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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Vapor-Liquid Partitioning of Methylmercury Compounds: Fundamental Data to Support the Savannah River Site Liquid Waste System: Henry's Law, Solubility and Vapor Pressure Determination for Representative Methylmercury Compounds

The Savannah River Site (SRS) Liquid Waste System (LWS) contains approximately 66 tons of mercury within the liquids, salts, and sludges that are currently being processed into final wasteforms for disposal. Mercury concentrations within the system exceed those typically experienced in environmental or industrial systems; thus, management of mercury compounds continues to be a priority for SRS. In the LWS, waste is vitrified into a borosilicate glass wasteform that contains most of the radioactivity, while the lower activity solutions are dispositioned in a low-level grout wasteform, or “saltstone”. The alkaline, high ionic strength caustic wastes are pumped, evaporated, and otherwise managed throughout the LWS and Defense Waste Processing Facility (DWPF) as they are stored and prepared for conversion to the final wasteforms. Because of the complexity of this system, a key component of effective mercury management in the LWS requires analysis of mercury in various physical phases. The high concentration of mercury within the SRS LWS has the potential to generate vapor-phase contamination. Elemental mercury (Hg 0 ), dimethylmercury ((CH 3 ) 2 Hg), and methylmercury (CH 3 Hg + ) are among species known or suspected to contribute to the flux of mercury from liquid to vapor phase (Iverfeldt and Lindquist, 1982). Chemical speciation affects not only mercury behavior in LWS operations but may also affect the performance of mercury treatment and removal technologies in the LWS.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Benzenesulfonamide Derivatives as Complexants and Extractants for Addressing the Mercury Problem at the Savannah River Site

Mercury (Hg) is a major global pollutant arising from both natural and anthropogenic sources. Its widespread use in medicinal and industrial applications makes it a common chemical exposure and environmental pollutant. It can exist in several forms which include: Metallic mercury (Hg{sup 0}), mercurous (Hg{sub 2}{sup 2+}), mercuric salts (Hg{sup 2+}), and organic mercury (e.g. CH{sub 3}Hg{sup +}), with the latter being the most toxic of all the species. Due to mercury's high toxicity, new approaches towards its detection has received significant attention in the scientific community. Mercury exposure at the Savannah River Site (SRS) has been a recent concern especially with increasing amounts of organic mercury in the saltstone. It originates mainly from its use as an acidic dissolution catalyst of aluminum cladding from target fuels within the uranium and plutonium processing operations [1]. It is present to an amount of about 60 metric tons in the high-level waste (HLW) tanks. Organic Mercury species have been found in low activity waste (LAW) at the site that eventually ends up in the saltstone. Therefore, there is a need for: i) Converting organic mercury to other less toxic forms and ii) Complexation and removal of Hg prior of disposal of LAW in saltstone. Various methods have been developed for selective sensing of mercury in the presence of other toxic metals. These methods include using ligands that can form organo-soluble metal complexes with different optical and spectroscopic properties that can be used for toxic metal sensing. In 2005, our group pioneered an ion-exchange extraction method, in which o-phenylenediamine-derived disulfonamides were used to complex and selectively extract and sense Pb{sup 2+} from aqueous solutions into an organic phase [2,3]. Herein, a disulfonamide and a bis-dansylamide have been shown to extract, complex and sense Hg(II). Ligand 1: The crystal structure of the disulfonamide-Hg complex confirms the complexation of Hg(II) with the ligand. Complexation was corroborated by the {sup 1}H-NMR spectra obtained after contacting solutions of various concentrations of Hg{sup 2+} with 2 mM ligand in chloroform. Distinct resonances are observed at Hg/L ratio of 0.5 that are also observed for the isolated 1:2 complex. In the presence of excess mercury, new resonances, as well as the movement of Et{sub 3}N resonances indicate the formation of a different Hg-sulfonamide-triethylamine complex, presumably having 1:1 Hg:L stoichiometry. The electronic spectra of aqueous phases after extraction show that there was no free ligand absorption at 0.5 eq of Hg, indicating a complete complexation. Complexation was also confirmed by the UV-visible titrations with Hg{sup 2+} at constant ligand concentration. pH-dependent extraction carried out shows that extraction of Hg(II) by ligand 1 was over 90% for most alkaline pHs. Ligand 2: The crystal structure of the Ligand 2 complex formed with Hg(OAc){sub 2} shows a remarkable coordination pattern with 4:2 metal:ligand stoichiometry. The fluorescent bis-dansyl disulfonamide derivative was found to complex and sense HgCl{sub 2} and Hg(OAc){sub 2} by demonstrating fluorescence quenching upon Hg(II) addition in comparison with other metals (Zn(II), Cd(II), Pb(II)). No were observed for Cu(II), Ag(I) and Co(II). We have shown the complexation of Hg(II) by a disulfonamide and a bis-dansyl disulfonamide ligand using several spectroscopic methods. Ligand 1 was able to extract mercury into chloroform and form a complex in the presence of excess mercury by synergistic complexation with triethylamine acting as a co-ligand. X-ray and NMR both confirm a 1:2 HgL{sub 2} stoichiometry. Ligand 2 can be used for sensing of Hg(II) as fluorescence quenching was observed after addition of Hg(II)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

