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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on VIr by Materials Project

IrV is beta-prime cadmium gold-like structured and crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. there are six inequivalent V sites. In the first V site, V is bonded in a 12-coordinate geometry to one V and eight Ir atoms. The V–V bond length is 2.54 Å. There are a spread of V–Ir bond distances ranging from 2.59–2.71 Å. In the second V site, V is bonded in a 12-coordinate geometry to one V and eight Ir atoms. The V–V bond length is 2.57 Å. There are a spread of V–Ir bond distances ranging from 2.65–2.73 Å. In the third V site, V is bonded in a body-centered cubic geometry to eight Ir atoms. There are four shorter (2.55 Å) and four longer (2.60 Å) V–Ir bond lengths. In the fourth V site, V is bonded in a 8-coordinate geometry to eight Ir atoms. There are four shorter (2.60 Å) and four longer (2.64 Å) V–Ir bond lengths. In the fifth V site, V is bonded to four V and eight Ir atoms to form a mixture of distorted corner and face-sharing VV4Ir8 cuboctahedra. There are one shorter (2.78 Å) and one longer (2.90 Å) V–V bond lengths. All V–Ir bond lengths are 2.74 Å. In the sixth V site, V is bonded to four V and eight Ir atoms to form a mixture of distorted corner and face-sharing VV4Ir8 cuboctahedra. The V–V bond length is 2.68 Å. There are four shorter (2.79 Å) and four longer (2.80 Å) V–Ir bond lengths. There are three inequivalent Ir sites. In the first Ir site, Ir is bonded in a 8-coordinate geometry to eight V atoms. In the second Ir site, Ir is bonded in a 12-coordinate geometry to eight V atoms. In the third Ir site, Ir is bonded in a 8-coordinate geometry to eight V atoms.

36 MATERIALS SCIENCE↗
NASA NTRS1995

Near-infrared spectra of compact stellar wind sources at the Galactic center

We present high- and low-resolution, H- and K-band spectra on nine compact 2.2 micrometers Galactic center sources in which we clearly detect He I 2.058 micrometers emission, including the AF source, IRS 13, IRS 1W, IRS 16NE, IRS 16NW, IRS 16C, IRS 16SW, IRS 34, and IRS 6E. We have also obtained comparison spectra of both a luminous blue variable (LBV) and a WR star (P Cygni and HD 192163, respectively). Our H- and K-band spectrum of the LBV P Cygni strongly resembles the near-infrared spectra of known WN9/Ofpe stars. Our spectra of the Galactic center sources share many characteristics in common with our spectrum of P Cygni. The spectra all show emission lines of H I and He I with large He I/H line flux ratios. Some have permitted and forbidden lines of Fe II. Brackett line widths and ratios indicate the presence of strong stellar winds. In contrast to the spectrum of the WR star, none of the Galactic center sources show evidence of He II emission lines in their spectra, suggesting that none of the Galactic center sources are WR stars. Our high-resolution H-band spectrum of the AF source differs from previously published low-resolution H-band spectra in that it is rich in emission lines. Furthermore, we find two distinct spectral components to the AF source separated in space by a few arcseconds. We identify both the emission-line component of the AF source and an exciting source of IRS 13 as an LBV or WN9/Ofpe star. Our results, when combined with the results of others, also suggest that IRS 16NE, IRS 16C, IRS 16NW, IRS 34, and a component of IRS 6E are early-type, emission-line stars. The argument for IRS 16SW, however, is less compelling. We find no evidence for a compact He I emission-line source at IRS 1W. This result contradicts previous findings, suggesting that the He I source at IRS 1W may be variable. If the He I lines in IRS 1W are truly variable, a stellar component of IRS 1W may be an LBV, because LBVs are known to have variable line emission on short timescales. The nine Galactic center wind sources appear to contribute a significant fraction of the total luminosity of the central few parsecs of the Galaxy.

