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DOE OSTI2020

Materials Data on TiFeGe2 by Materials Project

TiFeGe2 crystallizes in the orthorhombic Pbam space group. The structure is three-dimensional. there are two inequivalent Ti sites. In the first Ti site, Ti is bonded in a 8-coordinate geometry to eight Ge atoms. There are a spread of Ti–Ge bond distances ranging from 2.60–2.88 Å. In the second Ti site, Ti is bonded in a 7-coordinate geometry to seven Ge atoms. There are a spread of Ti–Ge bond distances ranging from 2.63–2.83 Å. There are two inequivalent Fe sites. In the first Fe site, Fe is bonded in a 12-coordinate geometry to six Ge atoms. There are a spread of Fe–Ge bond distances ranging from 2.35–2.53 Å. In the second Fe site, Fe is bonded to six Ge atoms to form distorted edge-sharing FeGe6 cuboctahedra. There are a spread of Fe–Ge bond distances ranging from 2.41–2.50 Å. There are five inequivalent Ge sites. In the first Ge site, Ge is bonded in a 9-coordinate geometry to six Ti, two equivalent Fe, and one Ge atom. The Ge–Ge bond length is 2.48 Å. In the second Ge site, Ge is bonded in a 2-coordinate geometry to four equivalent Ti, two equivalent Fe, and one Ge atom. The Ge–Ge bond length is 2.52 Å. In the third Ge site, Ge is bonded in a 9-coordinate geometry to five Ti and four Fe atoms. In the fourth Ge site, Ge is bonded in a 6-coordinate geometry to two equivalent Ti and four Fe atoms. In the fifth Ge site, Ge is bonded in a 7-coordinate geometry to three Ti, three Fe, and one Ge atom. The Ge–Ge bond length is 2.52 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Li2Ti3FeO8 by Materials Project