Review of Mercury Sequestration in Cementitious Waste Forms

Decontaminated salt solution from Tank 50 at the Savannah River Site (SRS) is known to contain dissolved mercury species which are present as hydroxides and oxides. These species are reported in analytical measurements as the organic cation [CH 3 Hg] + and the inorganic cation Hg 2+ . The salt solution is mixed with cementitious reagents, blast-furnace slag (BFS) and thermally beneficiated Class F fly ash in the Saltstone Processing Facility and pumped into engineered Saltstone Disposal Units, (SDUs), to produce a solidified waste form. The solidified waste form, saltstone, encapsulates and chemically stabilizes the mercury and other contaminants, sequestering them from release into the environment. With the discovery of methylmercury in the salt solution, testing was performed to determine the extent to which saltstone prepared with methylmercury (MeHg) retains mercury in the Toxicity Characteristic Leaching Procedure (TCLP). Results from this testing indicated that the amount of mercury extracted remained below the regulatory limit, and that the saltstone formulation with a greater proportion of BFS performed slightly better at retaining Hg in the solid.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Materials Data on HgC2(SN)2 by Materials Project

Hg(SCN)2 crystallizes in the triclinic P1 space group. The structure is two-dimensional and consists of one Hg(SCN)2 sheet oriented in the (0, 0, 1) direction. Hg2+ is bonded to four N3- and two S2- atoms to form edge-sharing HgS2N4 octahedra. There are three shorter (2.84 Å) and one longer (2.86 Å) Hg–N bond lengths. Both Hg–S bond lengths are 2.45 Å. There are two inequivalent C4+ sites. In the first C4+ site, C4+ is bonded in a distorted linear geometry to one N3- and one S2- atom. The C–N bond length is 1.18 Å. The C–S bond length is 1.65 Å. In the second C4+ site, C4+ is bonded in a distorted linear geometry to one N3- and one S2- atom. The C–N bond length is 1.18 Å. The C–S bond length is 1.65 Å. There are two inequivalent N3- sites. In the first N3- site, N3- is bonded in a distorted single-bond geometry to two equivalent Hg2+ and one C4+ atom. In the second N3- site, N3- is bonded in a distorted single-bond geometry to two equivalent Hg2+ and one C4+ atom. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a water-like geometry to one Hg2+ and one C4+ atom. In the second S2- site, S2- is bonded in a water-like geometry to one Hg2+ and one C4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Metal-Mediated DNA Nanotechnology in 3D: Structural Library by Templated Diffraction