Libonate, S.↗
DOE OSTI2020

Materials Data on La2Sb4Ir3 by Materials Project

La2Ir3Sb4 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent La sites. In the first La site, La is bonded in a 1-coordinate geometry to eight Ir and nine Sb atoms. There are a spread of La–Ir bond distances ranging from 3.25–3.71 Å. There are a spread of La–Sb bond distances ranging from 3.37–3.90 Å. In the second La site, La is bonded in a 8-coordinate geometry to six Ir and nine Sb atoms. There are a spread of La–Ir bond distances ranging from 3.33–3.63 Å. There are a spread of La–Sb bond distances ranging from 3.30–3.83 Å. There are three inequivalent Ir sites. In the first Ir site, Ir is bonded in a 10-coordinate geometry to five La and five Sb atoms. There are a spread of Ir–Sb bond distances ranging from 2.65–2.76 Å. In the second Ir site, Ir is bonded in a 10-coordinate geometry to four La and four Sb atoms. There are a spread of Ir–Sb bond distances ranging from 2.62–2.67 Å. In the third Ir site, Ir is bonded in a 5-coordinate geometry to five La and five Sb atoms. There are a spread of Ir–Sb bond distances ranging from 2.61–2.70 Å. There are four inequivalent Sb sites. In the first Sb site, Sb is bonded in a 3-coordinate geometry to five La and three Ir atoms. In the second Sb site, Sb is bonded in a 7-coordinate geometry to four La and three Ir atoms. In the third Sb site, Sb is bonded in a 6-coordinate geometry to five La and four Ir atoms. In the fourth Sb site, Sb is bonded in a 8-coordinate geometry to four La and four Ir atoms.

36 MATERIALS SCIENCE↗
NASA NTRS2015

On Infrared Excesses Associated with Li-Rich K Giants

Infrared (IR) excesses around K-type red giants (RGs) have previously been discovered using Infrared Astronomy Satellite (IRAS) data, and past studies have suggested a link between RGs with overabundant lithium and IR excesses, implying the ejection of circumstellar shells or disks. We revisit the question of IR excesses around RGs using higher spatial resolution IR data, primarily from the Wide-field Infrared Survey Explorer. Our goal was to elucidate the link between three unusual RG properties: fast rotation, enriched lithium, and IR excess. Our sample of RGs includes those with previous IR detections, a sample with well-defined rotation and lithium abundance measurements with no previous IR measurements, and a large sample of RGs asserted to be lithium-rich in the literature; we have 316 targets thought to be K giants, about 40% of which we take to be Li-rich. In 24 cases with previous detections of IR excess at low spatial resolution, we believe that source confusion is playing a role, in that either (a) the source that is bright in the optical is not responsible for the IR flux, or (b) there is more than one source responsible for the IR flux as measured in IRAS. We looked for IR excesses in the remaining sources, identifying 28 that have significant IR excesses by approximately 20 micrometers (with possible excesses for 2 additional sources). There appears to be an intriguing correlation in that the largest IR excesses are all in Li-rich K giants, though very few lithium-rich K giants have IR excesses (large or small). These largest IR excesses also tend to be found in the fastest rotators. There is no correlation of IR excess with the carbon isotopic ratio, 12C/13C. IR excesses by 20 micrometers, though relatively rare, are at least twice as common among our sample of lithium-rich K giants. If dust shell production is a common by-product of Li enrichment mechanisms, these observations suggest that the IR excess stage is very short-lived, which is supported by theoretical calculations. Conversely, the lithium-enrichment mechanism may only occasionally produce dust, and an additional parameter (e.g., rotation) may control whether or not a shell is ejected.

