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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Cool circumgalactic gas in galaxy clusters: connecting the DESI legacy imaging survey and SDSS DR16 Mg ιι absorbers

Herein we investigate the cool gas absorption in galaxy clusters by cross-correlating Mg II absorbers detected in quasar spectra from data release 16 of the Sloan Digital Sky Survey (SDSS) with galaxy clusters identified in the Dark Energy Spectroscopic Instrument (DESI) survey. We find significant covering fractions (⁠1–5percent within r 500 , depending on the chosen redshift interval), ~4–5 times higher than around random sightlines. While the covering fraction of cool gas in clusters decreases with increasing mass of the central galaxy, the total Mg II mass within r 500 is none the less ~10 times higher than for SDSS luminous red galaxies. The Mg II covering fraction versus impact parameter is well described by a power law in the inner regions and an exponential function at larger distances. The characteristic scale of the transition between these two regimes is smaller for large equivalent width absorbers. Cross-correlating Mg II absorption with photo–z selected cluster member galaxies from DESI reveals a statistically significant connection. The median projected distance between Mg II absorbers and the nearest cluster member is ~200 kpc, compared to ~500 kpc in random mocks with the same galaxy density profiles. We do not find a correlation between Mg II strength and the star formation rate of the closest cluster neighbour. This suggests that cool gas in clusters, as traced by Mg II absorption, is: (i) associated with satellite galaxies, (ii) dominated by cold gas clouds in the intracluster medium, rather than by the interstellar medium of galaxies, and (iii) may originate in part from gas stripped from these cluster satellites in the past.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

New isomeric transition in Mg 36 : Bridging the N = 20 and N = 28 islands of inversion

Here, we observed a new isomeric γ transition at 168 keV in 36 Mg, with a half-life of T1/2=90⁢($^{+410}_{-50}$) ns. We propose that the observed transition deexcites a new 0 + isomeric state at 833 keV and populates the previously known first 2 + state. The existence of this isomer is consistent with the predictions of the large-scale shell-model calculations of 36 Mg using the sdpf-u-mix interaction. The observed excitation energy of the second 0 + state is caused by the small energy separation between two prolate-deformed configurations where the intruder configuration corresponds to two-neutron excitations from the sd to the pf shell. Within this interpretation, 36 Mg becomes the crossing point between nuclei in which ground state deformed/superdeformed configurations are caused by the dominance of N=20 intruders ( 32,34 Mg) and nuclei where deformed configurations are associated with the breaking of the N=28 closure and a large occupancy of the 1⁢p 3/2 neutron orbit ( 38 Mg and beyond). We found the lack of three-body monopole corrections in other effective interactions results in a predominance of N=20 intruder configurations past 38 Mg incompatible with our observation. We conclude that 36 Mg bridges the N=20 and N=28 islands of inversion, forming the so-called big island of deformation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1983

FUN with PANURGE - High mass resolution ion microprobe measurements of Mg in Allende inclusions

Isotopic ratios have been determined, at a precision level approaching that of counting statistics using beam switching, by employing PANURGE, a modified CAMECA IMS3F ion microprobe at a mass resolving power of 5000. This technique is used to determine the isotopic composition of Mg and Si and the atomic ratio of Al/Mg in minerals from the Allende inclusion WA and the Allende FUN inclusion C1. Results show enrichment in Mg-26 of up to 260 percent. Results of Mg and Al/Mg measurements on cogenetic spinel inclusion and host plagiclase crystals show Mg-Al isochrons in excellent agreement with precise mineral isochrons determined by thermal emission mass spectrometry. The measurements are found to confirm the presence of substantial excess Mg-26 in WA and its near absence in C1. Data is obtained which indicates a metamorphic reequilibrium of Mg in Allende plagioclase at least 0.6 my after WA formation. Ion probe measurements are obtained which confirm that the Mg composition in Allende C1 is highly fractionated and is uniform among pyroxene, melilite, plagioclase, spinel crystals, and spinel included in melilite and plagioclase crystals.

