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NASA NTRS1988

SSME single-crystal turbine blade dynamics

A study was performrd to determine the dynamic characteristics of the Space Shuttle Main Engine high pressure fuel turbopump (HPFTP) blades made of single crystal (SC) material. The first and second stage drive turbine blades of HPFTP were examined. The nonrotating natural frequencies were determined experimentally and analytically. The experimental results of the SC second stage blade were used to verify the analytical procedures. The study examined the SC first stage blade natural frequencies with respect to crystal orientation at typical operating conditions. The SC blade dynamic response was predicted to be less than the directionally solidified base. Crystal axis orientation optimization indicated that the third mode interference will exist in any SC orientation.

Moss, Larry A.↗

NASA NTRS1990

Electron microscopy study of the iron meteorite Santa Catharina

A characterization of the microstructural features of Santa Catharina (SC) from the millimeter to submicron scale is presented. The same specimen was examined using an optical microscope, a scanning electron microscope, an electron probe microanalyzer, and an analytical electron microscope. Findings include the fact that SC metal nodules may have different bulk Ni values, leading to different microstructures upon cooling; that SC USNM 6293 is the less corroded sample, as tetrataenite exists as less than 10 nm ordered domains throughout the entire fcc matrix (it is noted that this structure is the same as that of the Twin City meteorite and identical to clear taenite II in the retained taenite regions of the octahedrites); that SC USNM 3043 has a more complicated microstructure due to corrosion; and that the low Ni phase of the cloudy zone was selectively corroded in some areas and formed the dark regions, indicating that the SC meteorite corrosion process was electrochemical in nature and may involve Cl-containing akaganeite.

Zhang, J.↗

NASA NTRS1993

Consortium study of lunar meteorites Yamato-793169 and Asuka-881757: Geochemical evidence of mutual similarity, and dissimilarity versus other mare basalts

Compositions of bulk powders and separated minerals from two meteorites derived from the mare lava plains of the Earth's Moon, Yamato-793169 and Asuka-881757, indicate a remarkable degree of similarity to one another, and clearly favor lunar origin. However, these meteorites are unlike any previously studied lunar rock. In both cases, the bulk-rock TiO2 content is slightly greater than the level separating VLT from low-Ti mare basalt, yet the Sc content is much higher than previously observed except among high-Ti mare basalts. Conceivably, the Sc enrichment in A881757 reflects origin of this rock as a cumulate from a mare magma of 'normal' Sc content, but this seems unlikely. Mineral-separate data suggest that most of the Sc is in pyroxene, and a variety of evidence weighs against the cumulus hypothesis as a major cause for the high Sc. The remarkable similarity between Y793169 and A881757 suggests the possibility that they were derived from a single source crater on the Moon.

Warren, Paul H.↗

NASA NTRS1998

Global Warming Estimation From Microwave Sounding Unit

Microwave Sounding Unit (MSU) Ch 2 data sets, collected from sequential, polar-orbiting, Sun-synchronous National Oceanic and Atmospheric Administration operational satellites, contain systematic calibration errors that are coupled to the diurnal temperature cycle over the globe. Since these coupled errors in MSU data differ between successive satellites, it is necessary to make compensatory adjustments to these multisatellite data sets in order to determine long-term global temperature change. With the aid of the observations during overlapping periods of successive satellites, we can determine such adjustments and use them to account for the coupled errors in the long-term time series of MSU Ch 2 global temperature. In turn, these adjusted MSU Ch 2 data sets can be used to yield global temperature trend. In a pioneering study, Spencer and Christy (SC) (1990) developed a procedure to derive the global temperature trend from MSU Ch 2 data. Such a procedure can leave unaccounted residual errors in the time series of the temperature anomalies deduced by SC, which could lead to a spurious long-term temperature trend derived from their analysis. In the present study, we have developed a method that avoids the shortcomings of the SC procedure, the magnitude of the coupled errors is not determined explicitly. Furthermore, based on some assumptions, these coupled errors are eliminated in three separate steps. Such a procedure can leave unaccounted residual errors in the time series of the temperature anomalies deduced by SC, which could lead to a spurious long-term temperature trend derived from their analysis. In the present study, we have developed a method that avoids the shortcomings of the SC procedures. Based on our analysis, we find there is a global warming of 0.23+/-0.12 K between 1980 and 1991. Also, in this study, the time series of global temperature anomalies constructed by removing the global mean annual temperature cycle compares favorably with a similar time series obtained from conventional observations of temperature.