Li-rich↗
DOE OSTI2020

Materials Data on Ce5Ir4 by Materials Project

Ce5Ir4 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are three inequivalent Ce sites. In the first Ce site, Ce is bonded in a 7-coordinate geometry to seven Ir atoms. There are a spread of Ce–Ir bond distances ranging from 2.89–3.33 Å. In the second Ce site, Ce is bonded to six Ir atoms to form distorted corner-sharing CeIr6 octahedra. The corner-sharing octahedra tilt angles range from 49–52°. There are a spread of Ce–Ir bond distances ranging from 2.74–3.21 Å. In the third Ce site, Ce is bonded in a 6-coordinate geometry to six Ir atoms. There are a spread of Ce–Ir bond distances ranging from 2.81–3.02 Å. There are three inequivalent Ir sites. In the first Ir site, Ir is bonded in a 9-coordinate geometry to eight Ce and one Ir atom. The Ir–Ir bond length is 2.80 Å. In the second Ir site, Ir is bonded in a 8-coordinate geometry to eight Ce atoms. In the third Ir site, Ir is bonded in a 9-coordinate geometry to eight Ce and one Ir atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on UIr by Materials Project

UIr crystallizes in the monoclinic P2_1 space group. The structure is three-dimensional. there are four inequivalent U sites. In the first U site, U is bonded in a 7-coordinate geometry to seven Ir atoms. There are a spread of U–Ir bond distances ranging from 2.79–3.06 Å. In the second U site, U is bonded in a 5-coordinate geometry to six Ir atoms. There are a spread of U–Ir bond distances ranging from 2.80–3.18 Å. In the third U site, U is bonded in a 7-coordinate geometry to seven Ir atoms. There are a spread of U–Ir bond distances ranging from 2.81–3.05 Å. In the fourth U site, U is bonded in a 5-coordinate geometry to seven Ir atoms. There are a spread of U–Ir bond distances ranging from 2.81–3.23 Å. There are four inequivalent Ir sites. In the first Ir site, Ir is bonded in a 7-coordinate geometry to seven U atoms. In the second Ir site, Ir is bonded in a 5-coordinate geometry to six U atoms. In the third Ir site, Ir is bonded in a 7-coordinate geometry to seven U atoms. In the fourth Ir site, Ir is bonded in a 5-coordinate geometry to seven U atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on VIr by Materials Project

IrV is beta-prime cadmium gold-like structured and crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. there are four inequivalent V sites. In the first V site, V is bonded in a 8-coordinate geometry to one V and eight Ir atoms. The V–V bond length is 2.62 Å. There are a spread of V–Ir bond distances ranging from 2.62–2.73 Å. In the second V site, V is bonded in a distorted body-centered cubic geometry to eight Ir atoms. There are a spread of V–Ir bond distances ranging from 2.57–2.66 Å. In the third V site, V is bonded to four V and eight Ir atoms to form a mixture of distorted corner and face-sharing VV4Ir8 cuboctahedra. There are a spread of V–V bond distances ranging from 2.55–2.77 Å. There are a spread of V–Ir bond distances ranging from 2.69–2.79 Å. In the fourth V site, V is bonded in a 12-coordinate geometry to two equivalent V and eight Ir atoms. There are a spread of V–Ir bond distances ranging from 2.61–2.74 Å. There are four inequivalent Ir sites. In the first Ir site, Ir is bonded in a 8-coordinate geometry to eight V atoms. In the second Ir site, Ir is bonded in a 12-coordinate geometry to eight V atoms. In the third Ir site, Ir is bonded in a 8-coordinate geometry to eight V atoms. In the fourth Ir site, Ir is bonded in a 8-coordinate geometry to eight V atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on FeIr by Materials Project