DNA double helices containing metal-mediated DNA (mmDNA) base pairs are constructed from Ag + and Hg 2+ ions between pyrimidine:pyrimidine pairs with the promise of nanoelectronics. Rational design of mmDNA nanomaterials is impractical without a complete lexical and structural description. Here, in this study, the programmability of structural DNA nanotechnology toward its founding mission of self-assembling a diffraction platform for biomolecular structure determination is explored. The tensegrity triangle is employed to build a comprehensive structural library of mmDNA pairs via X-ray diffraction and generalized design rules for mmDNA construction are elucidated. Two binding modes are uncovered: N3-dominant, centrosymmetric pairs and major groove binders driven by 5-position ring modifications. Energy gap calculations show additional levels in the lowest unoccupied molecular orbitals (LUMO) of mmDNA structures, rendering them attractive molecular electronic candidates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

A combinatory ferroelectric compound bridging simple ABO 3 and A-site-ordered quadruple perovskite

The simple ABO 3 and A-site-ordered AA' 3 B 4 O 12 perovskites represent two types of classical perovskite functional materials. There are well-known simple perovskites with ferroelectric properties, while there is still no report of ferroelectricity due to symmetry breaking transition in A-site-ordered quadruple perovskites. Here we report the high pressure synthesis of an A-site-ordered perovskite PbHg 3 Ti 4 O 12 , the only known quadruple perovskite that transforms from high-temperature centrosymmetric paraelectric phase to low-temperature non-centrosymmetric ferroelectric phase. The coordination chemistry of Hg 2+ is changed from square planar as in typical A-site-ordered quadruple perovskite to a rare stereo type with 8 ligands in PbHg 3 Ti 4 O 12 . Thus PbHg 3 Ti 4 O 12 appears to be a combinatory link from simple ABO 3 perovskites to A-site-ordered AA' 3 Ti 4 O 12 perovskites, sharing both displacive ferroelectricity with former and structure coordination with latter. This is the only example so far showing ferroelectricity due to symmetry breaking phase transition in AA' 3 B 4 O 12 -type A-site-ordered perovskites, and opens a direction to search for ferroelectric materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HgH4C2S2(N3Cl)2 by Materials Project

Hg(N2)2(CNHS)2(HCl)2 crystallizes in the orthorhombic Pbcn space group. The structure is zero-dimensional and consists of eight hydrochloric acid molecules, eight isothiocyanic acid molecules, four mercury molecules, and eight nitrogen molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HgN4(ClO4)2 by Materials Project

Hg(N2)2(ClO4)2 is Iron carbide-derived structured and crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of sixteen ammonia molecules, four mercury molecules, and eight ClO4 clusters. In each ClO4 cluster, there are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one Cl1- atom. The O–Cl bond length is 1.47 Å. In the second O2- site, O2- is bonded in a single-bond geometry to one Cl1- atom. The O–Cl bond length is 1.48 Å. In the third O2- site, O2- is bonded in a single-bond geometry to one Cl1- atom. The O–Cl bond length is 1.44 Å. In the fourth O2- site, O2- is bonded in a single-bond geometry to one Cl1- atom. The O–Cl bond length is 1.45 Å. Cl1- is bonded in a tetrahedral geometry to four O2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on FeHg2C6S2(NO2)2 by Materials Project

Fe(Hg(NCS))2(CO)4 crystallizes in the tetragonal I4_1/a space group. The structure is one-dimensional and consists of eight ferrum molecules; thirty-two formaldehyde molecules; and four Hg(NCS) ribbons oriented in the (0, 0, 1) direction. In each Hg(NCS) ribbon, Hg2+ is bonded in an L-shaped geometry to one N3- and one S2- atom. The Hg–N bond length is 2.90 Å. The Hg–S bond length is 2.61 Å. C+1.83+ is bonded in a distorted linear geometry to one N3- and one S2- atom. The C–N bond length is 1.18 Å. The C–S bond length is 1.66 Å. N3- is bonded in a distorted single-bond geometry to one Hg2+ and one C+1.83+ atom. S2- is bonded in a water-like geometry to one Hg2+ and one C+1.83+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hg(SbS2)4 by Materials Project