Huneke, J. C.↗
NASA NTRS1992

Estimates of solar variability using the solar backscatter ultraviolet (SBUV) 2 Mg II index from the NOAA 9 satellite

The Mg II core to wing index was first developed for the Nimbus 7 solar backscatter ultraviolet (SBUV) instrument as an indicator of solar variability on both solar 27-day rotational and solar cycle time scales. This work extends the Mg II index to the NOAA 9 SBUV 2 instrument and shows that the variations in absolute value between Mg II index data sets caused by interinstrument differences do not affect the ability to track temporal variations. The NOAA 9 Mg II index accurately represents solar rotational modulation but contains more day-to-day noise than the Nimbus 7 Mg II index. Solar variability at other UV wavelengths is estimated by deriving scale factors between the Mg II index rotational variations and at those selected wavelengths. Based on the 27-day average of the NOAA 9 Mg II index and the NOAA 9 scale factors, the solar irradiance change from solar minimum in September 1986 to the beginning of the maximum of solar cycle 22 in 1989 is estimated to be 8.6 percent at 205 nm, 3.5 percent at 250 nm, and less than 1 percent beyond 300 nm.

Cebula, Richard P.↗
NASA NTRS2019

Modeling Mg II During Solar Flares. I. Partial Frequency Redistribution, Opacity, and Coronal Irradiation

The Interface Region Imaging Spectrograph has routinely observed the flaring Mg II near-ultraviolet (NUV) spectrum, offering excellent diagnostic potential and a window into the location of energy deposition. A number of studies have forward-modeled both the general properties of these lines and specific flare observations. Generally these have forward-modeled radiation via post-processing of snapshots from hydrodynamic flare simulations through radiation transfer codes. There has, however, not been a study of how the physics included in these radiation transport codes affects the solution. A baseline setup for forward-modeling Mg II in flares is presented and contrasted with approaches that add or remove complexity. It is shown for Mg II that (1) partial frequency distribution (PRD) is still required during flare simulations despite the increased densities; (2) using full angle-dependent PRD affects the solution but takes significantly longer to process a snapshot; (3) including Mg I in non-LTE (NLTE) results in negligible differences to the Mg II lines but does affect the NUV quasi-continuum; (4) only hydrogen and Mg II need to be included in NLTE; (5) ideally the nonequilibrium hydrogen populations, with nonthermal collisional rates, should be used rather than the statistical equilibrium populations; (6) an atom consisting of only the ground state, h and k upper levels, and continuum level is insufficient to model the resonance lines; and (7) irradiation from a hot, dense flaring transition region can affect the formation of Mg II. We discuss modifications to the RH code allowing straightforward inclusion of the transition region and coronal irradiation in flares.

