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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Mg(HO)2 by Materials Project

Mg(OH)2 crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one Mg(OH)2 sheet oriented in the (0, 0, 1) direction. Mg2+ is bonded to six equivalent O2- atoms to form edge-sharing MgO6 octahedra. All Mg–O bond lengths are 2.11 Å. H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.97 Å. O2- is bonded in a distorted single-bond geometry to three equivalent Mg2+ and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg(HO)2 by Materials Project

Mg(OH)2 crystallizes in the monoclinic C2 space group. The structure is two-dimensional and consists of one Mg(OH)2 sheet oriented in the (0, 0, 1) direction. Mg2+ is bonded to six equivalent O2- atoms to form edge-sharing MgO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.10–2.13 Å. H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.97 Å. O2- is bonded in a distorted single-bond geometry to three equivalent Mg2+ and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg(HO)2 by Materials Project

Mg(OH)2 crystallizes in the trigonal P3m1 space group. The structure is two-dimensional and consists of one Mg(OH)2 sheet oriented in the (0, 0, 1) direction. Mg2+ is bonded in a distorted q6 geometry to three equivalent H1+ and six O2- atoms. All Mg–H bond lengths are 1.97 Å. There are three shorter (2.11 Å) and three longer (2.23 Å) Mg–O bond lengths. There are two inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to three equivalent Mg2+ and one O2- atom. The H–O bond length is 0.99 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to three equivalent Mg2+ and one H1+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to three equivalent Mg2+ and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho13(Mg2Zn27)2 by Materials Project

Ho13(Mg2Zn27)2 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are two inequivalent Mg sites. In the first Mg site, Mg is bonded in a 6-coordinate geometry to three equivalent Ho and twelve Zn atoms. All Mg–Ho bond lengths are 3.11 Å. There are six shorter (2.82 Å) and six longer (3.15 Å) Mg–Zn bond lengths. In the second Mg site, Mg is bonded in a body-centered cubic geometry to eight Zn atoms. There are a spread of Mg–Zn bond distances ranging from 2.61–2.71 Å. There are four inequivalent Ho sites. In the first Ho site, Ho is bonded in a 3-coordinate geometry to sixteen Zn atoms. There are a spread of Ho–Zn bond distances ranging from 3.01–3.22 Å. In the second Ho site, Ho is bonded in a 12-coordinate geometry to one Mg and fourteen Zn atoms. There are a spread of Ho–Zn bond distances ranging from 3.00–3.29 Å. In the third Ho site, Ho is bonded in a 11-coordinate geometry to thirteen Zn atoms. There are a spread of Ho–Zn bond distances ranging from 2.96–3.24 Å. In the fourth Ho site, Ho is bonded in a 6-coordinate geometry to fourteen Zn atoms. There are a spread of Ho–Zn bond distances ranging from 2.88–3.49 Å. There are ten inequivalent Zn sites. In the first Zn site, Zn is bonded in a 10-coordinate geometry to four Ho and six Zn atoms. There are a spread of Zn–Zn bond distances ranging from 2.60–2.90 Å. In the second Zn site, Zn is bonded in a 1-coordinate geometry to two Mg, three Ho, and three Zn atoms. There are two shorter (2.62 Å) and one longer (2.63 Å) Zn–Zn bond lengths. In the third Zn site, Zn is bonded in a 9-coordinate geometry to three Ho and six Zn atoms. There are two shorter (2.55 Å) and two longer (2.88 Å) Zn–Zn bond lengths. In the fourth Zn site, Zn is bonded to two equivalent Ho and ten Zn atoms to form face-sharing ZnHo2Zn10 cuboctahedra. There are a spread of Zn–Zn bond distances ranging from 2.59–2.77 Å. In the fifth Zn site, Zn is bonded in a 12-coordinate geometry to four Ho and eight Zn atoms. There are a spread of Zn–Zn bond distances ranging from 2.54–2.97 Å. In the sixth Zn site, Zn is bonded in a 10-coordinate geometry to one Mg, four Ho, and five Zn atoms. There are two shorter (2.57 Å) and one longer (2.59 Å) Zn–Zn bond lengths. In the seventh Zn site, Zn is bonded in a 11-coordinate geometry to five Ho and six equivalent Zn atoms. In the eighth Zn site, Zn is bonded to three equivalent Ho and nine Zn atoms to form face-sharing ZnHo3Zn9 cuboctahedra. All Zn–Zn bond lengths are 2.65 Å. In the ninth Zn site, Zn is bonded in a 1-coordinate geometry to one Mg, three Ho, and five Zn atoms. In the tenth Zn site, Zn is bonded in a 1-coordinate geometry to one Mg, four Ho, and three Zn atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Effective point-charge analysis of crystal fields: Application to rare-earth pyrochlores and tripod kagome magnets 𝑅 ⁢3⁢ Mg⁢ 2 ⁢Sb⁢ 3⁢ O⁢ 14