Hg(SbS2)2(SbS2)2 is Stibnite-derived structured and crystallizes in the monoclinic C2/c space group. The structure is two-dimensional and consists of two Hg(SbS2)2 sheets oriented in the (1, 0, 0) direction and two SbS2 sheets oriented in the (1, 0, 0) direction. In each Hg(SbS2)2 sheet, there are two inequivalent Hg2+ sites. In the first Hg2+ site, Hg2+ is bonded in a distorted linear geometry to six S2- atoms. There are a spread of Hg–S bond distances ranging from 2.38–3.44 Å. In the second Hg2+ site, Hg2+ is bonded in a distorted linear geometry to six S2- atoms. There are a spread of Hg–S bond distances ranging from 2.38–3.45 Å. There are two inequivalent Sb+3.50+ sites. In the first Sb+3.50+ site, Sb+3.50+ is bonded to five S2- atoms to form edge-sharing SbS5 square pyramids. There are a spread of Sb–S bond distances ranging from 2.49–2.94 Å. In the second Sb+3.50+ site, Sb+3.50+ is bonded to five S2- atoms to form edge-sharing SbS5 square pyramids. There are a spread of Sb–S bond distances ranging from 2.49–2.94 Å. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded in a 5-coordinate geometry to two equivalent Hg2+ and three Sb+3.50+ atoms. In the second S2- site, S2- is bonded in a distorted trigonal non-coplanar geometry to one Hg2+ and two equivalent Sb+3.50+ atoms. In the third S2- site, S2- is bonded in a 5-coordinate geometry to two equivalent Hg2+ and three Sb+3.50+ atoms. In the fourth S2- site, S2- is bonded in a distorted trigonal non-coplanar geometry to one Hg2+ and two equivalent Sb+3.50+ atoms. In each SbS2 sheet, there are two inequivalent Sb+3.50+ sites. In the first Sb+3.50+ site, Sb+3.50+ is bonded to five S2- atoms to form distorted edge-sharing SbS5 square pyramids. There are a spread of Sb–S bond distances ranging from 2.50–3.00 Å. In the second Sb+3.50+ site, Sb+3.50+ is bonded to five S2- atoms to form distorted edge-sharing SbS5 square pyramids. There are a spread of Sb–S bond distances ranging from 2.50–3.02 Å. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded in a 3-coordinate geometry to two equivalent Sb+3.50+ and one S2- atom. The S–S bond length is 2.08 Å. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three equivalent Sb+3.50+ atoms. In the third S2- site, S2- is bonded in a 3-coordinate geometry to two equivalent Sb+3.50+ and one S2- atom. In the fourth S2- site, S2- is bonded in a 3-coordinate geometry to three equivalent Sb+3.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2022

First observation of the decay of the 13/2 + isomer in 183 Hg and B(M 2) systematics of neutron transitions across the nuclear chart

The decay of the 13/2 + isomeric state in 183 Hg was observed for the first time following the a decay of the 13/2 + isomer in 187 Pb produced in the 142 Nd( 50 Cr, 2p3n) reaction. Using $\alpha - \gamma$ delayed coincidence measurements, the half-life of this isomer was measured to be 290(30) μs. This isomer is proposed to deexcite by an unobserved low-energy M2 transition to the known 9/2 - member of a strongly prolate-deformed 7/2 - [514] band, followed by a 105-keV M1 transition to the bandhead. A lower limit of B(M2) >= 0.018 W.u. was deduced for the unobserved transition. The presumed retardation is proposed to be due to the notable shape change between the initial, nearly spherical, and the final, strongly deformed, states. A similar scenario is also considered for the 13/2 + isomer in 181 Hg, suggesting both are cases of shape isomers. The B(M2) systematics of neutron transitions across the nuclear chart is discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Reversible CO 2 Hydrogenation, Neutron Crystallography, and Hydride Reactivity of a Triiridium Heptahydride Complex