Kerr, Graham S.↗
NASA NTRSDate not supplied

A Combined Al-Mg/Pb-Pb Age of the Solar System

Astrophysical models of planet formation and protoplanetary disk evolution demand precise and accurate timing of the sequence of events in the solar nebula, relative to a time t=0, usually taken to be during the short epoch of CAI (Ca-rich, Al-rich inclusion) formation. Most CAIs formed withlive26Al (mean-life τ26= 1.034 Myr [1]), with an abundance 26Al/27Al ≈ (26Al/27Al)SS= 5.23 × 10-5[2]. We adopt this as the widespread level of 26Al in the solar nebula at t=0. Assuming spatial homogeneity of 26Al, an inclusion that had less 26Al, (26Al/27Al)0, formed a time Δt26= τ26ln[(26Al/27Al)SS/ (26Al/27Al)0] after t=0.These ages are typical precise to within ±0.1 Myr. Igneous bulk meteorites and inclusions can be relatively dated by the Al-Mg chronometer, but only ifΔt26<6 Myr. The Pb-Pb system is useful as a longer relative chronometer. It yields absolute ages tPb using 207Pb/206Pb, 206Pb/204Pb, and 238U/235U ratios measured indifferent portions of a sample, assuming certain half-lives [4]. These absolute ages are uncertain to within ±9 Myr due to uncertainties in the 235U half-life[3], but times of formation ΔtPb= tCAI–tPb relative to t=0, are more precise(±0.5Myr),iftCAI can be found. Here, tCAI means the Pb-Pb age that would be measured in CAIs using the half-lives the community typically uses, if they achieved isotopic closure at t=0. Unfortunately, direct Pb-Pb dating of CAIs has not definitively determined tCAI. Based on four CAIs with canonical (26Al/27Al)0,[5,6] found tPb= 4567.30 ± 0.16 Myr. No other CAI ages with measured 238U/235U have been reported in the refereed literature, but there are hints of other CAIs with ages tPb= 4568.0 ± 0.2 Myr [7] and tPb= 4568.3 ± 0.2 Myr [8].It is unclear whether anyof these igneous type B CAIs isotopically closed at t=0 or represents tCAI. Instead of measurements, we advocate finding tCAI by minimizing the discrepancies between the Al-Mg and Pb-Pb chronometers. Assuming Δt26=ΔtPb, we find the implied t’CAI= tPb+Δt26, then define t*CAIas the weighted mean of the t’CAI. t*CAIis the best guess for the Pb-Pb age of t=0; the assumption of homogeneity is justified if the t’CAI cluster within errors around t*CAI. This statistical approach is similar to, but improves on, that of[9]. We find t*CAI= 4568.73 ± 0.16 Myr. Below we discuss our methodology and the implications of this age for CAIs, 1.4 Myr older than the reported and typically used age 4567.30±0.16 Myr. Methods: We base our estimate of t*CAIon five achondrites for which published (26Al/27Al)0and Pb-Pb ages exist: the quenched angrites D’Orbigny, Sahara 99555 (SAH 99555), and Northwest Africa (NWA) 1670; the pseudo-eucrite Asuka 881394; and the inner disk achondrite. All are “NC” (non-carbonaceous) achondrites that likely cooled quickly enough that the Al-Mg and Pb-Pb systems achieved isotopic closure simultaneously. We also considered the “CC” (carbonaceous chondrite-like) achondrites NWA 2796 and NWA 6704, butdo not include them in our fit. Al-Mg and Pb-Pb seem not to have closed simultaneously, possibly because formation in the outer disk from volatile-rich composition led to slower cooling. Of the 8 chondrules from NWA 5697 measured by [20,21], we also consider the 4 for which 238U/235U was measured: 2-C1, 5-C2, 3-C5, 11-C1.Depending on their post-formation thermal histories, the Al-Mg and Pb-Pb systems in chondrules may or may not have closed simultaneously. Table 1: (26Al/27Al)0, Pb-Pb ages of selected samplesSample(26Al/27Al)0/ 10-6RefPb-PbRefD’Orbigny3.98±0.15104563.43±0.19♮10-12SAH 995553.64±0.18104563.88±0.2712NWA16705.92±0.59104564.39±0.24*10Asuka 88139413.1±0.5613-154564.98±0.1715NWA 73253.03±0.14164563.4±2.616NWA 27963.94±0.16174562.89±0.5917NWA 67043.03±0.14184562.76±0.26192-C17.56±1.53204567.57±0.56*215-C27.04±1.51204567.54±0.52*213-C58.85±1.83204566.20±0.63*2111-C15.55±1.84204565.84±0.72*21*regression based on one subset of data points ♮weighted mean of two datasets Pb-Pb ages are proportional to the intercept of the line formed by linear