FeIr crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are three inequivalent Fe sites. In the first Fe site, Fe is bonded to six equivalent Fe and six equivalent Ir atoms to form distorted FeFe6Ir6 cuboctahedra that share corners with twelve FeFe6Ir6 cuboctahedra, edges with twelve FeFe6Ir6 cuboctahedra, edges with twelve equivalent IrFe6Ir6 cuboctahedra, faces with six equivalent FeFe6Ir6 cuboctahedra, and faces with twelve equivalent IrFe6Ir6 cuboctahedra. All Fe–Fe bond lengths are 2.64 Å. All Fe–Ir bond lengths are 2.59 Å. In the second Fe site, Fe is bonded to six equivalent Fe and six Ir atoms to form distorted FeFe6Ir6 cuboctahedra that share corners with five equivalent IrFe6Ir10 cuboctahedra, corners with twelve FeFe6Ir6 cuboctahedra, edges with ten IrFe6Ir6 cuboctahedra, edges with twelve FeFe6Ir6 cuboctahedra, faces with six equivalent FeFe6Ir6 cuboctahedra, and faces with fifteen IrFe6Ir6 cuboctahedra. All Fe–Fe bond lengths are 2.64 Å. All Fe–Ir bond lengths are 2.59 Å. In the third Fe site, Fe is bonded to six equivalent Fe and six Ir atoms to form distorted FeFe6Ir6 cuboctahedra that share corners with five equivalent IrFe6Ir10 cuboctahedra, corners with twelve FeFe6Ir6 cuboctahedra, edges with ten IrFe6Ir6 cuboctahedra, edges with twelve FeFe6Ir6 cuboctahedra, faces with six equivalent FeFe6Ir6 cuboctahedra, and faces with fifteen IrFe6Ir6 cuboctahedra. All Fe–Fe bond lengths are 2.64 Å. All Fe–Ir bond lengths are 2.59 Å. There are two inequivalent Ir sites. In the first Ir site, Ir is bonded to six Fe and six equivalent Ir atoms to form distorted IrFe6Ir6 cuboctahedra that share corners with twelve IrFe6Ir6 cuboctahedra, edges with twelve FeFe6Ir6 cuboctahedra, edges with twelve IrFe6Ir6 cuboctahedra, faces with six equivalent IrFe6Ir6 cuboctahedra, and faces with twelve FeFe6Ir6 cuboctahedra. All Ir–Ir bond lengths are 2.64 Å. In the second Ir site, Ir is bonded to six Fe and ten equivalent Ir atoms to form distorted IrFe6Ir10 cuboctahedra that share corners with ten FeFe6Ir6 cuboctahedra, corners with twelve IrFe6Ir6 cuboctahedra, edges with eight FeFe6Ir6 cuboctahedra, edges with sixteen IrFe6Ir6 cuboctahedra, faces with sixteen equivalent IrFe6Ir10 cuboctahedra, and faces with eighteen FeFe6Ir6 cuboctahedra. There are a spread of Ir–Ir bond distances ranging from 2.64–5.28 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zr5Ir2Os by Materials Project

Zr5OsIr2 crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. there are five inequivalent Zr sites. In the first Zr site, Zr is bonded in a 6-coordinate geometry to two equivalent Os and four Ir atoms. Both Zr–Os bond lengths are 2.82 Å. There are three shorter (2.83 Å) and one longer (2.84 Å) Zr–Ir bond lengths. In the second Zr site, Zr is bonded in a 5-coordinate geometry to two equivalent Os and three Ir atoms. There are one shorter (2.78 Å) and one longer (2.88 Å) Zr–Os bond lengths. There are one shorter (2.84 Å) and two longer (3.07 Å) Zr–Ir bond lengths. In the third Zr site, Zr is bonded in a 5-coordinate geometry to two equivalent Os and three Ir atoms. Both Zr–Os bond lengths are 2.82 Å. There are one shorter (2.90 Å) and two longer (3.07 Å) Zr–Ir bond lengths. In the fourth Zr site, Zr is bonded in a 5-coordinate geometry to two equivalent Os and three Ir atoms. Both Zr–Os bond lengths are 3.08 Å. There are a spread of Zr–Ir bond distances ranging from 2.80–2.90 Å. In the fifth Zr site, Zr is bonded in a 5-coordinate geometry to five Ir atoms. There are a spread of Zr–Ir bond distances ranging from 2.80–3.06 Å. Os is bonded in a 9-coordinate geometry to nine Zr atoms. There are three inequivalent Ir sites. In the first Ir site, Ir is bonded in a 9-coordinate geometry to nine Zr atoms. In the second Ir site, Ir is bonded in a 9-coordinate geometry to nine Zr atoms. In the third Ir site, Ir is bonded in a 9-coordinate geometry to nine Zr atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg2BeB2Ir5 by Materials Project

