposed to the Zn-contaminated litter. BAF values revealed that P. laevis was macroconcentrator of Zn and Cu and deconcentrator of Cd and Pb.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Metal(loid) bioaccessibility and inhalation risk assessment: A comparison between an urban and an industrial area

Highlights: • Metal(loid) bioaccessibility of PM{sub 10} was evaluated with simulated lung fluids. • Most studied metal(loids) were highly bioaccessible in artificial lysosomal fluid. • Metal(loid)s from the industrial site had the highest bioaccessibility. • Elevated non-carcinogenic risk associated with Mn was found at the studied area. • Carcinogenic risk was slightly exceeded for Cd exposure at the industrial location. The content of metal(loid)s in particulate matter (PM) is of special concern due to their contribution to overall (PM) toxicity. In this study, the bioaccessibility and human health risk of potentially toxic metal(loid)s associated with PM{sub 10} were investigated in two areas of the Cantabrian region (northern Spain) with different levels of exposure: an industrial area mainly influenced by a ferromanganese alloy plant; and an urban area consisting mainly of residential and commercial activities, but also affected, albeit to a lesser extent by the ferroalloy plant. Total content and bioaccessible fractions in simulated lung fluids (SLFs) of Fe, Mn, Zn, Ni, Cu, Sb, Mo, Cd and Pb were determined by ICP-MS. Gamble's solution and artificial lysosomal fluid (ALF) were used to mimic different conditions inside the human respiratory system. A health risk assessment was performed based on the United States Environmental Protection Agency's (USEPA) methodology. Most metal(loid)s showed moderate and high bioaccessibility in Gamble's solution and ALF, respectively. Despite the high variability between the samples, metal(loid) bioaccessibility was found to be higher on average at the industrial site, suggesting a greater hazard to human health in the proximity of the main metal(loid) sources. Based on the results of the risk assessment, the non-carcinogenic risk associated with Mn exposure was above the safe limit (HQ> 1) under all the studied scenarios at the industrial site and under some specific scenarios at the urban location. The estimated carcinogenic inhalation risk for Cd exposure at the industrial site was found to be within the range between 1.0 × 10{sup −6} to 1.0 × 10{sup −4} (uncertainty range) under some scenarios. The results obtained in this study indicate that Mn and Cd inhalation exposure occurring in the vicinities of the studied areas may pose a human health risk.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Multiple-metal exposure, diet, and oxidative stress in Uruguayan school children

Highlights: • In 6–8 year-old children, we examined associations between urinary concentrations of arsenic, cadmium, and lead, and urinary F{sub 2}–8α isoprostane and 8-hydroxy-2-deoxy-guanosine (8-OHdG). • Even at low-level, each doubling in urinary arsenic concentrations was associated with ~ 10 ng/mL higher 8-OHdG concentratio. • An indicator of mixture of the three metals was associated with higher 8-OHdG concentrations. • We found no effect modification by children's dietary antioxidant intake. Oxidative stress (OS) is an important consequence of exposure to toxic metals but it is unclear to what extent low-level metal exposures contribute to OS in children. We examined the cross-sectional association between urinary concentrations of arsenic (As), cadmium (Cd), and lead (Pb) and urinary markers of OS: F{sub 2}–8α isoprostane and 8-hydroxy-2-deoxy-guanosine (8-OHdG). We also tested effect modification by dietary intakes. Of the 211 children aged 6–8 years living in Montevideo who were eligible for the study because they had at least one OS marker measured via ELISA, 143 were included in a complete-case analysis. Urinary metals were measured with inductively coupled plasma mass spectrometry (ICP-MS: Pb, Cd) and high-performance liquid chromatography online with hydride generation ICP-MS (As-metabolites); concentrations were log{sub 2}-transformed. All urinary markers were adjusted for specific gravity of urine. Two 24-h dietary recalls were conducted to estimate children's dietary intakes, including total fruit and vegetable consumption and vitamin C, zinc and fiber intake. Ordinary least square (OLS) and weighted quantile sum (WQS) regressions were used to estimate the association between metals and each OS marker as outcome. Metal exposure was generally low: median urinary As, Cd, Pb 9.6 μg/L, 0.06 μg/L and 1.9 μg/L, respectively. Median 8-isoprostane concentration was 1.1 and 8-OHdG 39.6 ng/mL. Log{sub 2}-transformed urinary As concentrations were positively associated with 8-OHdG concentrations (10.90 [3.82, 17.97]) in covariate-adjusted OLS models which also took account of exposure to Cd and Pb. In WQS, a mixture index was also associated with higher 8-OHdG (8.71 [1.12, 16.3] for each 25% increase in index value), mostly driven by As exposure. There was little evidence of effect modification by dietary antioxidants. In sum, even at low-level, As exposure is associated with detectable oxidative damage to the DNA.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Morphological and crystallographic controls in the replacement of calcite and aragonite by cerussite and otavite