Li2Ti3FeO8 is Spinel-derived structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are eight inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded to six O2- atoms to form LiO6 octahedra that share corners with three LiO4 tetrahedra, corners with three FeO4 tetrahedra, and edges with six TiO6 octahedra. There are a spread of Li–O bond distances ranging from 2.15–2.17 Å. In the second Li1+ site, Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with three LiO6 octahedra and corners with nine TiO6 octahedra. The corner-sharing octahedra tilt angles range from 54–65°. There are a spread of Li–O bond distances ranging from 2.00–2.04 Å. In the third Li1+ site, Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with three LiO6 octahedra and corners with nine TiO6 octahedra. The corner-sharing octahedra tilt angles range from 55–65°. There are one shorter (2.01 Å) and three longer (2.03 Å) Li–O bond lengths. In the fourth Li1+ site, Li1+ is bonded to six O2- atoms to form LiO6 octahedra that share corners with three LiO4 tetrahedra, corners with three FeO4 tetrahedra, and edges with six TiO6 octahedra. There are a spread of Li–O bond distances ranging from 2.14–2.18 Å. In the fifth Li1+ site, Li1+ is bonded to six O2- atoms to form LiO6 octahedra that share corners with three LiO4 tetrahedra, corners with three FeO4 tetrahedra, and edges with six TiO6 octahedra. There are a spread of Li–O bond distances ranging from 2.14–2.17 Å. In the sixth Li1+ site, Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with three LiO6 octahedra and corners with nine TiO6 octahedra. The corner-sharing octahedra tilt angles range from 54–65°. There are a spread of Li–O bond distances ranging from 2.00–2.04 Å. In the seventh Li1+ site, Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with three LiO6 octahedra and corners with nine TiO6 octahedra. The corner-sharing octahedra tilt angles range from 54–65°. There are a spread of Li–O bond distances ranging from 2.00–2.04 Å. In the eighth Li1+ site, Li1+ is bonded to six O2- atoms to form LiO6 octahedra that share corners with three LiO4 tetrahedra, corners with three FeO4 tetrahedra, and edges with six TiO6 octahedra. There are a spread of Li–O bond distances ranging from 2.14–2.18 Å. There are twelve inequivalent Ti4+ sites. In the first Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with three LiO4 tetrahedra, corners with three FeO4 tetrahedra, edges with two LiO6 octahedra, and edges with four TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.88–2.09 Å. In the second Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with three LiO4 tetrahedra, corners with three FeO4 tetrahedra, edges with two LiO6 octahedra, and edges with four TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.88–2.08 Å. In the third Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with three LiO4 tetrahedra, corners with three FeO4 tetrahedra, edges with two LiO6 octahedra, and edges with four TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.89–2.09 Å. In the fourth Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with three LiO4 tetrahedra, corners with three FeO4 tetrahedra, edges with two LiO6 octahedra, and edges with four TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.89–2.08 Å. In the fifth Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with three LiO4 tetrahedra, corners with three FeO4 tetrahedra, edges with two LiO6 octahedra, and edges with four TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.89–2.08 Å. In the sixth Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with three LiO4 tetrahedra, corners with three FeO4 tetrahedra, edges with two LiO6 octahedra, and edges with four TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.88–2.08 Å. In the seventh Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with three LiO4 tetrahedra, corners with three FeO4 tetrahedra, edges with two LiO6 octahedra, and edges with four TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.88–2.09 Å. In the eighth Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with three LiO4 tetrahedra, corners with three FeO4 tetrahedra, edges with two LiO6 octahedra, and edges with four TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.88–2.08 Å. In the ninth Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with three LiO4 tetrahedra, corners with three FeO4 tetrahedra, edges with two LiO6 octahedra, and edges with four TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.88–2.09 Å. In the tenth Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with three LiO4 tetrahedra, corners with three FeO4 tetrahedra, edges with two LiO6 octahedra, and edges with four TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.89–2.09 Å. In the eleventh Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with three LiO4 tetrahedra, corners with three FeO4 tetrahedra, edges with two LiO6 octahedra, and edges with four TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.88–2.09 Å. In the twelfth Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with three LiO4 tetrahedra, corners with three FeO4 tetrahedra, edges with two LiO6 octahedra, and edges with four TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.88–2.09 Å. There are four inequivalent Fe2+ sites. In the first Fe2+ site, Fe2+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with three LiO6 octahedra and corners with nine TiO6 octahedra. The corner-sharing octahedra tilt angles range from 56–65°. There are three shorter (2.02 Å) and one longer (2.03 Å) Fe–O bond