Mg2BeIr5B2 crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. there are two inequivalent Mg sites. In the first Mg site, Mg is bonded in a 11-coordinate geometry to two equivalent Mg, ten Ir, and three B atoms. Both Mg–Mg bond lengths are 2.90 Å. There are a spread of Mg–Ir bond distances ranging from 2.74–2.91 Å. There are one shorter (2.54 Å) and two longer (2.88 Å) Mg–B bond lengths. In the second Mg site, Mg is bonded in a 11-coordinate geometry to two equivalent Mg, ten Ir, and three B atoms. Both Mg–Mg bond lengths are 2.90 Å. There are a spread of Mg–Ir bond distances ranging from 2.74–2.91 Å. There are one shorter (2.54 Å) and two longer (2.88 Å) Mg–B bond lengths. Be is bonded in a body-centered cubic geometry to eight equivalent Ir atoms. All Be–Ir bond lengths are 2.49 Å. There are two inequivalent Ir sites. In the first Ir site, Ir is bonded in a distorted body-centered cubic geometry to four equivalent Mg and four equivalent B atoms. All Ir–B bond lengths are 2.24 Å. In the second Ir site, Ir is bonded in a 8-coordinate geometry to four equivalent Mg, two equivalent Be, and two equivalent B atoms. Both Ir–B bond lengths are 2.17 Å. There are two inequivalent B sites. In the first B site, B is bonded in a 7-coordinate geometry to three equivalent Mg and six Ir atoms. All B–Ir bond lengths are 2.17 Å. In the second B site, B is bonded in a 7-coordinate geometry to three Mg and six Ir atoms. Both B–Ir bond lengths are 2.24 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg2VB2Ir5 by Materials Project

Mg2VIr5B2 crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. there are two inequivalent Mg sites. In the first Mg site, Mg is bonded in a 11-coordinate geometry to two equivalent Mg, ten Ir, and three B atoms. Both Mg–Mg bond lengths are 2.92 Å. There are a spread of Mg–Ir bond distances ranging from 2.78–2.97 Å. There are one shorter (2.69 Å) and two longer (2.89 Å) Mg–B bond lengths. In the second Mg site, Mg is bonded in a 11-coordinate geometry to two equivalent Mg, ten Ir, and three B atoms. Both Mg–Mg bond lengths are 2.92 Å. There are a spread of Mg–Ir bond distances ranging from 2.78–2.97 Å. There are one shorter (2.69 Å) and two longer (2.89 Å) Mg–B bond lengths. V is bonded in a body-centered cubic geometry to eight equivalent Ir atoms. All V–Ir bond lengths are 2.60 Å. There are two inequivalent Ir sites. In the first Ir site, Ir is bonded in a distorted body-centered cubic geometry to four equivalent Mg and four equivalent B atoms. All Ir–B bond lengths are 2.22 Å. In the second Ir site, Ir is bonded in a 8-coordinate geometry to four Mg, two equivalent V, and two equivalent B atoms. Both Ir–B bond lengths are 2.18 Å. There are two inequivalent B sites. In the first B site, B is bonded in a 7-coordinate geometry to three Mg and six Ir atoms. All B–Ir bond lengths are 2.18 Å. In the second B site, B is bonded in a 7-coordinate geometry to three Mg and six Ir atoms. Both B–Ir bond lengths are 2.22 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca2P7Ir12 by Materials Project