An indispensable step to understand collective magnetic phenomena in rare-earth compounds is the determination of spatially anisotropic single-ion properties resulting from spin-orbit coupling and crystal field (CF). The CF Hamiltonian has a discrete energy spectrum—accessible to spectroscopic probes such as neutron scattering—controlled by a number of independent parameters reflecting the point symmetry of the magnetic sites. Determining these parameters in low-symmetry systems is often challenging. Here, we describe a general method to analyze CF excitation spectra using adjustable effective point-charges. We benchmark our method to existing neutron-scattering measurements on pyrochlore rare-earth oxides and obtain a universal point-charge model that describes a large family of related materials. We adapt this model to the newly discovered tripod kagome magnets (𝑅 3 ⁢Mg 2 ⁢Sb 3 ⁢O 14 , 𝑅 = Tb, Ho, Er, Yb) for which we report broadband inelastic neutron-scattering spectra. Analysis of these data using adjustable point-charges yields the CF wave functions for each compound. From this, we calculate thermomagnetic properties that accurately reflect our measurements on powder samples and predict the effective gyromagnetic tensor for pseudospin degrees of freedom—a crucial step to understand the exotic collective properties of these kagome magnets at low temperature. We present further applications of our method to other tripod kagome materials and triangular rare-earth compounds 𝑅⁢MgGaO 4 (𝑅 =Yb, Tm). Overall, this study establishes a widely applicable methodology to predict CF and single-ion properties of rare-earth compounds based on interpretable and adjustable models of effective point charges.

Crystal-field theory↗
DOE OSTI2020

Materials Data on Ho6Mg(GeS7)2 by Materials Project

MgHo6(GeS7)2 crystallizes in the trigonal P3 space group. The structure is three-dimensional. Mg2+ is bonded in an octahedral geometry to six S2- atoms. There are three shorter (2.56 Å) and three longer (2.59 Å) Mg–S bond lengths. There are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded in a 7-coordinate geometry to seven S2- atoms. There are a spread of Ho–S bond distances ranging from 2.72–3.03 Å. In the second Ho3+ site, Ho3+ is bonded in a 7-coordinate geometry to eight S2- atoms. There are a spread of Ho–S bond distances ranging from 2.71–3.38 Å. There are two inequivalent Ge4+ sites. In the first Ge4+ site, Ge4+ is bonded in a tetrahedral geometry to four S2- atoms. There are one shorter (2.21 Å) and three longer (2.24 Å) Ge–S bond lengths. In the second Ge4+ site, Ge4+ is bonded in a tetrahedral geometry to four S2- atoms. There are one shorter (2.22 Å) and three longer (2.24 Å) Ge–S bond lengths. There are six inequivalent S2- sites. In the first S2- site, S2- is bonded to three equivalent Ho3+ and one Ge4+ atom to form corner-sharing SHo3Ge tetrahedra. In the second S2- site, S2- is bonded to three equivalent Ho3+ and one Ge4+ atom to form corner-sharing SHo3Ge tetrahedra. In the third S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to three Ho3+ and one Ge4+ atom. In the fourth S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to three Ho3+ and one Ge4+ atom. In the fifth S2- site, S2- is bonded in a 4-coordinate geometry to one Mg2+ and four Ho3+ atoms. In the sixth S2- site, S2- is bonded to one Mg2+ and three Ho3+ atoms to form distorted SHo3Mg trigonal pyramids that share corners with three SHo3Ge tetrahedra and edges with two equivalent SHo3Mg trigonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho5Mg24 by Materials Project