lengths. In the second Fe2+ site, Fe2+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with three LiO6 octahedra and corners with nine TiO6 octahedra. The corner-sharing octahedra tilt angles range from 56–65°. There are a spread of Fe–O bond distances ranging from 2.01–2.03 Å. In the third Fe2+ site, Fe2+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with three LiO6 octahedra and corners with nine TiO6 octahedra. The corner-sharing octahedra tilt angles range from 56–65°. There are three shorter (2.02 Å) and one longer (2.03 Å) Fe–O bond lengths. In the fourth Fe2+ site, Fe2+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with three LiO6 octahedra and corners with nine TiO6 octahedra. The corner-sharing octahedra tilt angles range from 56–65°. There are a spread of Fe–O bond distances ranging from 2.01–2.03 Å. There are thirty-two inequivalent O2- sites. In the first O2- site, O2- is bonded to two Li1+ and two Ti4+ atoms to form distorted OLi2Ti2 trigonal pyramids that share corners with twelve OLiTi2Fe trigonal pyramids and edges with three OLi2Ti2 trigonal pyramids. In the second O2- site, O2- is bonded to two Li1+ and two Ti4+ atoms to form distorted OLi2Ti2 trigonal pyramids that share corners with twelve OLiTi2Fe trigonal pyramids and edges with three OLi2Ti2 trigonal pyramids. In the third O2- site, O2- is bonded to one Li1+ and three Ti4+ atoms to form distorted OLiTi3 trigonal pyramids that share corners with twelve OLiTi2Fe trigonal pyramids and edges with three OLi2Ti2 trigonal pyramids. In the fourth O2- site, O2- is bonded to two Li1+ and two Ti4+ atoms to form distorted OLi2Ti2 trigonal pyramids that share corners with twelve OLiTi2Fe trigonal pyramids and edges with three OLiTi3 trigonal pyramids. In the fifth O2- site, O2- is bonded to one Li1+, two Ti4+, and one Fe2+ atom to form distorted OLiTi2Fe trigonal pyramids that share corners with twelve OLi2Ti2 trigonal pyramids and edges with three OLiTi2Fe trigonal pyramids. In the sixth O2- site, O2- is bonded to three Ti4+ and one Fe2+ atom to form distorted OTi3Fe trigonal pyramids that share corners with twelve OLi2Ti2 trigonal pyramids and edges with three OLiTi2Fe trigonal pyramids. In the seventh O2- site, O2- is bonded to one Li1+, two Ti4+, and one Fe2+ atom to form distorted OLiTi2Fe trigonal pyramids that share corners with twelve OLi2Ti2 trigonal pyramids and edges with three OTi3Fe trigonal pyramids. In the eighth O2- site, O2- is bonded to one Li1+, two Ti4+, and one Fe2+ atom to form distorted OLiTi2Fe trigonal pyramids that share corners with twelve OLi2Ti2 trigonal pyramids and edges with three OTi3Fe trigonal pyramids. In the ninth O2- site, O2- is bonded to one Li1+, two Ti4+, and one Fe2+ atom to form a mixture of distorted corner and edge-sharing OLiTi2Fe trigonal pyramids. In the tenth O2- site, O2- is bonded to one Li1+, two Ti4+, and one Fe2+ atom to form distorted OLiTi2Fe trigonal pyramids that share corners with twelve OTi3Fe trigonal pyramids and edges with three OLiTi2Fe trigonal pyramids. In the eleventh O2- site, O2- is bonded to three Ti4+ and one Fe2+ atom to form a mixture of distorted corner and edge-sharing OTi3Fe trigonal pyramids. In the twelfth O2- site, O2- is bonded to one Li1+, two Ti4+, and one Fe2+ atom to form distorted OLiTi2Fe trigonal pyramids that share corners with twelve OLiTi2Fe trigonal pyramids and edges with three OTi3Fe trigonal pyramids. In the thirteenth O2- site, O2- is bonded to two Li1+ and two Ti4+ atoms to form distorted OLi2Ti2 trigonal pyramids that share corners with twelve OLiTi2Fe trigonal pyramids and edges with three OLi2Ti2 trigonal pyramids. In the fourteenth O2- site, O2- is bonded to one Li1+ and three Ti4+ atoms to form distorted OLiTi3 trigonal pyramids that share corners with twelve OLiTi2Fe trigonal pyramids and edges with three OLi2Ti2 trigonal pyramids. In the fifteenth O2- site, O2- is bonded to two Li1+ and two Ti4+ atoms to form distorted OLi2Ti2 trigonal pyramids that share corners with twelve OLiTi2Fe trigonal pyramids and edges with three OLiTi3 trigonal pyramids. In the sixteenth O2- site, O2- is bonded to two Li1+ and two Ti4+ atoms to form distorted OLi2Ti2 trigonal pyramids that share corners with twelve OLiTi2Fe trigonal pyramids and edges with three OLiTi3 trigonal pyramids. In the seventeenth O2- site, O2- is bonded to two Li1+ and two Ti4+ atoms to form distorted OLi2Ti2 trigonal pyramids that share corners with twelve OLiTi2Fe trigonal pyramids and edges with three OLi2Ti2 trigonal pyramids. In the eighteenth O2- site, O2- is bonded to two Li1+ and two Ti4+ atoms to form distorted OLi2Ti2 trigonal pyramids that share corners with twelve OTi3Fe trigonal pyramids and edges with three OLi2Ti2 trigonal pyramids. In the nineteenth O2- site, O2- is bonded to one Li1+ and three Ti4+ atoms to form distorted OLiTi3 trigonal pyramids that share corners with twelve OTi3Fe trigonal pyramids and edges with three OLi2Ti2 trigonal pyramids. In the twentieth O2- site, O2- is bonded to two Li1+ and two Ti4+ atoms to form distorted OLi2Ti2 trigonal pyramids that share corners with twelve OLiTi2Fe trigonal pyramids and edges with three OLiTi3 trigonal pyramids. In the twenty-first O2- site, O2- is bonded to one Li1+, two Ti4+, and one Fe2+ atom to form a mixture of distorted corner and edge-sharing OLiTi2Fe trigonal pyramids. In the twenty-second O2- site, O2- is bonded to three Ti4+ and one Fe2+ atom to form a mixture of distorted corner and edge-sharing OTi3Fe trigonal pyramids. In the twenty-third O2- site, O2- is bonded to one L