Ca2Ir12P7 crystallizes in the trigonal P-3 space group. The structure is three-dimensional. Ca is bonded to twelve Ir and six equivalent P atoms to form distorted CaP6Ir12 cuboctahedra that share corners with three equivalent PIr6 octahedra, edges with six equivalent CaP6Ir12 cuboctahedra, and faces with two equivalent CaP6Ir12 cuboctahedra. The corner-sharing octahedral tilt angles are 27°. There are a spread of Ca–Ir bond distances ranging from 3.08–3.41 Å. There are three shorter (3.00 Å) and three longer (3.02 Å) Ca–P bond lengths. There are two inequivalent Ir sites. In the first Ir site, Ir is bonded in a 4-coordinate geometry to one Ca, three equivalent Ir, and four P atoms. There are a spread of Ir–Ir bond distances ranging from 2.81–2.91 Å. There are a spread of Ir–P bond distances ranging from 2.32–2.58 Å. In the second Ir site, Ir is bonded in a 12-coordinate geometry to three equivalent Ca, five Ir, and four equivalent P atoms. Both Ir–Ir bond lengths are 2.77 Å. There are a spread of Ir–P bond distances ranging from 2.31–2.62 Å. There are two inequivalent P sites. In the first P site, P is bonded to six equivalent Ir atoms to form distorted PIr6 octahedra that share corners with six equivalent CaP6Ir12 cuboctahedra. In the second P site, P is bonded in a 9-coordinate geometry to two equivalent Ca and seven Ir atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CoIr by Materials Project

IrCo crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are two inequivalent Ir sites. In the first Ir site, Ir is bonded to six equivalent Ir and six Co atoms to form distorted IrCo6Ir6 cuboctahedra that share corners with twelve IrCo6Ir6 cuboctahedra, edges with twelve IrCo6Ir6 cuboctahedra, edges with twelve CoCo6Ir6 cuboctahedra, faces with six equivalent IrCo6Ir6 cuboctahedra, and faces with twelve CoCo6Ir6 cuboctahedra. All Ir–Ir bond lengths are 2.65 Å. All Ir–Co bond lengths are 2.58 Å. In the second Ir site, Ir is bonded to ten equivalent Ir and six Co atoms to form distorted IrCo6Ir10 cuboctahedra that share corners with ten CoCo6Ir6 cuboctahedra, corners with twelve IrCo6Ir6 cuboctahedra, edges with eight CoCo6Ir6 cuboctahedra, edges with sixteen IrCo6Ir6 cuboctahedra, faces with sixteen equivalent IrCo6Ir10 cuboctahedra, and faces with eighteen CoCo6Ir6 cuboctahedra. There are a spread of Ir–Ir bond distances ranging from 2.65–5.30 Å. All Ir–Co bond lengths are 2.58 Å. There are three inequivalent Co sites. In the first Co site, Co is bonded to six equivalent Ir and six equivalent Co atoms to form distorted CoCo6Ir6 cuboctahedra that share corners with twelve CoCo6Ir6 cuboctahedra, edges with twelve equivalent IrCo6Ir6 cuboctahedra, edges with twelve CoCo6Ir6 cuboctahedra, faces with six equivalent CoCo6Ir6 cuboctahedra, and faces with twelve equivalent IrCo6Ir6 cuboctahedra. All Co–Co bond lengths are 2.65 Å. In the second Co site, Co is bonded to six Ir and six equivalent Co atoms to form distorted CoCo6Ir6 cuboctahedra that share corners with five equivalent IrCo6Ir10 cuboctahedra, corners with twelve CoCo6Ir6 cuboctahedra, edges with ten IrCo6Ir6 cuboctahedra, edges with twelve CoCo6Ir6 cuboctahedra, faces with six equivalent CoCo6Ir6 cuboctahedra, and faces with fifteen IrCo6Ir6 cuboctahedra. All Co–Ir bond lengths are 2.58 Å. All Co–Co bond lengths are 2.65 Å. In the third Co site, Co is bonded to six Ir and six equivalent Co atoms to form distorted CoCo6Ir6 cuboctahedra that share corners with five equivalent IrCo6Ir10 cuboctahedra, corners with twelve CoCo6Ir6 cuboctahedra, edges with ten IrCo6Ir6 cuboctahedra, edges with twelve CoCo6Ir6 cuboctahedra, faces with six equivalent CoCo6Ir6 cuboctahedra, and faces with fifteen IrCo6Ir6 cuboctahedra. All Co–Co bond lengths are 2.65 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg2B2AsIr5 by Materials Project