Mg24Ho5 is alpha-derived structured and crystallizes in the cubic I-43m space group. The structure is three-dimensional. there are two inequivalent Mg sites. In the first Mg site, Mg is bonded in a 2-coordinate geometry to eleven Mg and two equivalent Ho atoms. There are a spread of Mg–Mg bond distances ranging from 2.99–3.38 Å. There are one shorter (3.22 Å) and one longer (3.71 Å) Mg–Ho bond lengths. In the second Mg site, Mg is bonded in a 12-coordinate geometry to eight Mg and four Ho atoms. There are one shorter (2.85 Å) and two longer (3.05 Å) Mg–Mg bond lengths. There are a spread of Mg–Ho bond distances ranging from 3.44–3.62 Å. There are two inequivalent Ho sites. In the first Ho site, Ho is bonded in a 12-coordinate geometry to twelve equivalent Mg and four equivalent Ho atoms. All Ho–Ho bond lengths are 3.60 Å. In the second Ho site, Ho is bonded in a 3-coordinate geometry to fifteen Mg and one Ho atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho8Mg12Zn61 by Materials Project

Mg12Ho8Zn61 is Bergman Structure: Mg32(Al,Zn)49 Bergman-like structured and crystallizes in the cubic Im-3 space group. The structure is three-dimensional. Mg is bonded in a 10-coordinate geometry to one Mg, two equivalent Ho, and twelve Zn atoms. The Mg–Mg bond length is 3.29 Å. Both Mg–Ho bond lengths are 3.37 Å. There are a spread of Mg–Zn bond distances ranging from 2.92–3.29 Å. Ho is bonded in a 12-coordinate geometry to three equivalent Mg, one Ho, and twelve Zn atoms. The Ho–Ho bond length is 3.09 Å. There are a spread of Ho–Zn bond distances ranging from 2.94–3.19 Å. There are six inequivalent Zn sites. In the first Zn site, Zn is bonded in a 12-coordinate geometry to three equivalent Mg, two equivalent Ho, and seven Zn atoms. There are a spread of Zn–Zn bond distances ranging from 2.50–2.80 Å. In the second Zn site, Zn is bonded in a 11-coordinate geometry to two equivalent Mg, two equivalent Ho, and seven Zn atoms. There are a spread of Zn–Zn bond distances ranging from 2.59–3.02 Å. In the third Zn site, Zn is bonded to two equivalent Mg, two equivalent Ho, and eight Zn atoms to form a mixture of distorted face, edge, and corner-sharing ZnHo2Mg2Zn8 cuboctahedra. There are a spread of Zn–Zn bond distances ranging from 2.62–3.01 Å. In the fourth Zn site, Zn is bonded in a cuboctahedral geometry to twelve equivalent Zn atoms. In the fifth Zn site, Zn is bonded to four equivalent Mg and eight Zn atoms to form a mixture of distorted face, edge, and corner-sharing ZnMg4Zn8 cuboctahedra. There are one shorter (2.54 Å) and one longer (2.71 Å) Zn–Zn bond lengths. In the sixth Zn site, Zn is bonded in a 2-coordinate geometry to two equivalent Mg and eleven Zn atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MgAl2As2(HO)18 by Materials Project