regression of 207Pb/206Pb vs. 206Pb/204Pb data from various washes, leachates and residues of acid dissolution of a sample. Because contamination by terrestrial or primordial Pb is pervasive, some fractions must be excluded from regressions to ensure a fit with acceptable mean squares weighted deviation (MSWD). Usually points are excluded based on low [Pb], or low 206Pb/204Pb ratio(low radiogenic component), with single outliers identified [11,12,15,16,17]. In the starred examples (Table 1)and the case of 3 CAI Pb-Pb ages [5], up to half the points were excluded solely because did not fit a pre-determined line. This approach is vulnerable to confirmation bias and produces fits with low MSWD and too-low Pb-Pb age uncertainty. Regressing the same data points as [10], were produce the Pb-Pb age of NWA 1670 of 4564.39±0.24 Myr. But selecting other combinations of data points, other, equally valid, isochrons yield ages from 4563.77±0.21 Myr to 4564.64±0.23 Myr. Similar arguments apply to the Pb-Pb isochrons built by [21] for chondrules 2-C1 (we find 4567.33±0.44 to 4567.85±0.46 Myr), 5-C2 (4566.84±0.53 to 4567.70±0.44 Myr), 3-C5 (4565.84±0.54to 4567.04±0.54)and 11-C1 (4565.36±0.51 to 4565.74±0.45 Myr). Our adopted ages for these and NWA 1670 are listed in Table 2.Table 2. tCAI estimated from various components, using our regressions for the chondrules & NWA 1670.SampleΔt26(Myr)tPb(Myr)t’CAI(Myr)D’Orbigny5.05±0.044563.43±0.194568.48±0.19SAH 995555.14±0.054563.88±0.274569.02±0.27NWA16704.64±0.104564.21±0.634568.85±0.67Asuka 8813943.81±0.044564.98±0.174568.79±0.17NWA 73255.33±0.054563.4±2.64568.7±2.6NWA 27965.06±0.044562.89±0.594567.95±0.59NWA 67045.29±0.134562.76±0.264568.05±0.292-C12.00±0.214567.59±0.704569.59±0.725-C22.07±0.224567.23±0.914569.30±0.933-C51.84±0.214566.44±1.124568.28±1.1411-C12.32±0.344565.52±0.664567.84±0.73achondrite4568.72±0.16chondrules4568.76±0.58combined4568.73±0.16A weighted average of the five NC achondrites(or just D’Orbigny, SAH 99555 and Asuka 881394)yields t*CAI= 4568.72 ± 0.16Myr. All are consistent with this value to within 1.8σ, and MSWD=1.5. Including the 4 U-corrected chondrules, t*CAI= 4568.73± 0.16Myrwith MSWD=1.66, which is statistically significant. All chondrules and NC achondrites are consistent with this to within 1.8σ, (Figure 1).Figure 1. Al-Mg formation times after t=0 vs. Pb-Pb ages. The five NC achondrites and four chondrules are consistent with a Pb-Pb age of t=0 of 4568.7 Myr. Discussion: The data from achondrites and chondrules are consistent with a single Pb-Pb age at t=0, justifying the assumption of 26Al homogeneity. The age, 4568.7 Myr, is ≈1.4 Myr older than the commonly accepted Pb-Pb age of CAIs that formed with canonical 26Al/27Al at t=0 [3]. Others have interpreted the discrepancy to signify 26Al heterogeneity in the CAI-forming region[5,21]. We suggest instead that CAIs were exposed to transient heating events that reset the Pb-Pb system without disturbing the Al-Mg system. Notably, chondrules typically experienced transient heating at these times in the nebula [22]. If so, direct measurements of CAIs will not yield as reliable a Pb-Pb age of t=0 as statistical approaches like this and that of [9].References:[1] Auer et al. 2009. [2] Jacobsen, B et al. 2008, EPSL 272, 353-364. [3] Tissot, Fet al. 2017, GCA 213, 593-617.[4] Villa, I et al. 2016, GCA 172, 387-392.[5] Amelin, Y et al. 2010, EPSL 300, 343-350.[6] Connelly, Jet al. 2012, Science 338, 651.[7] Bouvier, Aet al. 2011, LPICo 1639, 9054. [8] Bouvier, Aand Wadhwa, M2010, Nat Geosci 3, 637-641.[9] Nyquist, Let al. 2009, GCA 73, 5115-5136.[10] Schiller et al. 2015. [11] Wadhwa & Brennecka 2012. [12] Tissot et al. 2017. [13] Nyquist et al. 2003. [14] Wadhwa et al. 2009. [15] Wimpenny et al. 2019, GCA 244, 478-501.[16] Koefoed et al. 2016, GCA 183, 31-45. [17] Bouvier, A et al. 2011, GCA 75, 5310-5323. [18] Sanborn, Met al. 2019, GCA 245, 577-596. [19] Amelin, Yet al. 2019, GCA 245, 628-642.[20] Bollard, Jet al. 2017, Sci Adv 3 ,e1700407. [21] Bollard, Jet al. 2019, GCA 260, 62-83.[22] Villeneuve, J et al. 2009, Science 325, 985