Prabhakara, C.↗

NASA NTRS1998

Angular-Rate Estimation Using Quaternion Measurements

In most spacecraft (SC) there is a need to know the SC angular rate. Precise angular rate is required for attitude determination, and a coarse rate is needed for attitude control damping. Classically, angular rate information is obtained from gyro measurements. These days, there is a tendency to build smaller, lighter and cheaper SC, therefore the inclination now is to do away with gyros and use other means and methods to determine the angular rate. The latter is also needed even in gyro equipped satellites when performing high rate maneuvers whose angular-rate is out of range of the on board gyros or in case of gyro failure. There are several ways to obtain the angular rate in a gyro-less SC. When the attitude is known, one can differentiate the attitude in whatever parameters it is given and use the kinematics equation that connects the derivative of the attitude with the satellite angular-rate and compute the latter. Since SC usually utilize vector measurements for attitude determination, the differentiation of the attitude introduces a considerable noise component in the computed angular-rate vector.

Azor, Ruth↗

NASA NTRS2005

Wave-driven Equatorial Annual Oscillation Induced and Modulated by the Solar Cycle

Our model for the solar cycle (SC) modulation of the Quasi-Biennial Oscillation (QBO) produces a hemispherically symmetric 12-month Annual Oscillation (AO) in the zonal winds, which is confined to low latitudes. This Equatorial Annual Oscillation (EAO) is produced by interaction between the anti-symmetric component of SC forcing and the dominant anti-symmetric AO. The EA0 is amplified by the upward propagating small- scale gravity waves (GW), and the oscillation propagates down through the stratosphere like the QBO. The amplitude of the EA0 is relatively small, but its SC modulation contributes significantly to extend the effect to lower altitudes. Although the energy of the EA0 is concentrated at low latitudes, prominent signatures appear in the Polar Regions where the SC produces measurable temperature variations. At lower altitudes, the SC effects are significantly different in the two hemispheres because of the EAO, and due to its GW driven downward propagation the phase of the annual cycle is delayed.

Mayr, Hans G.↗

NASA NTRS2006

Geochemistry of Pallasite Olivines and the Origin of Main-Group Pallasites

Main-group pallasites (PMG) are mixtures of iron-nickel metal and magnesian olivine thought to have been formed at the core-mantle boundary of an asteroid [1]. Some have anomalous metal compositions (PMG-am) and a few have atypically ferroan olivines (PMG-as) [2]. PMG metal is consistent with an origin as a late fractionate of the IIIAB iron core [2]. Most PMG olivines have very similar Fe/Mg ratios, likely due to subsolidus redox reaction with the metal [3]. In contrast, minor and trace elements show substantial variation, which may be explained by either: (i) PMG were formed at a range of depths in the parent asteroid; the element variations reflect variations in igneous evolution with depth, (ii) the pallasite parent asteroid was chemically heterogeneous; the heterogeneity partially survived igneous processing, or (iii) PMG represent the core-mantle boundaries of several distinct parent asteroids [4, 5]. We have continued doing major, minor and trace elements by EMPA and INAA on a wider suite of PMG olivines, and have begun doing precise oxygen isotope analyses to test these hypotheses. Manganese is homologous with Fe(2+), and can be used to distinguish between magmatic and redox processes as causes for Fe/Mg variations. PMG olivines have a range in molar 1000*Mn/Mg of 2.3-4.6 indicating substantial igneous fractionation in olivines with very similar Fe/Mg (0.138-0.148). The Mg-Mn-Fe distributions can be explained by a fractional crystallization-reduction model; higher Mn/Mg ratios reflect more evolved olivines while Fe/Mg is buffered by redox reactions with the metal. There is a positive association between Mn/Mg and Sc content that is consistent with igneous fractionation. However, most PMG olivines fall within a narrow Mn/Mg range (3.0-3.6), but these show a substantial range in Sc (1.00-2.29 micro-g/g). Assuming fractional crystallization, this Sc range could have resulted from approx.65% crystallization of an ultramafic magma. This is inconsistent with formation at the core-mantle boundary of a single asteroid [4]. One alternative is that the PMG are fragments of several asteroids, and these could have had different initial Sc contents, Mn/Mg and differences in igneous history. Our preliminary O isotope data and those of [6, 7] do not support this, although the coverage of PMG olivines is incomplete. The PMG-as Springwater is not easily fit in any scenario. Its olivine has among the highest Mn/Mg suggesting it is one of the most evolved, but the lowest Sc content suggesting it is the least evolved. The O isotopic composition of Springwater olivine is the same as that of other PMG. Thus there is no indication that it represents a distinct parent asteroid. Our preliminary O isotopic data favor a single PMG parent asteroid. In this case, the olivines are more likely melt-residues, and that the parent asteroid was initially heterogeneous in chemical, but not isotopic, composition.