Abstract The authors report the structure, reactivity, and catalytic utility of a triiridium complex, [Ir 3 H 6 ( μ 3 ‐H)(PN) 3 ] 2+ ( 2‐H , PN = (2‐pyridyl)CH 2 PBu t 2 ). Despite its unusual stability to unsaturated organics, electrophiles, and even CF 3 SO 3 D, they find that complex 2‐H catalyzes hydrogenation of CO 2 to formate (TON Ir = 9600) and reverse formic acid dehydrogenation (TON Ir = 54 400). The hydrogenation operates via a reactive intermediate [Ir 3 H 4 ( μ ‐H) 4 (PN) 3 ] + ( 5 ). Neutron crystallography and DFT‐supported neutron vibrational spectroscopy of 2‐H reveal Ir─H bond lengths and elucidate the vibration modes within the Ir 3 H 7 core. Stoichiometric oxidation of 2‐H produces four classes of iridium complexes of varied nuclearity and hydride structure: tetra‐ and pentanuclear clusters [Ir 3 H 6 ( μ 3 ‐AuPPh 3 )(PN) 3 ] 2+ ( 2‐Au ) and [Ag{Ir 2 H 4 ( μ ‐OAc)(PN) 2 } 2 ] 3+ ( 6 ) are generated using AuPPh 3 + and AgOAc, respectively. Further oxidation to class [Ir 2 H 3 ( μ ‐X) 2 (PN) 2 ] + is possible with AgOAc, Hg(OAc) 2 , or I 2 . Finally, a TEMPO/HCl system completely oxidizes the hydrides and gives [Ir 2 Cl 4 ( μ ‐Cl) 2 (PN) 2 ] ( 11 ).

Cherepakhin, Valeriy [Loker Hydrocarbon Research I↗
DOE OSTI2025

Reversible CO 2 Hydrogenation, Neutron Crystallography, and Hydride Reactivity of a Triiridium Heptahydride Complex

Here, the authors report the structure, reactivity, and catalytic utility of a triiridium complex, [Ir 3 H 6 (μ 3 -H)(PN) 3 ] 2+ (2-H, PN = (2-pyridyl)CH 2 PBu t 2 ). Despite its unusual stability to unsaturated organics, electrophiles, and even CF 3 SO 3 D, they find that complex 2-H catalyzes hydrogenation of CO 2 to formate (TON Ir = 9600) and reverse formic acid dehydrogenation (TON Ir = 54 400). The hydrogenation operates via a reactive intermediate [Ir 3 H 4 (μ-H) 4 (PN) 3 ] + (5). Neutron crystallography and DFT-supported neutron vibrational spectroscopy of 2-H reveal Ir─H bond lengths and elucidate the vibration modes within the Ir 3 H 7 core. Stoichiometric oxidation of 2-H produces four classes of iridium complexes of varied nuclearity and hydride structure: tetra- and pentanuclear clusters [Ir 3 H 6 (μ 3 -AuPPh 3 )(PN) 3 ] 2+ (2-Au) and [Ag{Ir 2 H 4 (μ-OAc)(PN) 2 } 2 ] 3+ (6) are generated using AuPPh 3 + and AgOAc, respectively. Further oxidation to class [Ir 2 H 3 (μ-X) 2 (PN) 2 ] + is possible with AgOAc, Hg(OAc) 2 , or I 2 . Finally, a TEMPO/HCl system completely oxidizes the hydrides and gives [Ir 2 Cl 4 (μ-Cl) 2 (PN) 2 ] (11).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Competitive exchange between divalent metal ions [Cu(II), Zn(II), Ca(II)] and Hg(II) bound to thiols and natural organic matter