S. J. Desch↗
DOE OSTI2020

Materials Data on Mg(FeO2)2 by Materials Project

MgFe2O4 is Spinel-like structured and crystallizes in the monoclinic Cm space group. The structure is three-dimensional. there are six inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to four O2- atoms to form MgO4 tetrahedra that share corners with three MgO6 octahedra and corners with nine FeO6 octahedra. The corner-sharing octahedra tilt angles range from 56–59°. There are a spread of Mg–O bond distances ranging from 1.99–2.02 Å. In the second Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with six FeO4 tetrahedra, edges with two MgO6 octahedra, and edges with four FeO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.09–2.11 Å. In the third Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with two equivalent MgO4 tetrahedra, corners with four FeO4 tetrahedra, an edgeedge with one MgO6 octahedra, and edges with five FeO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.08–2.11 Å. In the fourth Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with six FeO4 tetrahedra, edges with two MgO6 octahedra, and edges with four FeO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.09–2.11 Å. In the fifth Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with six FeO4 tetrahedra, edges with two MgO6 octahedra, and edges with four equivalent FeO6 octahedra. There are five shorter (2.09 Å) and one longer (2.10 Å) Mg–O bond lengths. In the sixth Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share a cornercorner with one MgO4 tetrahedra, corners with five FeO4 tetrahedra, an edgeedge with one MgO6 octahedra, and edges with five FeO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.07–2.10 Å. There are nine inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with two equivalent MgO4 tetrahedra, corners with four FeO4 tetrahedra, edges with three MgO6 octahedra, and edges with three FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.01–2.09 Å. In the second Fe3+ site, Fe3+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with six MgO6 octahedra and corners with six FeO6 octahedra. The corner-sharing octahedra tilt angles range from 56–57°. There are a spread of Fe–O bond distances ranging from 1.91–1.97 Å. In the third Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with three equivalent MgO4 tetrahedra, corners with three equivalent FeO4 tetrahedra, edges with two MgO6 octahedra, and edges with four FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 1.99–2.10 Å. In the fourth Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six FeO4 tetrahedra, edges with two equivalent FeO6 octahedra, and edges with four MgO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.03–2.07 Å. In the fifth Fe3+ site, Fe3+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with six MgO6 octahedra and corners with six FeO6 octahedra. The corner-sharing octahedra tilt angles range from 56–57°. There are a spread of Fe–O bond distances ranging from 1.91–1.96 Å. In the sixth Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share a cornercorner with one MgO4 tetrahedra, corners with five FeO4 tetrahedra, edges with three MgO6 octahedra, and edges with three FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.00–2.10 Å. In the seventh Fe3+ site, Fe3+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with six MgO6 octahedra and corners with six FeO6 octahedra. The corner-sharing octahedral tilt angles are 57°. There is two shorter (1.91 Å) and two longer (1.97 Å) Fe–O bond length. In the eighth Fe3+ site, Fe3+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with six MgO6 octahedra and corners with six FeO6 octahedra. The corner-sharing octahedra tilt angles range from 57–58°. There is two shorter (1.91 Å) and two longer (1.97 Å) Fe–O bond length. In the ninth Fe3+ site, Fe3+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with three MgO6 octahedra and corners with nine FeO6 octahedra. The corner-sharing octahedra tilt angles range from 56–58°. There is three shorter (1.93 Å) and one longer (1.98 Å) Fe–O bond length. There are eighteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a rectangular see-saw-like geometry to two Mg2+ and two Fe3+ atoms. In the second O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Fe3+ atoms. In the third O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Fe3+ atoms. In the fourth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Mg2+ and two Fe3+ atoms. In the fifth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Fe3+ atoms. In the sixth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Fe3+ atoms. In the seventh O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Mg2+ and two Fe3+ atoms. In the eighth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Fe3+ atoms. In the ninth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Fe3+ atoms. In the tenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to two Mg2+ and two Fe3+ atoms. In the eleventh O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Fe3+ atoms. In the twelfth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Mg2+ and two Fe3+ atoms. In the thirteenth O2- site, O2- is bonded to two Mg2+ and two equivalent Fe3+ atoms to form distorted corner-sharing OMg2Fe2 trigonal pyramids. In the fourteenth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Fe3+ atoms. In the fifteenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Mg2+ and three Fe3+ atoms. In the sixteenth O2- site, O2- is bonded to four Fe3+ atoms to form distorted OFe4 trigonal pyramids that share corners with four OMg2Fe2 trigonal pyramids and edges with three OMgFe3 trigonal pyramids. In the seventeenth O2- site, O2- is bonded to one Mg2+ and three Fe3+ atoms to form distorted OMgFe3 trigonal pyramids that share corners with four OMg2Fe2 trigonal pyramids and edges with three OFe4 trigonal pyramids. In the eighteenth O2- site, O2- is bonded to one Mg2+ and three Fe3+ atoms to form distorted OMgFe3 trigonal pyramids that share corners with three equivalent OMg2Fe2 trigonal pyramids and edges with three OFe4 trigonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg(ClO3)2 by Materials Project