Mg2Ir5B2As crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. there are two inequivalent Mg sites. In the first Mg site, Mg is bonded in a 11-coordinate geometry to two equivalent Mg, ten Ir, and three B atoms. Both Mg–Mg bond lengths are 2.99 Å. There are a spread of Mg–Ir bond distances ranging from 2.79–2.97 Å. There are one shorter (2.69 Å) and two longer (2.88 Å) Mg–B bond lengths. In the second Mg site, Mg is bonded in a 11-coordinate geometry to two equivalent Mg, ten Ir, and three B atoms. Both Mg–Mg bond lengths are 2.99 Å. There are a spread of Mg–Ir bond distances ranging from 2.79–2.97 Å. There are one shorter (2.69 Å) and two longer (2.88 Å) Mg–B bond lengths. There are two inequivalent Ir sites. In the first Ir site, Ir is bonded in a distorted body-centered cubic geometry to four equivalent Mg and four equivalent B atoms. All Ir–B bond lengths are 2.24 Å. In the second Ir site, Ir is bonded in a 2-coordinate geometry to four Mg, two equivalent B, and two equivalent As atoms. Both Ir–B bond lengths are 2.18 Å. Both Ir–As bond lengths are 2.63 Å. There are two inequivalent B sites. In the first B site, B is bonded in a 7-coordinate geometry to three Mg and six Ir atoms. All B–Ir bond lengths are 2.18 Å. In the second B site, B is bonded in a 7-coordinate geometry to three Mg and six Ir atoms. Both B–Ir bond lengths are 2.24 Å. As is bonded in a body-centered cubic geometry to eight equivalent Ir atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg2GaB2Ir5 by Materials Project

Mg2Ir5GaB2 crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. there are two inequivalent Mg sites. In the first Mg site, Mg is bonded in a 11-coordinate geometry to two equivalent Mg, ten Ir, and three B atoms. Both Mg–Mg bond lengths are 2.94 Å. There are a spread of Mg–Ir bond distances ranging from 2.77–2.96 Å. There are one shorter (2.66 Å) and two longer (2.90 Å) Mg–B bond lengths. In the second Mg site, Mg is bonded in a 11-coordinate geometry to two equivalent Mg, ten Ir, and three B atoms. Both Mg–Mg bond lengths are 2.94 Å. There are a spread of Mg–Ir bond distances ranging from 2.77–2.96 Å. There are one shorter (2.66 Å) and two longer (2.90 Å) Mg–B bond lengths. There are two inequivalent Ir sites. In the first Ir site, Ir is bonded in a distorted body-centered cubic geometry to four equivalent Mg and four equivalent B atoms. All Ir–B bond lengths are 2.25 Å. In the second Ir site, Ir is bonded in a 8-coordinate geometry to four Mg, two equivalent Ga, and two equivalent B atoms. Both Ir–Ga bond lengths are 2.61 Å. Both Ir–B bond lengths are 2.17 Å. Ga is bonded in a body-centered cubic geometry to eight equivalent Ir atoms. There are two inequivalent B sites. In the first B site, B is bonded in a 7-coordinate geometry to three Mg and six Ir atoms. All B–Ir bond lengths are 2.17 Å. In the second B site, B is bonded in a 7-coordinate geometry to three Mg and six Ir atoms. Both B–Ir bond lengths are 2.25 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Constructing Highly Porous Low Iridium Anode Catalysts Via Dealloying for Proton Exchange Membrane Water Electrolyzers