Mittlefehldt, D. W.↗

NASA NTRS2017

Static Measurements on HTS Coils of Fully Superconducting AC Electric Machines for Aircraft Electric Propulsion System

The NASA Glenn Research Center (GRC) has been developing the high efficiency and high-power density superconducting (SC) electric machines in full support of electrified aircraft propulsion (EAP) systems for a future electric aircraft. A SC coil test rig has been designed and built to perform static and AC measurements on BSCCO, (RE)BCO, and YBCO high temperature superconducting (HTS) wire and coils at liquid nitrogen (LN2) temperature. In this paper, DC measurements on five SC coil configurations of various geometry in zero external magnetic field are measured to develop good measurement technique and to determine the critical current (Ic) and the sharpness (n value) of the super-to-normal transition. Also, standard procedures for coil design, fabrication, coil mounting, micro-volt measurement, cryogenic testing, current control, and data acquisition technique were established. Experimentally measured critical currents are compared with theoretical predicted values based on an electric-field criterion (Ec). Data here are essential to quantify the SC electric machine operation limits where the SC begins to exhibit non-zero resistance. All test data will be utilized to assess the feasibility of using HTS coils for the fully superconducting AC electric machine development for an aircraft electric propulsion system.

superconducting motor↗

NASA NTRS2023

Spacecraft Floating Potential Measurements for the Wind Spacecraft

Analysis of 8,804,545 electron velocity distribution functions, observed by the Wind spacecraft near 1 au between 2005 January 1 and 2022 January 1, was performed to determine the spacecraft floating potential, ∅ sc . Wind was designed to be electrostatically clean, which helps keep the magnitude of ∅ sc small (i.e., ∼5–9 eV for nearly all intervals) and the potential distribution more uniform. We observed spectral enhancements of ∅ sc at frequencies corresponding to the inverse synodic Carrington rotation period with at least three harmonics. The two-dimensional histogram of ∅ sc versus time also shows at least two strong peaks, with a potential third, much weaker peak. These peaks vary in time, with the intensity correlated with solar maximum. Thus, the spectral peaks and histogram peaks are likely due to macroscopic phenomena like coronal mass ejections (solar cycle dependence) and stream interaction regions (Carrington rotation dependence). The values of ∅ sc are summarized herein and the resulting data set is discussed.

Lynn B Wilson III↗

DOE OSTI2024

Dopant Segregation in Single-Crystal Optical Fiber Grown via the Laser-Heated Pedestal Growth Technique

Single crystal (SC) optical fiber has promising potential to be used for optical fiber sensing applications in harsh conditions due to its robustness to high temperature, high radioactivity, and resistance to chemical corrosion as compared to optical sensors using silica fiber. However, SC fiber grown via the laser-heated pedestal growth (LHPG) technique innately does not have a core-cladding structure found in standard optical fiber, resulting in optical losses. In this work we investigate optimization of the growth parameters of a two LHPG process used to grow SC fiber with a graded index via introduction of dopants to the feedstock material. Feedstock material is fabricated with the first LHPG device, then sol-gel dip-coated to create outer films of dopant material. The dip-coated feedstock is used to grow SC fiber in which segregation of the dopant constituents occurs, resulting in a graded index of refraction across the fiber, and an effective core-cladding structure. Hardware and software improvements to both LHPG systems are presented and the growth parameters for short pieces of ~320-330 μm diameter YAG fiber has been established. Characterization techniques/procedures have also been established for future grown SC fiber. These improvements and preparations are anticipated to result in a significant increase in grown fiber quality with a similar growth rate to that previously established.