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na4Ti4Si3O22 by Materials Project

Na4Ti4Si3O16(O2)3 crystallizes in the trigonal R3m space group. The structure is three-dimensional and consists of three hexaoxane molecules and one Na4Ti4Si3O16 framework. In the Na4Ti4Si3O16 framework, there are two inequivalent Na sites. In the first Na site, Na is bonded to four O atoms to form distorted NaO4 trigonal pyramids that share corners with six equivalent TiO6 octahedra and corners with three equivalent SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 36–62°. There are one shorter (2.21 Å) and three longer (2.90 Å) Na–O bond lengths. In the second Na site, Na is bonded in a 4-coordinate geometry to four O atoms. There are two shorter (2.38 Å) and two longer (2.68 Å) Na–O bond lengths. There are two inequivalent Ti sites. In the first Ti site, Ti is bonded to six O atoms to form TiO6 octahedra that share corners with three equivalent SiO4 tetrahedra and edges with three equivalent TiO6 octahedra. There is three shorter (1.94 Å) and three longer (1.96 Å) Ti–O bond length. In the second Ti site, Ti is bonded to six O atoms to form TiO6 octahedra that share corners with three equivalent SiO4 tetrahedra, corners with two equivalent NaO4 trigonal pyramids, and edges with three TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.92–2.07 Å. Si is bonded to four O atoms to form SiO4 tetrahedra that share corners with four TiO6 octahedra and a cornercorner with one NaO4 trigonal pyramid. The corner-sharing octahedra tilt angles range from 52–54°. There are a spread of Si–O bond distances ranging from 1.64–1.66 Å. There are five inequivalent O sites. In the first O site, O is bonded in a tetrahedral geometry to one Na and three equivalent Ti atoms. In the second O site, O is bonded in a distorted trigonal non-coplanar geometry to three Ti atoms. In the third O site, O is bonded in a 4-coordinate geometry to two equivalent Na, one Ti, and one Si atom. In the fourth O site, O is bonded in a distorted bent 120 degrees geometry to one Na, one Ti, and one Si atom. In the fifth O site, O is bonded in a 2-coordinate geometry to one Na, one Ti, and one Si atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ti4Al2CN by Materials Project

Ti4Al2CN is H-Phase-derived structured and crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. there are two inequivalent Ti sites. In the first Ti site, Ti is bonded in a 3-coordinate geometry to three equivalent Al and three equivalent N atoms. All Ti–Al bond lengths are 2.86 Å. All Ti–N bond lengths are 2.09 Å. In the second Ti site, Ti is bonded in a 3-coordinate geometry to three equivalent Al and three equivalent C atoms. All Ti–Al bond lengths are 2.87 Å. All Ti–C bond lengths are 2.10 Å. Al is bonded to six Ti and six equivalent Al atoms to form distorted AlTi6Al6 cuboctahedra that share corners with six equivalent AlTi6Al6 cuboctahedra, corners with three equivalent CTi6 octahedra, corners with three equivalent NTi6 octahedra, edges with six equivalent AlTi6Al6 cuboctahedra, edges with three equivalent CTi6 octahedra, edges with three equivalent NTi6 octahedra, and faces with six equivalent AlTi6Al6 cuboctahedra. The corner-sharing octahedral tilt angles are 19°. All Al–Al bond lengths are 3.04 Å. C is bonded to six equivalent Ti atoms to form CTi6 octahedra that share corners with six equivalent AlTi6Al6 cuboctahedra, edges with six equivalent AlTi6Al6 cuboctahedra, and edges with six equivalent CTi6 octahedra. N is bonded to six equivalent Ti atoms to form NTi6 octahedra that share corners with six equivalent AlTi6Al6 cuboctahedra, edges with six equivalent AlTi6Al6 cuboctahedra, and edges with six equivalent NTi6 octahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TaTi3 by Materials Project

Ti3Ta crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent Ti sites. In the first Ti site, Ti is bonded to eight Ti and four equivalent Ta atoms to form TiTa4Ti8 cuboctahedra that share corners with twelve equivalent TiTa4Ti8 cuboctahedra, edges with eight equivalent TaTi12 cuboctahedra, edges with sixteen TiTa4Ti8 cuboctahedra, faces with four equivalent TaTi12 cuboctahedra, and faces with fourteen TiTa4Ti8 cuboctahedra. There are four shorter (2.83 Å) and four longer (2.97 Å) Ti–Ti bond lengths. All Ti–Ta bond lengths are 2.97 Å. In the second Ti site, Ti is bonded to eight equivalent Ti and four equivalent Ta atoms to form TiTa4Ti8 cuboctahedra that share corners with four equivalent TiTa4Ti8 cuboctahedra, corners with eight equivalent TaTi12 cuboctahedra, edges with twenty-four TiTa4Ti8 cuboctahedra, faces with six equivalent TaTi12 cuboctahedra, and faces with twelve TiTa4Ti8 cuboctahedra. All Ti–Ta bond lengths are 2.83 Å. Ta is bonded to twelve Ti atoms to form TaTi12 cuboctahedra that share corners with four equivalent TaTi12 cuboctahedra, corners with eight equivalent TiTa4Ti8 cuboctahedra, edges with eight equivalent TaTi12 cuboctahedra, edges with sixteen equivalent TiTa4Ti8 cuboctahedra, faces with four equivalent TaTi12 cuboctahedra, and faces with fourteen TiTa4Ti8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Titanium isotope systematics of refractory inclusions: Echoes of molecular cloud heterogeneity