Mineral replacement reactions are essential solid-fluid interactions in natural and industrial processes including metasomatism, diagenesis, and metamorphism, and sequestration of metal toxins from polluted water. In this paper, we explore the morphological evolution of aragonite and calcite (polymorphs of CaCO 3 ) during their replacement by cerussite (PbCO 3 , an isomorph of aragonite) and otavite (CdCO 3 , an isomorph of calcite) in acidic aqueous solutions (with initial pH 3 to 4). Observations using scanning electron and synchrotron-based transmission X-ray microscopies reveal the formation of pseudomorphic shells (~5 to 10 µm thick) of cerussite and otavite when Pb 2+ is reacted with either calcite or aragonite and when Cd 2+ is reacted with aragonite. The formation of pore space at the substrate-precipitate interface and within the precipitate is found to be key in promoting chemical exchange between the dissolving phase and the solution. In contrast, minimal reactivity is observed when Cd 2+ is reacted with calcite. These results demonstrate that the lack of substrate-precipitate epitaxy (either because of inconsistent symmetries or due to large lattice constant mismatch) is a critical factor that enables replacement of primary CaCO 3 minerals by Pb- or Cd-bearing secondary minerals while the presence of epitaxial relationships inhibit those reactions. When calcite and aragonite coexist, the replacement of aragonite by cerussite and otavite occurs preferentially over calcite. We postulate that the relative reactivity of calcite and aragonite to Pb 2+ and Cd 2+ can be determined by interplay between morphological and crystallographic properties of CaCO 3 materials as well as solution chemistry. Our results demonstrate that coupled dissolution-precipitation processes of carbonate minerals play an important role in controlling mobility and bioavailability of lead and cadmium in environments where acidic metal-contaminated water interacts with carbonate-rich rocks and soils.

58 GEOSCIENCES↗
DOE OSTI2023

Evolution of dislocation loops and voids in post-irradiation annealed ThO 2 : A combined in-situ TEM and cluster dynamics investigation

The effect of isochronal annealing on the evolution of dislocation loop and void population in proton irradiated ThO 2 has been investigated. Post-irradiation annealing in other actinide oxides like UO 2 shows significant loop coarsening. ThO 2 samples were irradiated with 2 MeV protons up to a dose of 0.1 dpa at 600°C. Post-irradiation isochronal annealing was performed at 600, 800, 1000 and 1100°C for 1 h at each temperature using in-situ TEM. Only faulted 1/3<111> type dislocation loops were observed, and their sizes and distribution were characterized. Further, the population of self-interstitial atom (SIA) dislocation loops did not show any significant growth and coarsening. Additionally, nanometric voids were observed at annealing temperatures of 1000 and 1100°C. Using cluster dynamics (CD), we have studied the nucleation and growth of point defects and defect clusters, i.e., SIA prismatic dislocation loops and nanometric and sub-nanometric voids in proton irradiated ThO 2 . The CD model was further utilized to predict the growth and coarsening of loops and voids during isochronal annealing at the experimental and higher temperatures. The model did not predict significant SIA loop growth which closely corresponds to the TEM observations. CD predicted SIA loop coarsening is insignificant even at high annealing temperature of 1500°C because the model only considers the growth of defect clusters by absorption of like point defects, i.e., SIA loops absorb interstitials and voids absorb vacancies, and cannot account for their migration and coalescence due to elastic interaction. The CD model also predicts the evolution of nanometric voids having mean size within the error bounds of TEM observations.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Computational design of passivants for CdTe grain boundaries