Lander, Gary↗

DOE OSTI2024

Dopant Segregation in Single-Crystal Optical Fiber Grown via the Laser-Heated Pedestal Growth Technique

Lander, Gary↗

DOE OSTI2025

Efficient CO2 and Natural Gas Refinery for Ethylene Production - Catalyst Development for Oxidative Coupling of Methane (OCM)

We designed a new electro-catalyst for oxidative coupling of methane (OCM) reaction, the structure of the Sc doped La0.3Sr0.7TiO3-d (LaSrTi) Sc doping to LaSrTi leading to lattice expansion and more distorted lattice, Investigated the effect of doping on the oxygen vacancy formation energy DFT calculations shows that Sc doping facilitate oxygen vacancy formation. Quantifying the surface basicity of the sample before and after Sc doping Sc doped sample exhibits high surface basicity.

catalysis↗

DOE OSTI2020

Materials Data on ScGe2 by Materials Project

ScGe2 is Zirconium Disilicide structured and crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Sc is bonded in a 10-coordinate geometry to ten Ge atoms. There are a spread of Sc–Ge bond distances ranging from 2.81–3.08 Å. There are two inequivalent Ge sites. In the first Ge site, Ge is bonded in a 4-coordinate geometry to six equivalent Sc and two equivalent Ge atoms. Both Ge–Ge bond lengths are 2.62 Å. In the second Ge site, Ge is bonded in a 8-coordinate geometry to four equivalent Sc and four equivalent Ge atoms. All Ge–Ge bond lengths are 2.75 Å.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on ScRe2 by Materials Project

ScRe2 is Hexagonal Laves structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Sc is bonded in a 12-coordinate geometry to twelve Re atoms. There are a spread of Sc–Re bond distances ranging from 3.07–3.11 Å. There are two inequivalent Re sites. In the first Re site, Re is bonded to six equivalent Sc and six equivalent Re atoms to form a mixture of face, edge, and corner-sharing ReSc6Re6 cuboctahedra. All Re–Re bond lengths are 2.67 Å. In the second Re site, Re is bonded to six equivalent Sc and six Re atoms to form a mixture of face, edge, and corner-sharing ReSc6Re6 cuboctahedra. There are two shorter (2.57 Å) and two longer (2.73 Å) Re–Re bond lengths.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on RbScAsO4F by Materials Project

RbScAsO4F crystallizes in the orthorhombic Pna2_1 space group. The structure is three-dimensional. there are two inequivalent Rb1+ sites. In the first Rb1+ site, Rb1+ is bonded in a 9-coordinate geometry to seven O2- and two F1- atoms. There are a spread of Rb–O bond distances ranging from 2.89–3.33 Å. There are one shorter (2.95 Å) and one longer (3.35 Å) Rb–F bond lengths. In the second Rb1+ site, Rb1+ is bonded in a 8-coordinate geometry to six O2- and two F1- atoms. There are a spread of Rb–O bond distances ranging from 2.89–3.31 Å. There are one shorter (2.93 Å) and one longer (3.24 Å) Rb–F bond lengths. There are two inequivalent Sc3+ sites. In the first Sc3+ site, Sc3+ is bonded to four O2- and two F1- atoms to form ScO4F2 octahedra that share corners with two equivalent ScO4F2 octahedra and corners with four AsO4 tetrahedra. The corner-sharing octahedral tilt angles are 48°. There are a spread of Sc–O bond distances ranging from 2.03–2.14 Å. There are one shorter (2.12 Å) and one longer (2.15 Å) Sc–F bond lengths. In the second Sc3+ site, Sc3+ is bonded to four O2- and two F1- atoms to form ScO4F2 octahedra that share corners with two equivalent ScO4F2 octahedra and corners with four AsO4 tetrahedra. The corner-sharing octahedral tilt angles are 48°. There are a spread of Sc–O bond distances ranging from 2.08–2.16 Å. There are one shorter (2.07 Å) and one longer (2.10 Å) Sc–F bond lengths. There are two inequivalent As5+ sites. In the first As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with four ScO4F2 octahedra. The corner-sharing octahedra tilt angles range from 40–50°. There are a spread of As–O bond distances ranging from 1.71–1.73 Å. In the second As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with four ScO4F2 octahedra. The corner-sharing octahedra tilt angles range from 45–49°. There is one shorter (1.71 Å) and three longer (1.72 Å) As–O bond length. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to two Rb1+, one Sc3+, and one As5+ atom. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to one Sc3+ and one As5+ atom. In the third O2- site, O2- is bonded in a 2-coordinate geometry to two Rb1+, one Sc3+, and one As5+ atom. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to two Rb1+, one Sc3+, and one As5+ atom. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to two Rb1+, one Sc3+, and one As5+ atom. In the sixth O2- site, O2- is bonded in a 2-coordinate geometry to two Rb1+, one Sc3+, and one As5+ atom. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to one Rb1+, one Sc3+, and one As5+ atom. In the eighth O2- site, O2- is bonded in a 2-coordinate geometry to two Rb1+, one Sc3+, and one As5+ atom. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded in a 2-coordinate geometry to two Rb1+ and two Sc3+ atoms. In the second F1- site, F1- is bonded in a 2-coordinate geometry to two Rb1+ and two Sc3+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on ScH3Br3N by Materials Project