Calcium-aluminum-rich inclusions (CAIs) are highly refractory objects found in different chondrite groups and represent some of the oldest known solids of the Solar System. As such, CAIs provide key information regarding the conditions prevailing in the solar protoplanetary disk as well as subsequent mixing and transport processes. Many studies have investigated CAIs for their isotopic compositions and reported nucleosynthetic isotope anomalies in numerous elements, which are typically explained by the variable incorporation of isotopically highly anomalous presolar phases. However, with the exception of 54 Cr-enriched nanospinels, the exact presolar phases responsible for the isotopic heterogeneities are yet to be identified. To address this issue, we here present in-situ Ti isotopic analyses obtained on a diverse set of CAIs from various CV3 chondrites. In this work, the in-situ measurements were performed by targeting individual mineral phases of 15 CAIs with laser-ablation mass spectrometry and indicate significant inter- and intra-CAI isotopic heterogeneity in the neutron-rich isotope 50 Ti. This is particularly pronounced for primitive fine-grained CAIs, whereas coarse-grained CAIs, which have been subject to melting, exhibit smaller degrees of Ti isotopic heterogeneity. To further investigate this Ti isotopic heterogeneity, we additionally obtained Ti isotopic compositions of sequential acid leachates from two fine-grained and two coarse-grained CAIs derived from CV3 chondrites. In contrast to potential expectations from the first part of the study, we do not observe any significant intra-CAI Ti isotopic heterogeneity between the different leaching steps. The lack of intra-CAI Ti isotopic heterogeneity in the acid leachate samples of this study likely reflects that the leaching procedure is unable to efficiently separate the carriers of isotopically anomalous Ti in CAIs. By comparing the bulk CAI Ti isotope compositions with Ti isotope data for hibonite-rich objects from the literature, we find that the range of Ti isotope compositions recorded by CAIs from various chondrite groups can be accounted for by the averaging of hibonite grains. In turn, the variable Ti isotope compositions of hibonite grains can be explained by the averaging of isotopically diverse presolar grains present in the Sun’s parental molecular cloud. This effect of averaging is statistically supported by the central limit theorem, and the concept has the potential to be useful for other isotopic systems.

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

Transition state stabilization depends on solvent identity, pore size, and hydrophilicity for epoxidations in zeolites

Ti-silicates activate H 2 O 2 to form Ti-hydroperoxo and Ti-peroxo intermediates that can react with alkenes to form epoxide products. Comparisons of kinetics for 1-octene epoxidation with H 2 O 2 on Ti-BEA and Ti-MFI catalysts with different hydrophilicities in methanol (CH 3 OH) or acetonitrile (CH 3 CN) solvents show the significance of the solvent for stabilizing catalytically-relevant species and the complex interdependencies between solvent, catalyst topology, and hydrophilicity. Epoxidation turnover rates are higher in CH 3 CN than CH 3 OH for Ti-BEA, but the opposite trend is observed for Ti-MFI. Ti-silicates with greater silanol densities, however, give greater epoxidation turnover rates than their hydrophobic counterparts in both solvents. Kinetic, spectroscopic, and thermodynamic analyses show that differences in turnover rates mainly arise from changes in the stabilization of reactive surface species by solvent mediated interactions, because the mechanism of the reaction and stability of the fluid-phase reactants remain similar in CH 3 CN and CH 3 OH. Specifically, apparent activation free energy values ($ΔG^{‡}_{App}$) indicate that surface intermediates responsible for alkene epoxidation are stabilized to a greater extent in CH 3 CN on Ti-BEA and in CH 3 OH on Ti-MFI. Hydrophilic Ti-silicates present lower ($ΔG^{‡}_{App}$) values regardless of solvent identity, which suggests that these differences correspond to the number of hydrogen-bonding solvent molecules found near reactive species bound to Ti active sites. Finally, taken together, these findings demonstrate the role of solvent molecules in allowing reactive intermediates to recognize the properties of active sites beyond the length-scale of covalent bonds, which carry implications for epoxidation but also other reactions within solvent-filled pores of microporous materials.