MgAl2As2(H7O8)2(H2O)2 crystallizes in the triclinic P-1 space group. The structure is three-dimensional and consists of two water molecules and one MgAl2As2(H7O8)2 framework. In the MgAl2As2(H7O8)2 framework, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with two equivalent AsO4 tetrahedra. There are a spread of Mg–O bond distances ranging from 2.07–2.13 Å. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent AlO6 octahedra and corners with two equivalent AsO4 tetrahedra. The corner-sharing octahedral tilt angles are 42°. There are a spread of Al–O bond distances ranging from 1.88–2.00 Å. In the second Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent AlO6 octahedra and corners with four equivalent AsO4 tetrahedra. The corner-sharing octahedral tilt angles are 42°. There are a spread of Al–O bond distances ranging from 1.89–1.95 Å. As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share a cornercorner with one MgO6 octahedra and corners with three AlO6 octahedra. The corner-sharing octahedra tilt angles range from 45–56°. There is three shorter (1.72 Å) and one longer (1.73 Å) As–O bond length. There are seven inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a distorted single-bond geometry to two O2- atoms. There is one shorter (1.02 Å) and one longer (1.61 Å) H–O bond length. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the third H1+ site, H1+ is bonded in a distorted single-bond geometry to one O2- atom. The H–O bond length is 1.01 Å. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to two O2- atoms. There is one shorter (1.00 Å) and one longer (1.73 Å) H–O bond length. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted water-like geometry to one Al3+ and two H1+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to one Mg2+ and two H1+ atoms. In the third O2- site, O2- is bonded in a distorted water-like geometry to one Mg2+ and two H1+ atoms. In the fourth O2- site, O2- is bonded in a distorted single-bond geometry to two Al3+ and one H1+ atom. In the fifth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one Al3+, one As5+, and one H1+ atom. In the sixth O2- site, O2- is bonded in a bent 120 degrees geometry to one Al3+ and one As5+ atom. In the seventh O2- site, O2- is bonded in a trigonal planar geometry to one Al3+, one As5+, and one H1+ atom. In the eighth O2- site, O2- is bonded in a 2-coordinate geometry to one Mg2+ and one As5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg3P2(HO)16 by Materials Project

Mg3P2(HO)16 crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of two Mg3P2(HO)16 sheets oriented in the (0, 1, 0) direction. there are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with two equivalent PO4 tetrahedra. There are two shorter (2.06 Å) and four longer (2.14 Å) Mg–O bond lengths. In the second Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with four equivalent PO4 tetrahedra and an edgeedge with one MgO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.08–2.16 Å. P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with five MgO6 octahedra. The corner-sharing octahedra tilt angles range from 46–56°. There are a spread of P–O bond distances ranging from 1.55–1.58 Å. There are four inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the third H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.01 Å. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to two O2- atoms. There is one shorter (1.00 Å) and one longer (1.73 Å) H–O bond length. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one Mg2+ and two H1+ atoms. In the second O2- site, O2- is bonded in a distorted water-like geometry to one Mg2+ and two H1+ atoms. In the third O2- site, O2- is bonded in a 2-coordinate geometry to one Mg2+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Mg2+ and one P5+ atom. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to one Mg2+, one P5+, and two equivalent H1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg4Al2H12CO18 by Materials Project

(Mg2Al(HO)6)4(CO3)2(O2)3 crystallizes in the trigonal P31m space group. The structure is two-dimensional and consists of one carbonic acid molecule; three water molecules; and two Mg2Al(HO)6 sheets oriented in the (0, 0, 1) direction. In each Mg2Al(HO)6 sheet, Mg is bonded to six O atoms to form MgO6 octahedra that share edges with three equivalent MgO6 octahedra and edges with three equivalent AlO6 octahedra. There are three shorter (2.09 Å) and three longer (2.10 Å) Mg–O bond lengths. Al is bonded to six O atoms to form AlO6 octahedra that share edges with six equivalent MgO6 octahedra. All Al–O bond lengths are 1.93 Å. There are two inequivalent H sites. In the first H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.99 Å. In the second H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.98 Å. There are two inequivalent O sites. In the first O site, O is bonded in a 1-coordinate geometry to two equivalent Mg, one Al, and one H atom. In the second O site, O is bonded in a 1-coordinate geometry to two equivalent Mg, one Al, and one H atom.