Mg(O3Cl)2 crystallizes in the monoclinic C2/m space group. The structure is one-dimensional and consists of two Mg(O3Cl)2 ribbons oriented in the (0, 0, 1) direction. Mg is bonded in an octahedral geometry to six O atoms. There are two shorter (2.02 Å) and four longer (2.16 Å) Mg–O bond lengths. There are two inequivalent O sites. In the first O site, O is bonded in a 2-coordinate geometry to one Mg and one O atom. The O–O bond length is 1.28 Å. In the second O site, O is bonded in a bent 120 degrees geometry to one Mg and one Cl atom. The O–Cl bond length is 1.62 Å. Cl is bonded in a single-bond geometry to one O atom.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Synthesis and Mg 2+ deintercalation in manganese spinel nanocrystals

Transition metal oxides are promising materials as cathodes for divalent batteries with high capacity under high voltage. A major challenge is the sluggish kinetics of intercalation of divalent cations into the oxide host. Tailoring of the size, composition and crystal structure of oxides is a necessary strategy to alleviate these barriers, which challenges our control of their synthesis. In this work, we selectively synthesize spinel-type Mg x Mn 3-x O 4 nanocrystals with different Mg/Mn ratios and investigate their ability to electrochemically shuttle Mg 2+ ions. Crystal-chemical characterization of the reaction outcomes was conducted with X-ray diffraction, X-ray absorption spectroscopy, electron microscopy, and elemental analysis. Both 5 nm thick MgMn 2 O 4 nanosheets and 10 nm Mg 0.41 Mn 2.59 O 4 nanocubes underwent reversible Mg 2+ deintercalation, yet no obvious reaction was observed in 60 nm Mg 1.2 Mn 1.8 O 4 nanocubes. Our results suggest that both the size of the spinel nanocrystals and the Mg/Mn ratios play a role in the observed behaviour. The advances in the synthesis of spinel oxide nanocrystals achieved, and their correlation with Mg 2+ deintercalation, pave the way toward the precise synthesis of multivalent cathode materials that fundamentally overcome barriers to practical application.

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

Coexisting normal and intruder configurations in 32 Mg

Situated in the so-called “island of inversion,” the nucleus 32 Mg is considered as an archetypal example of the disappearance of magicity at N = 20. We report on high statistics in-beam spectroscopy of 32 Mg with a unique approach, in that two direct reaction probes with different sensitivities to the underlying nuclear structure are employed at the same time. More specifically, states in 32 Mg were populated by knockout reactions starting from 33 Mg and 34 Si, lying inside and outside the island of inversion, respectively. The momentum distributions of the reaction residues and the cross sections leading to the individual final states were confronted with eikonal-based reaction calculations, yielding a significantly updated level scheme for 32 Mg and spin-parity assignments. By fully exploiting observables obtained in this measurement, a variety of structures coexisting in 32 Mg was unraveled. Comparisons with theoretical predictions based on shell-model overlaps allowed for clear discrimination between different structural models, revealing that the complete theoretical description of this key nucleus is yet to be achieved.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Nanoscale Mg–B via Surfactant Ball Milling of MgB 2 : Morphology, Composition, and Improved Hydrogen Storage Properties

Metal borides have attracted the attention of researchers due to their useful physical properties and unique ability to form high hydrogen-capacity metal borohydrides. We demonstrate improved hydrogen storage properties of a nanoscale Mg–B material made by surfactant ball milling MgB 2 in a mixture of heptane, oleic acid, and oleylamine. Transmission electron microscopy data show that Mg–B nanoplatelets are produced with sizes ranging from 5 to 50 nm, which agglomerate upon ethanol washing to produce an agglomerated nanoscale Mg–B material of micron-sized particles with some surfactant still remaining. X-ray diffraction measurements reveal a two-component material where 32% of the solid is a strained crystalline solid maintaining the hexagonal structure with the remainder being amorphous. Fourier transform infrared shows that the oleate binds in a “bridge-bonding” fashion preferentially to magnesium rather than boron, which is confirmed by density functional theory calculations. The Mg–B nanoscale material is deficient in boron relative to bulk MgB 2 with a Mg–B ratio of ~1:0.75. The nanoscale MgB 0.75 material has a disrupted B–B ring network as indicated by X-ray absorption measurements. Hydrogenation experiments at 700 bar and 280 °C show that it partially hydrogenates at temperatures 100 °C below the threshold for bulk MgB 2 hydrogenation. In addition, upon heating to 200 °C, the H–H bond-breaking ability increases ~10-fold according to hydrogen–deuterium exchange experiments due to desorption of oleate at the surface. This behavior would make the nanoscale Mg–B material useful as an additive where rapid H–H bond breaking is needed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