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

Editors’ Choice—Necessity to Avoid Titanium Oxide as Electrocatalyst Support in PEM Fuel Cells: A Membrane Durability Study

Pt/TiO 2 as electrocatalyst was found to significantly increase the rate of the membrane chemical degradation in a polymer electrolyte membrane (PEM) fuel cell. The increased degradation was proved to be due to TiO x (TiO 2 or Ti 4 O 7 ), which is widely recognized as a promising corrosion-resistant electrocatalyst support. The membrane degradation (thinning) appears to be preferentially in the side facing anode electrode. Migrated Ti species as a result of TiO x dissolution during fuel cell operation in an acidic environment was quantified by electron probe microanalysis (EPMA). Total fluorine inventory loss of the membrane strongly depends on the quantity of migrated Ti species (likely Ti 3+ and/or Ti 4+ ). The membrane chemical degradation induced by TiO x is proposed to be due to dissolved ionic Ti species reacting with H 2 O 2 through a Fenton reaction. TiO x is determined to be inviable as electrocatalyst support for PEM fuel cells, and future research is suggested to be directed toward alternative oxides with similar corrosion-resistance.

08 HYDROGEN↗
DOE OSTI2024

Low pH Titanium Electrochemistry in the Presence of Sulfuric Acid and its Implications for Redox Flow Battery Applications

Titanium (Ti) is a promising elemental redox active species for redox flow batteries (RFBs) due to its 100x availability in the Earth crust, and 10x lower cost (compared to elemental vanadium). Furthermore, Ti salts are highly soluble in water and concentrations >5 M can be easily obtained. Seeking to harness the higher solubility (and hence energy density) of the Ti electrolyte for flow battery applications, the Ti 4+ /Ti 3+ redox couple was investigated at high concentrations (up to 5 M) relevant to RFB applications. The behavior of Ti ions in H 2 SO 4 supported electrolytes was investigated by varying the ratio of Ti redox active species to counterion. The electrochemical characteristics, transport properties, and redox kinetics of the Ti 4+ /Ti 3+ redox couple were measured and the impact of the Ti x+ to solvating ligand ratio was examined. The coordination structures around solvated Ti x+ ions were spectroscopically determined and the effect of solvation structure on the Ti 3+ /Ti 4+ redox rate constants were examined and correlated to the calculated solvation energy (hence distinguishing between inner- and outer-sphere processes) and the role of catalysts was addressed. The Ti electrolyte development guidelines presented herein will advance the development of Ti-based RFBs as a promising pathway towards cost effective, grid-scale energy storage.

Electrochemistry↗
NASA NTRS2022

Atomic-Scale Structure and Non-Stoichiometry of Meteoritic Hibonite: A Transmission Electron Microscope Study

Hibonite (CaAl_12O_19) is a common refractory mineral in Ca-Al-rich inclusions (CAIs) in primitive meteorites. Transmission electron microscope (TEM) studies have identified enigmatic planar defects in different occurrences of hibonite in the Allende meteorite that give rise to strong streaking along c* in electron diffraction patterns. Atomic resolution high-angle annular dark-field (HAADF) imaging and energy-dispersive X-ray (EDX) analyses were used to determine the nature and origin of these planar features. HAADF images of hibonite grains reveal lamellar intergrowths of common 1.6 nm spacing, and less commonly 2.0 and 2.5 nm spacings, interspersed in stoichiometric hibonite showing 1.1 nm (002) spacing. Stoichiometric hibonite consists of alternating Ca-containing (“R”) and spinel-structured (“S”) blocks stacked in a sequence RS. In contrast, the 1.6 nm layers result from a doubled S block such that the stacking sequence is RSS, while in the widest defect observed, the stacking sequence is RSSSS. These intergrowths are epitaxial and have coherent, low-strain boundaries with the host hibonite Meteoritic hibonite shows common Ti and Mg substitution for Al in its structure. Atomic-resolution EDX maps of hibonite grains in the Allende CAI confirm the preferred site occupancy of Mg on tetragonal M3 sites in S blocks and of Ti on trigonal bipyramidal M2 and octahedral M4 sites in R blocks. Mg is highly concentrated, but Ti is absent in the planar defects where wider S blocks show Al-rich compositions compared to stoichiometric MgAl_2O_4 spinel. Therefore, Mg likely played the major role in the formation and metastability of planar defects in hibonite. Electron energy loss spectroscopy data from the Ti L_2,3 edge show the presence of mixed Ti oxidation states with ~ 15–20% of Ti as Ti^(3+) in hibonite, suggesting a direct substitution of Ti^(3+) ↔ Al^(3+) in hibonite. The remaining ~ 80–85% of Ti is present as Ti^(4+) and corresponding EDX analyses are consistent with the well-known coupled substitution 2Al^(3+) ↔ Ti^(4+) + Mg^(2+) being the major mechanism for Ti and Mg substitution in hibonite. The formation of planar defects in hibonite occurred during high-temperature nebular condensation or melting/crystallization processes. The occurrence of non-stoichiometric hibonite in the Allende CAI deviates from the mineral formation sequence predicted from equilibrium condensation models. Overall, our atomic resolution TEM observations signify non-equilibrium, kinetic-controlled crystal growth during the high-temperature formation of refractory solids in the early solar nebula.