36 MATERIALS SCIENCE↗
NASA NTRS2022

Trace Element Partitioning Between Olivine and Melt in Lunar Basalts

Mineral/melt partition coefficients have been widely used to provide insights into magmatic processes. Olivine is one of the most abundant and important minerals in the lunar mantle and mare basalts. Yet, no systematic olivine/melt partitioning data are available for lunar conditions. We report trace element partition data between host mineral olivine and its melt inclusions in lunar basalts. Equilibrium is evaluated using the Fe-Mg exchange coefficient, leading to the choice of melt inclusion-host olivine pairs in lunar basalts 12040, 12009, 15016, 15647, and 74235. Partition coefficients of 21 elements (Li, Mg, Al, Ca, Ti, V, Cr, Mn, Fe, Co, Y, Zr, Nb, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) were measured. Except for Li, V, and Cr, these elements show no significant difference in olivine-melt partitioning compared to the data for terrestrial samples. The partition coefficient of Li between olivine and melt in some lunar basalts with low Mg# (Mg# < 0.75 in olivine, or < ~0.5 in melt) is higher than published data for terrestrial * Corresponding author. Email address: youxue@umich.edu 2 samples, which is attributed to the dependence of DLi on Mg# and the lack of literature DLi data with low Mg#. The partition coefficient of V in lunar basalts is measured to be 0.17 to 0.74, significantly higher than that in terrestrial basalts (0.003 to 0.21), which can be explained by the lower oxygen fugacity in lunar basalts. The significantly higher DV can explain why V is less enriched in evolved lunar basalts than terrestrial basalts. The partition coefficient of Cr between olivine and basalt melt in the Moon is 0.11 to 0.62, which is lower than those in terrestrial settings by a factor of approximately 2. This is surprising because previous authors showed that Cr partition coefficient is independent of fO2. A quasi-thermodynamically based model is developed to correlate Cr partition coefficient to olivine and melt composition and fO2. The lower Cr partition coefficient between olivine and basalt in the Moon can lead to more Cr enrichment in the lunar magma ocean, as well as more Cr enrichment in mantle-derived basalts in the Moon. Hence, even though Cr is typically a compatible element in terrestrial basalts, it is moderately incompatible in primitive lunar basalts, with a similar degree of incompatibility as V based on partition coefficients in this work, as also evidenced by the relatively constant V/Cr ratio of 0.039 ± 0.011 in lunar basalts. The confirmation of constant V/Cr ratio is important for constraining concentrations of Cr (slightly volatile and siderophile) and V (slightly siderophile) in the bulk silicate Moon.

partition coefficients↗
DOE OSTI2020

Materials Data on CaMgB6(HO)22 by Materials Project

CaMgB6(H9O10)2(H2O)2 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional and consists of eight water molecules and one CaMgB6(H9O10)2 framework. In the CaMgB6(H9O10)2 framework, Ca2+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ca–O bond distances ranging from 2.41–2.54 Å. Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with four BO4 tetrahedra. There are a spread of Mg–O bond distances ranging from 2.11–2.13 Å. There are three inequivalent B3+ sites. In the first B3+ site, B3+ is bonded to four O2- atoms to form BO4 tetrahedra that share a cornercorner with one MgO6 octahedra and a cornercorner with one BO4 tetrahedra. The corner-sharing octahedral tilt angles are 58°. There are a spread of B–O bond distances ranging from 1.45–1.50 Å. In the second B3+ site, B3+ is bonded to four O2- atoms to form BO4 tetrahedra that share a cornercorner with one MgO6 octahedra and a cornercorner with one BO4 tetrahedra. The corner-sharing octahedral tilt angles are 58°. There are a spread of B–O bond distances ranging from 1.45–1.52 Å. In the third B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There is two shorter (1.37 Å) and one longer (1.39 Å) B–O bond length. There are nine inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.97 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the third H1+ site, H1+ is bonded in a distorted single-bond geometry to two O2- atoms. There is one shorter (1.00 Å) and one longer (1.62 Å) H–O bond length. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the eighth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the ninth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. There are ten inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ca2+, one B3+, and one H1+ atom. In the second O2- site, O2- is bonded in a bent 120 degrees geometry to two B3+ atoms. In the third O2- site, O2- is bonded in a bent 120 degrees geometry to two B3+ atoms. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ca2+, one B3+, and one H1+ atom. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to one B3+ and two H1+ atoms. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one B3+, and one H1+ atom. In the seventh O2- site, O2- is bonded in a distorted water-like geometry to one Mg2+ and two H1+ atoms. In the eighth O2- site, O2- is bonded in a distorted water-like geometry to one Ca2+ and two H1+ atoms. In the ninth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ca2+ and two B3+ atoms. In the tenth O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one B3+, and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Mineralogy of the deep lower mantle in the presence of H 2 O