Mercuric Hg(II) ion forms exceptionally strong complexes with various organic ligands, particularly thiols and dissolved organic matter (DOM) in natural water. Few studies, however, have experimentally determined whether or not the presence of base cations and transition metal ions, such as Ca(II), Cu(II), and Zn(II), would compete with Hg(II) bound to these ligands, as concentrations of these metal ions are usually orders of magnitude higher than Hg(II) in aquatic systems. Different from previous model predictions, a significant fraction of Hg(II) bound to cysteine (CYS), glutathione (GSH), or DOM was found to be competitively exchanged by Cu(II), but not by Zn(II) or Ca(II). About 20–75% of CYS-bound-Hg(II) [at 2:1 CYS:Hg(II)] and 14–40% of GSH-bound-Hg(II) [at 1:1 GSH:Hg(II)] were exchanged by Cu(II) at concentrations 1–3 orders of magnitude greater than Hg(II). Competitive exchange was also observed between Cu(II) and Hg(II) bound to DOM, albeit to a lower extent, depending on relative abundances of thiol and carboxylate functional groups on DOM and their equilibrium time with Hg(II). When complexed with ethylenediaminetetraacetate (EDTA), most Hg(II) could be exchanged by Cu(II) and Zn(II), as well as Ca(II) at increasing concentrations. Furthermore, these results shed additional light on competitive exchange reactions between Hg(II) and coexisting metal ions and have important implications in Hg(II) chemical speciation and biogeochemical transformation, particularly in contaminated environments containing relatively high concentrations of Hg(II) and metal ions.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HgH12(ClO7)2 by Materials Project

Hg(H2O)6(ClO4)2 crystallizes in the trigonal P-3m1 space group. The structure is zero-dimensional and consists of two ClO4 clusters and one Hg(H2O)6 cluster. In each ClO4 cluster, there are two inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.47 Å. In the second O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.45 Å. Cl is bonded in a tetrahedral geometry to four O atoms. In the Hg(H2O)6 cluster, Hg is bonded in an octahedral geometry to six equivalent O atoms. All Hg–O bond lengths are 2.40 Å. H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.98 Å. O is bonded in a distorted water-like geometry to one Hg and two equivalent H atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Analysis of Solids Obtained from 201O, 201P, 202A, and 202B Contactors in the Salt Waste Processing Facility

In December 2022, Savannah River Mission Completion personnel recovered solids samples from four contractors (EXT-001, EXT-007, EXT-031, and EXT-040) employed at the Salt Waste Processing Facility (SWPF). These solids were submitted to Savannah River National Laboratory for analysis and characterization. This Technical Report outlines the analytical findings and observations associated with these samples and explores the potential source of solid generation within the SWPF. The following conclusions are offered as a result of this work: the light color solids recovered from EXT-007 are consistent with crystallized, soluble salt components (such as sodium nitrate, sodium hydroxide, and sodium carbonate), all of which can be easily re-dissolved in process water and do not represent a threat to SWPF CSSX processing. While the light solids from the top of EXT-040 were not analyzed, it is believed that they share similar characteristics to those recovered from EXT-007; The dark color solids recovered from EXT-001, EXT-031, and the inside of EXT-040 appear to be complex, consisting of several different types of solids: High concentrations of mercury (Hg, 40-75% by mass) partially present as elemental Hg are consistent with the precipitation of Hg 0 /Hg 2+ from disproportionation of Hg + species in pH swing conditions; Moderate concentrations of titanium (Ti) (2-7%, by mass) are also present, often co-located with Hg. This is consistent with co-precipitation, entrainment, and/or amalgamation of Ti and Hg; Moderate concentrations of iron (Fe) (1-3%, by mass) are observed in SWPF solids and are likely attributable to erosion of stainless-steel components within the CSSX process; Small concentrations of tungsten (W) and cobalt (Co) (<1%, by mass) are observed in SWPF solids. The presence of these solids is consistent with the erosion of components coated with W and Co (e.g., Stellite); Small concentrations of aluminum (Al) (<1%, by mass) are observed in the form of gibbsite and potentially sodium aluminosilicate. The presence of these compounds is likely attributable to the pH swing observed between the scrub and extraction cycles within the CSSX process. The following recommendations are made as a result of this work: Testing should be performed to determine the chemical drivers, process, and mechanism of Hg precipitation in CSSX processing. Special care should be taken to include titanium in tests to evaluate the potential for co-precipitation, entrainment, and amalgamation; Hg-mitigation options that would minimize or eliminate risks of Hg precipitation and solids accumulation (e.g., Hg-absorption techniques, ion exchange/adsorbents, flowsheet changes, etc.) should be assessed.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