Iridium (Ir) is the most active and durable anode catalyst for the oxygen evolution reaction (OER) for proton exchange membrane water electrolyzers (PEMWEs). However, their large-scale applications are hindered by high costs and scarcity of Ir. Lowering Ir loadings below 1.0 mgcm -2 causes significantly reduced PEMWE performance and durability. Therefore, developing efficient low Ir-based catalysts is critical to widely commercializing PEMWEs. Herein, an approach is presented for designing porous Ir metal aerogel (MA) catalysts via chemically dealloying IrCu alloys. In this study, the unique hierarchical pore structures and multiple channels of the Ir MA catalyst significantly increase electrochemical surface area (ECSA) and enhance OER activity compared to conventional Ir black catalysts, providing an effective solution to design low-Ir catalysts with improved Ir utilization and enhanced stability. An optimized membrane electrode assembly (MEA) with an Ir loading of 0.5 mg Ir cm -2 generated 2.0 A cm -2 at 1.79 V, higher than the Ir black at a loading of 2.0 mg Ir cm -2 (1.63 A cm -2 ). The low-Ir MEA demonstrated an acceptable decay rate of ≈40 µV h -1 during durability tests at 0.5 (>1200 h) and 2.0 A cm -2 (400 h), outperforming the commercial Ir-based MEA (175 µV h -1 at 2.0 mg Ir cm -2 ).

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg2SiB2Ir5 by Materials Project

Mg2Ir5B2Si crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. there are two inequivalent Mg sites. In the first Mg site, Mg is bonded in a 11-coordinate geometry to two equivalent Mg, ten Ir, and three B atoms. Both Mg–Mg bond lengths are 2.91 Å. There are a spread of Mg–Ir bond distances ranging from 2.75–2.95 Å. There are one shorter (2.65 Å) and two longer (2.87 Å) Mg–B bond lengths. In the second Mg site, Mg is bonded in a 11-coordinate geometry to two equivalent Mg, ten Ir, and three B atoms. Both Mg–Mg bond lengths are 2.91 Å. There are a spread of Mg–Ir bond distances ranging from 2.75–2.95 Å. There are one shorter (2.65 Å) and two longer (2.87 Å) Mg–B bond lengths. There are two inequivalent Ir sites. In the first Ir site, Ir is bonded in a distorted body-centered cubic geometry to four equivalent Mg and four equivalent B atoms. All Ir–B bond lengths are 2.22 Å. In the second Ir site, Ir is bonded in a 8-coordinate geometry to four equivalent Mg, two equivalent B, and two equivalent Si atoms. Both Ir–B bond lengths are 2.19 Å. Both Ir–Si bond lengths are 2.54 Å. There are two inequivalent B sites. In the first B site, B is bonded in a 7-coordinate geometry to three Mg and six Ir atoms. In the second B site, B is bonded in a 7-coordinate geometry to three Mg and six Ir atoms. There are four shorter (2.19 Å) and two longer (2.22 Å) B–Ir bond lengths. Si is bonded in a body-centered cubic geometry to eight equivalent Ir atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ga9Ir2 by Materials Project

Ir2Ga9 crystallizes in the monoclinic Pc space group. The structure is three-dimensional. there are two inequivalent Ir sites. In the first Ir site, Ir is bonded in a 9-coordinate geometry to nine Ga atoms. There are a spread of Ir–Ga bond distances ranging from 2.49–2.71 Å. In the second Ir site, Ir is bonded in a 9-coordinate geometry to nine Ga atoms. There are a spread of Ir–Ga bond distances ranging from 2.49–2.66 Å. There are nine inequivalent Ga sites. In the first Ga site, Ga is bonded in a 2-coordinate geometry to two Ir atoms. In the second Ga site, Ga is bonded in a 2-coordinate geometry to two equivalent Ir atoms. In the third Ga site, Ga is bonded in a 2-coordinate geometry to two Ir atoms. In the fourth Ga site, Ga is bonded in a 2-coordinate geometry to two Ir atoms. In the fifth Ga site, Ga is bonded in a 2-coordinate geometry to two Ir atoms. In the sixth Ga site, Ga is bonded in a distorted bent 120 degrees geometry to two Ir atoms. In the seventh Ga site, Ga is bonded in a 2-coordinate geometry to two Ir atoms. In the eighth Ga site, Ga is bonded in a distorted bent 150 degrees geometry to two Ir atoms. In the ninth Ga site, Ga is bonded in a 2-coordinate geometry to two equivalent Ir atoms.

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