First-Principles Elucidation of Initial Dehydrogenation Pathways in Mg(BH 4 ) 2

Complex borohydrides such as Mg(BH 4 ) 2 offer one of highest capacities to chemically store hydrogen for onboard applications; however, it suffers greatly from kinetic constraints that prevent realization of full capacity and reversibility. Understanding these kinetic limitations solely from experiments is extremely challenging due to the unusual complexity of various competing elemental reaction steps involved during the de/rehydrogenation reaction. This work aims to map out the energetics associated with initial dehydrogenation of Mg(BH 4 ) 2 from first-principles simulations and to identify the preferred reaction pathways. Our calculations suggest the rate-limiting step during BH 4 – –B 3 H 8 – conversion is the formation of the B 2 H 7 – intermediate. We further emphasize and clarify that the B 3 H 8 – and H – intermediates, formed during initial Mg(BH 4 ) 2 decomposition, appear as molecular species that are embedded in the Mg–BH 4 –Mg matrix as evidenced in the nuclear magnetic resonance measurements and not as bulk MgH 2 and Mg(B 3 H 8 ) 2 as previously assumed in theoretical predictions of the thermodynamics.

08 HYDROGEN↗
DOE OSTI2020

High Capacity for Mg 2+ Deintercalation in Spinel Vanadium Oxide Nanocrystals

Nonaqueous Mg batteries can theoretically reach high energy density with cost-effective materials, yet no such device to date has performance competitive with Li-ion technologies. A major barrier is the need for oxide cathodes that combine high capacity and voltage. Very few oxides have shown intrinsic ability for Mg 2+ intercalation in electrolytes with acceptably low content of H2O. Herein, we demonstrate that nanocrystals of MgV 2 O 4 can reach high capacity for Mg 2+ deintercalation with a mechanism that preserves their spinel framework, validated through measurements with different chemical and structural sensitivity. The structural stability contrasts with other phases where reaching high capacity required distortions that introduce undesirable mechanical strain. The favorable properties of the oxide allowed cycling in a full cell with Mg metal. This work reveals new insights into the viability of multivalent intercalation in oxides, meeting a milestone toward the feasibility of high-voltage batteries with either Mg metal or Mg-ion anodes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Cation Disorder of ${\text{Mg}}_{\mathbf{2}}{\text{SiO}}_{\mathbf{4}}$ in Super‐Earth Mantles

Understanding the mineralogy of exoplanets is essential for unraveling their interior structures, dynamics, and evolution. For large super-Earths, the post-post spinel ${\text{Mg}}_{\mathbf{2}}{\text{SiO}}_{\mathbf{4}}$, one of the major mantle phases, may undergo the order-disorder transition (ODT) at high temperatures. However, the ODT phase boundary of ${\text{Mg}}_{\mathbf{2}}{\text{SiO}}_{\mathbf{4}}$ has not been rigorously constrained. Additionally, fundamental thermodynamic properties of the disordered ${\text{Mg}}_{\mathbf{2}}{\text{SiO}}_{\mathbf{4}}$ remain poorly investigated. Here, we develop a unified machine learning potential (MLP) for ${\text{Mg}}_{\mathbf{2}}{\text{SiO}}_{\mathbf{4}}$ of ab initio accuracy under super-Earth mantle conditions. With the efficient MLP, we extensively calculate the free energy of post-post spinel ${\text{Mg}}_{\mathbf{2}}{\text{SiO}}_{\mathbf{4}}$ via the thermodynamic integration method. The results are used to constrain the ODT phase boundary. Furthermore, we report the P-V-T equation of state and Grüneisen parameters for post-post spinel ${\text{Mg}}_{\mathbf{2}}{\text{SiO}}_{\mathbf{4}}$ across various degrees of disorder. These thermodynamic properties are further applied to update the adiabatic thermal profiles and the mass-radius relation of super-Earths.