Pressure-induced ferroelectric-like transition creates a polar metal in defect antiperovskites Hg3Te2X2 (X = Cl, Br)

Abstract Ferroelectricity is typically suppressed under hydrostatic compression because the short-range repulsions, which favor the nonpolar phase, increase more rapidly than the long-range interactions, which prefer the ferroelectric phase. Here, based on single-crystal X-ray diffraction and density-functional theory, we provide evidence of a ferroelectric-like transition from phase I 2 1 3 to R 3 induced by pressure in two isostructural defect antiperovskites Hg 3 Te 2 Cl 2 (15.5 GPa) and Hg 3 Te 2 Br 2 (17.5 GPa). First-principles calculations show that this transition is attributed to pressure-induced softening of the infrared phonon mode Γ 4 , similar to the archetypal ferroelectric material BaTiO 3 at ambient pressure. Additionally, we observe a gradual band-gap closing from ~2.5 eV to metallic-like state of Hg 3 Te 2 Br 2 with an unexpectedly stable R 3 phase even after semiconductor-to-metal transition. This study demonstrates the possibility of emergence of polar metal under pressure in this class of materials and establishes the possibility of pressure-induced ferroelectric-like transition in perovskite-related systems.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hg2Te4Xe3(O2F13)2 by Materials Project

(XeF2)3(HgTe2(OF5)2)2 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four HgTe2(OF5)2 clusters and six XeF2 clusters. In each HgTe2(OF5)2 cluster, Hg is bonded in a linear geometry to two O atoms. There are one shorter (2.06 Å) and one longer (2.07 Å) Hg–O bond lengths. There are two inequivalent Te sites. In the first Te site, Te is bonded in an octahedral geometry to one O and five F atoms. The Te–O bond length is 1.87 Å. There is two shorter (1.88 Å) and three longer (1.89 Å) Te–F bond length. In the second Te site, Te is bonded in an octahedral geometry to one O and five F atoms. The Te–O bond length is 1.88 Å. There are a spread of Te–F bond distances ranging from 1.87–1.89 Å. There are two inequivalent O sites. In the first O site, O is bonded in a bent 120 degrees geometry to one Hg and one Te atom. In the second O site, O is bonded in a bent 120 degrees geometry to one Hg and one Te atom. There are ten inequivalent F sites. In the first F site, F is bonded in a single-bond geometry to one Te atom. In the second F site, F is bonded in a single-bond geometry to one Te atom. In the third F site, F is bonded in a single-bond geometry to one Te atom. In the fourth F site, F is bonded in a single-bond geometry to one Te atom. In the fifth F site, F is bonded in a single-bond geometry to one Te atom. In the sixth F site, F is bonded in a single-bond geometry to one Te atom. In the seventh F site, F is bonded in a single-bond geometry to one Te atom. In the eighth F site, F is bonded in a single-bond geometry to one Te atom. In the ninth F site, F is bonded in a single-bond geometry to one Te atom. In the tenth F site, F is bonded in a single-bond geometry to one Te atom. In each XeF2 cluster, Xe is bonded in a linear geometry to two F atoms. There are one shorter (2.08 Å) and one longer (2.09 Å) Xe–F bond lengths. There are two inequivalent F sites. In the first F site, F is bonded in a single-bond geometry to one Xe atom. In the second F site, F is bonded in a single-bond geometry to one Xe atom.

36 MATERIALS SCIENCE↗