hibonite↗
DOE OSTI2020

Materials Data on Ti5Sn3 by Materials Project

Ti5Sn3 crystallizes in the hexagonal P6_3/mcm space group. The structure is three-dimensional. there are two inequivalent Ti sites. In the first Ti site, Ti is bonded in a 5-coordinate geometry to five equivalent Sn atoms. There are a spread of Ti–Sn bond distances ranging from 2.76–2.97 Å. In the second Ti site, Ti is bonded in a 8-coordinate geometry to two equivalent Ti and six equivalent Sn atoms. Both Ti–Ti bond lengths are 2.72 Å. All Ti–Sn bond lengths are 2.84 Å. Sn is bonded in a 9-coordinate geometry to nine Ti atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Y(TiGa2)2 by Materials Project

Y(TiGa2)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Y is bonded in a distorted square co-planar geometry to twelve Ga atoms. There are four shorter (2.90 Å) and eight longer (3.33 Å) Y–Ga bond lengths. Ti is bonded in a 10-coordinate geometry to two equivalent Ti and eight Ga atoms. Both Ti–Ti bond lengths are 2.74 Å. All Ti–Ga bond lengths are 2.80 Å. There are six inequivalent Ga sites. In the first Ga site, Ga is bonded in a 11-coordinate geometry to three equivalent Y, four equivalent Ti, and four Ga atoms. There are two shorter (2.66 Å) and two longer (2.93 Å) Ga–Ga bond lengths. In the second Ga site, Ga is bonded in a 11-coordinate geometry to three equivalent Y, four equivalent Ti, and four Ga atoms. There are one shorter (2.66 Å) and two longer (2.93 Å) Ga–Ga bond lengths. In the third Ga site, Ga is bonded in a 11-coordinate geometry to three equivalent Y, four equivalent Ti, and four Ga atoms. There are one shorter (2.66 Å) and two longer (2.93 Å) Ga–Ga bond lengths. In the fourth Ga site, Ga is bonded in a 11-coordinate geometry to three equivalent Y, four equivalent Ti, and four Ga atoms. Both Ga–Ga bond lengths are 2.66 Å. In the fifth Ga site, Ga is bonded in a 11-coordinate geometry to three equivalent Y, four equivalent Ti, and four Ga atoms. The Ga–Ga bond length is 2.66 Å. In the sixth Ga site, Ga is bonded in a 11-coordinate geometry to three equivalent Y, four equivalent Ti, and four Ga atoms. The Ga–Ga bond length is 2.66 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ti6Si2B by Materials Project

Ti6Si2B crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. there are two inequivalent Ti sites. In the first Ti site, Ti is bonded in a 4-coordinate geometry to two equivalent B and two equivalent Si atoms. Both Ti–B bond lengths are 2.32 Å. Both Ti–Si bond lengths are 2.64 Å. In the second Ti site, Ti is bonded in a 5-coordinate geometry to one B and four equivalent Si atoms. The Ti–B bond length is 2.71 Å. All Ti–Si bond lengths are 2.66 Å. B is bonded in a 9-coordinate geometry to nine Ti atoms. Si is bonded in a 9-coordinate geometry to nine Ti atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ti2InNi2 by Materials Project