CdTe is the second most-widely deployed photovoltaic (PV) material due to its high efficiency and low manufacturing costs. Currently, polycrystalline CdTe (poly-CdTe) has a record efficiency of similar to 22%, which is still well below the theoretical limit (similar to 30%). Polycrystalline CdTe films that have incorporated Cl or Se show higher efficiency, possibly due to the segregation of these ions to the grain boundaries (GBs), where they may passivate the dangling bonds. However, the efficiency enhancement mechanisms of passivants in CdTe GBs, and the feasibility of employing alternative passivants, have not been well explored. Here, we present a systematic computational study of CdTe GBs with potential passivants, namely S, P, As, Se, and Sb on Te sites, and Na, Mg, Al, Sc, Cu, and Zn on Cd sites. Density functional theory (DFT) calculations were performed on GB dislocation core structures derived from scanning transmission electron microscopy (STEM) images of a model GB (bicrystal). We computed the segregation thermodynamics, electronic density of states, and charge variations near doped CdTe GBs. We find that segregation of impurities to GBs is thermodynamically favorable. For a Te-terminated core, Se, S, and P on Te sites effectively reduce midgap states. For both Cd-and Te-terminated dislocation cores, Sc and Al reduce midgap states when substituted for Cd atoms. Overall, the greatest improvement was achieved with co-doping, i.e. simultaneously substituting Te with Se and substituting Cd with Cu or Al. The elimination of midgap states is predicted to increase the photovoltaic efficiency of CdTe by reducing the recombination at grain boundaries.

14 SOLAR ENERGY↗
DOE OSTI2022

Solvent-Driven Transformation of Zn/Cd 2+ -Deoxycholate Assemblies

Deoxycholic acid (DOC) is a unique, biologically derived surfactant with facial amphiphilicity that has been exploited, albeit minimally, in supramolecular assembly of materials. Here, we present the synthesis and structural characterization of three hybrid metal (Zn 2+ and Cd 2+ )-DOC compounds. Analysis by single-crystal Xray diffraction reveals the many interactions that are possible between these facial surfactants and the influence of solvent molecules that drive the assembly of materials. These structures are the first metal- DOC complexes besides those obtained from alkali and alkaline earth metals. We isolated polymeric chains of both Cd and Zn (Zn poly -DOC and Cd poly -DOC) from water. Major interactions between DOC molecules in these phases are hydrophobic in nature. Cd poly -DOC exhibits unique P1 symmetry, with complete interdigitation of the amphiphiles between neighboring polymeric chains. Zn 4 -DOC, obtained from methanol dissolution of Zn poly -DOC, features the OZn 4 tetrahedron, widely known in basic zinc acetate and MOF-5 (metal organic framework). We document a solvent-driven, roomtemperature transition between Zn poly -DOC and Zn 4 -DOC (in both directions) by scanning and transmission electron microscopies in addition to small-angle X-ray scattering, powder X-ray diffraction, and infrared spectroscopy. These studies show the methanoldriven transition of Zn poly -DOC to Zn 4 -DOC occurs via an intermediate with no long-range order of the Zn 4 clusters, indicating the strongest interactions driving assembly are intramolecular. On the contrary, water-driven solid-to-solid transformation from Zn 4 -DOC to Zn poly -DOC exhibits crystal-to-crystal transformation. Zn poly -DOC is robust, easy to synthesize, and comprised of biologically benign components, so we demonstrate dye absorption as a proxy for water treatment applications. It favors absorption of positively charged dyes. These studies advance molecular level knowledge of the supramolecular assembly of facial surfactants that can be exploited in the design of organic-inorganic hybrid materials. This research also highlights the potential of solvent for tuning supramolecular assembly processes, leading to new hybrid materials featuring facial surfactants.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