Understanding the mineralogy of the Earth's interior is a prerequisite for unravelling the evolution and dynamics of our planet. Here, we conducted high pressure-temperature experiments mimicking the conditions of the deep lower mantle (DLM, 1800–2890 km in depth) and observed surprising mineralogical transformations in the presence of water. Ferropericlase, (Mg, Fe)O, which is the most abundant oxide mineral in Earth, reacts with H 2 O to form a previously unknown (Mg, Fe)O 2 H x (x ≤ 1) phase. The (Mg, Fe)O 2 H x has a pyrite structure and it coexists with the dominant silicate phases, bridgmanite and post-perovskite. Depending on Mg content and geotherm temperatures, the transformation may occur at 1800 km for (Mg 0.6 Fe 0.4 )O or beyond 2300 km for (Mg 0.7 Fe 0.3 )O. The (Mg, Fe)O 2 H x is an oxygen excess phase that stores an excessive amount of oxygen beyond the charge balance of maximum cation valences (Mg 2+ , Fe 3+ and H + ). This important phase has a number of far-reaching implications including extreme redox inhomogeneity, deep-oxygen reservoirs in the DLM and an internal source for modulating oxygen in the atmosphere.

58 GEOSCIENCES↗
DOE OSTI2020

Materials Data on MgP2(HO)18 by Materials Project

MgP2(H2O3)4(H2O)4H2O2 crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of four water molecules, two water molecules, and one MgP2(H2O3)4 cluster. In the MgP2(H2O3)4 cluster, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with two equivalent PO4 tetrahedra. There are four shorter (2.08 Å) and two longer (2.15 Å) Mg–O bond lengths. P is bonded to four O atoms to form PO4 tetrahedra that share a cornercorner with one MgO6 octahedra. The corner-sharing octahedral tilt angles are 47°. There are a spread of P–O bond distances ranging from 1.54–1.56 Å. There are four inequivalent H sites. In the first H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.98 Å. In the second H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.99 Å. In the third H site, H is bonded in a distorted single-bond geometry to one O atom. The H–O bond length is 1.00 Å. In the fourth H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.99 Å. There are six inequivalent O sites. In the first O site, O is bonded in a distorted bent 120 degrees geometry to one Mg and one P atom. In the second O site, O is bonded in a single-bond geometry to one P atom. In the third O site, O is bonded in a 2-coordinate geometry to one Mg and two H atoms. In the fourth O site, O is bonded in a distorted trigonal planar geometry to one Mg and two H atoms. In the fifth O site, O is bonded in a single-bond geometry to one P atom. In the sixth O site, O is bonded in a single-bond geometry to one P atom.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Prediction of ambient pressure superconductivity in cubic ternary hydrides with MH 6 octahedra

Exploring high-temperature superconducting (high-T c ) material at ambient pressure holds immense significance for physics, chemistry, and materials science. In this study, we perform a high-throughput screening of strong electron-phonon interactions in X 2 MH 6 compounds (X = Li, Na, Mg, Al, K, Ca, Ga, Rb, Sr, and In; M are 3d, 4d, and 5d transition metals). These compounds have a cubic structure featuring an MH 6 octahedron motif. Our screening calculations suggest that 26 compounds exhibit dynamic stability and strong electron-phonon coupling. Among them, Mg 2 RhH 6 , Mg 2 IrH 6 , Al 2 MnH 6 , and Li 2 CuH 6 show promising energetic stability and T c of more than 50 K at ambient pressure. This study underscores promising high-T c compounds at ambient pressure with distinctive MH 6 motifs.

36 MATERIALS SCIENCE↗