Ti2Ni2In crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. there are two inequivalent Ti sites. In the first Ti site, Ti is bonded in a 6-coordinate geometry to six equivalent Ni and four equivalent In atoms. There are four shorter (2.54 Å) and two longer (2.61 Å) Ti–Ni bond lengths. All Ti–In bond lengths are 3.00 Å. In the second Ti site, Ti is bonded in a 6-coordinate geometry to six equivalent Ni and four equivalent In atoms. There are two shorter (2.58 Å) and four longer (2.61 Å) Ti–Ni bond lengths. All Ti–In bond lengths are 3.07 Å. Ni is bonded in a 10-coordinate geometry to six Ti, two equivalent Ni, and two equivalent In atoms. There are one shorter (2.49 Å) and one longer (2.75 Å) Ni–Ni bond lengths. Both Ni–In bond lengths are 2.75 Å. In is bonded in a 12-coordinate geometry to eight Ti, four equivalent Ni, and two equivalent In atoms. Both In–In bond lengths are 3.12 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NaTi2O4 by Materials Project

NaTi2O4 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Na1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Na–O bond distances ranging from 2.39–2.63 Å. There are two inequivalent Ti+3.50+ sites. In the first Ti+3.50+ site, Ti+3.50+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing TiO6 octahedra. The corner-sharing octahedra tilt angles range from 47–54°. There are a spread of Ti–O bond distances ranging from 1.98–2.05 Å. In the second Ti+3.50+ site, Ti+3.50+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing TiO6 octahedra. The corner-sharing octahedra tilt angles range from 47–54°. There are four shorter (2.02 Å) and two longer (2.03 Å) Ti–O bond lengths. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded to two equivalent Na1+ and three equivalent Ti+3.50+ atoms to form a mixture of distorted edge and corner-sharing ONa2Ti3 trigonal bipyramids. In the second O2- site, O2- is bonded in a 5-coordinate geometry to two equivalent Na1+ and three Ti+3.50+ atoms. In the third O2- site, O2- is bonded to two equivalent Na1+ and three equivalent Ti+3.50+ atoms to form a mixture of distorted edge and corner-sharing ONa2Ti3 square pyramids. In the fourth O2- site, O2- is bonded in a 5-coordinate geometry to two equivalent Na1+ and three Ti+3.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ti5Ga3 by Materials Project

Ti5Ga3 crystallizes in the hexagonal P6_3/mcm space group. The structure is three-dimensional. there are two inequivalent Ti sites. In the first Ti site, Ti is bonded in a 5-coordinate geometry to five equivalent Ga atoms. There are a spread of Ti–Ga bond distances ranging from 2.62–2.91 Å. In the second Ti site, Ti is bonded in a 6-coordinate geometry to two equivalent Ti and six equivalent Ga atoms. Both Ti–Ti bond lengths are 2.66 Å. All Ti–Ga bond lengths are 2.69 Å. Ga is bonded in a 9-coordinate geometry to nine Ti atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ti3P by Materials Project

Ti3P crystallizes in the tetragonal P4_2/n space group. The structure is three-dimensional. there are three inequivalent Ti sites. In the first Ti site, Ti is bonded in a distorted bent 150 degrees geometry to two equivalent P atoms. There are one shorter (2.52 Å) and one longer (2.56 Å) Ti–P bond lengths. In the second Ti site, Ti is bonded in a distorted see-saw-like geometry to four equivalent P atoms. There are a spread of Ti–P bond distances ranging from 2.55–2.61 Å. In the third Ti site, Ti is bonded in a 3-coordinate geometry to three equivalent P atoms. There are a spread of Ti–P bond distances ranging from 2.48–2.63 Å. P is bonded in a 9-coordinate geometry to nine Ti atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ti3Co5B2 by Materials Project

Ti3Co5B2 crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. there are two inequivalent Ti sites. In the first Ti site, Ti is bonded in a body-centered cubic geometry to eight equivalent Co atoms. All Ti–Co bond lengths are 2.48 Å. In the second Ti site, Ti is bonded in a 1-coordinate geometry to ten Co and three equivalent B atoms. There are a spread of Ti–Co bond distances ranging from 2.58–2.72 Å. There are one shorter (2.45 Å) and two longer (2.53 Å) Ti–B bond lengths. There are two inequivalent Co sites. In the first Co site, Co is bonded in a 4-coordinate geometry to four equivalent Ti and four equivalent B atoms. All Co–B bond lengths are 2.10 Å. In the second Co site, Co is bonded in a 4-coordinate geometry to six Ti and two equivalent B atoms. Both Co–B bond lengths are 2.08 Å. B is bonded in a 9-coordinate geometry to three equivalent Ti and six Co atoms.

36 MATERIALS SCIENCE↗