36 MATERIALS SCIENCE↗
DOE OSTI2021

High Mg activation in implanted GaN by high temperature and ultrahigh pressure annealing

Not provided.We demonstrate high p-type conductivity and hole concentrations >10 18 cm -3 in Mg-implanted GaN. The implantation was performed at room temperature and by post-implantation annealing at 1 GPa of N 2 and in a temperature range of 1200–1400 °C. The high pressure thermodynamically stabilized the GaN surface without the need of a capping layer. We introduce a “diffusion budget,” related to the diffusion length, as a convenient engineering parameter for comparing samples annealed at different temperatures and for different times. Although damage recovery, as measured by XRD, was achieved at relatively low diffusion budgets, these samples did not show p-type conductivity. Further analyses showed heavy compensation by the implantation-induced defects. Higher diffusion budgets resulted in a low Mg ionization energy (~115 meV) and almost complete Mg activation. For even higher diffusion budgets, we observed significant loss of Mg to the surface and a commensurate reduction in the hole conductivity. High compensation at low diffusion budgets and loss of Mg at high diffusion budgets present a unique challenge for shallow implants. A direct control of the formation of compensating defects arising from the implantation damage may be necessary to achieve both hole conductivity and low Mg diffusion.

36 MATERIALS SCIENCE↗
DOE OSTI2022

β -Ga 2 O 3 MESFETs with insulating Mg-doped buffer grown by plasma-assisted molecular beam epitaxy

In this work, we develop in situ Mg doping techniques in plasma-assisted molecular beam epitaxy (PAMBE) of β -Ga 2 O 3 to compensate Si dopants at the substrate epilayer growth interface and eliminate parasitic leakage paths. Both abrupt and uniform Mg doping profiles over a wide range of concentrations were achieved in β -Ga 2 O 3 epilayers grown by PAMBE. Capacitance–voltage characteristics of Si and Mg co-doped samples confirmed the compensating effect of the Mg dopants. Mg delta-doping was then integrated into a β -Ga 2 O 3 metal-semiconductor field effect transistor structure and shown to be effective in eliminating source leakage. In conclusion, the results presented here show that Mg doping is a promising way to engineer insulating buffer layers for β -Ga 2 O 3 lateral devices grown by PAMBE.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Dissolution of Mg-enriched defects in implanted GaN and increased p-type dopant activation

Annealing Mg-implanted homoepitaxial GaN at temperatures above 1400 °C eliminates the formation of inversion domains and leads to improved dopant activation efficiency. Extended defects, in the form of inversion domains, contain electrically inactive Mg after post-implantation annealing at temperatures as high as 1300 °C (one GPa N 2 overpressure), which results in a low dopant activation efficiency. Triple-axis x-ray data reveal that implant-induced strain is fully relieved after annealing at 1300 °C for 10 min, indicating that strain-inducing point defects formed during implantation have reconfigured and inversion domains are formed. However, annealing at temperatures of 1400–1500 °C (one GPa N 2 overpressure) eliminates the presence of the inversion domains. While residual defects, such as dislocation loops, still exist after annealing at and above 1400 °C, chemical analysis at multiple dislocation loops shows no sign of Mg segregation. Meanwhile, an overall decreasing trend in the dislocation loop density is observed after annealing at the higher temperatures and longer times. Additionally, once inversion domains are formed and the samples are cooled to room temperature, they are shown to dissolve with subsequent annealing above 1400 °C. While such defects have been observed before, the important finding that such defects can be dissolved with a short, higher temperature step is key. Earlier work [Breckenridge et al., J. Appl. Phys. Lett. 118, 022101 (2021)] addressing electrical measurements of these types of samples showed that annealing at 1400 °C leads to a dopant activation efficiency that is an order of magnitude higher than that observed at 1300 °C. In conclusion, this work complements earlier work by identifying the inversion domains, which incorporate Mg, and points to the benefits, in terms of defect density and p-type dopant activation, of using higher temperature (>1400 °C) annealing cycles to activate Mg in GaN, even if the Mg-containing inversion domains had been formed during lower temperature annealing.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Mg and native defects in cubic silicon carbide from first principles

The diffusion of Mg defects in 3C-SiC is studied using the density functional theory. Mg has the highest burn-in rate as a transmutant in 3C-SiC when it is placed in high-energy neutron irradiation environment of a fusion reactor. The presence and evolution of transmutant defects impact thermal and mechanical properties of this important structural material. This study is focused on understanding the structure, stability, and evolution of Mg defects and the interaction of Mg with native defects in 3C-SiC. Our calculations of diffusion coefficients for different Mg defects suggest that Mg is likely to diffuse faster in pristine 3C-SiC than in the damaged one, in agreement with earlier experimental observations.

36 MATERIALS SCIENCE↗