ScNH3Br3 crystallizes in the triclinic P-1 space group. The structure is one-dimensional and consists of one ScNH3Br3 ribbon oriented in the (1, 1, -1) direction. there are two inequivalent Sc3+ sites. In the first Sc3+ site, Sc3+ is bonded to one N3- and five Br1- atoms to form edge-sharing ScBr5N octahedra. The Sc–N bond length is 2.29 Å. There are a spread of Sc–Br bond distances ranging from 2.55–2.76 Å. In the second Sc3+ site, Sc3+ is bonded to one N3- and five Br1- atoms to form edge-sharing ScBr5N octahedra. The Sc–N bond length is 2.29 Å. There are a spread of Sc–Br bond distances ranging from 2.55–2.75 Å. There are two inequivalent N3- sites. In the first N3- site, N3- is bonded in a distorted trigonal non-coplanar geometry to one Sc3+ and three H1+ atoms. All N–H bond lengths are 1.03 Å. In the second N3- site, N3- is bonded in a distorted trigonal non-coplanar geometry to one Sc3+ and three H1+ atoms. All N–H bond lengths are 1.03 Å. There are six inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the second H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the third H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. There are six inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in an L-shaped geometry to two Sc3+ atoms. In the second Br1- site, Br1- is bonded in a water-like geometry to two equivalent Sc3+ atoms. In the third Br1- site, Br1- is bonded in an L-shaped geometry to two Sc3+ atoms. In the fourth Br1- site, Br1- is bonded in an L-shaped geometry to two equivalent Sc3+ atoms. In the fifth Br1- site, Br1- is bonded in a single-bond geometry to one Sc3+ atom. In the sixth Br1- site, Br1- is bonded in a single-bond geometry to one Sc3+ atom.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on ScH3NCl3 by Materials Project

ScNH3Cl3 crystallizes in the triclinic P-1 space group. The structure is one-dimensional and consists of one ScNH3Cl3 ribbon oriented in the (1, 1, -1) direction. there are two inequivalent Sc3+ sites. In the first Sc3+ site, Sc3+ is bonded to one N3- and five Cl1- atoms to form edge-sharing ScNCl5 octahedra. The Sc–N bond length is 2.28 Å. There are a spread of Sc–Cl bond distances ranging from 2.39–2.59 Å. In the second Sc3+ site, Sc3+ is bonded to one N3- and five Cl1- atoms to form edge-sharing ScNCl5 octahedra. The Sc–N bond length is 2.28 Å. There are a spread of Sc–Cl bond distances ranging from 2.39–2.59 Å. There are two inequivalent N3- sites. In the first N3- site, N3- is bonded in a distorted trigonal non-coplanar geometry to one Sc3+ and three H1+ atoms. All N–H bond lengths are 1.03 Å. In the second N3- site, N3- is bonded in a distorted trigonal non-coplanar geometry to one Sc3+ and three H1+ atoms. All N–H bond lengths are 1.03 Å. There are six inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the second H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the third H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. There are six inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a water-like geometry to two Sc3+ atoms. In the second Cl1- site, Cl1- is bonded in a water-like geometry to two equivalent Sc3+ atoms. In the third Cl1- site, Cl1- is bonded in a single-bond geometry to one Sc3+ atom. In the fourth Cl1- site, Cl1- is bonded in a single-bond geometry to one Sc3+ atom. In the fifth Cl1- site, Cl1- is bonded in an L-shaped geometry to two equivalent Sc3+ atoms. In the sixth Cl1- site, Cl1- is bonded in an L-shaped geometry to two Sc3+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Sc5(Re2Si3)4 by Materials Project

Sc5(Re2Si3)4 crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. there are four inequivalent Sc3+ sites. In the first Sc3+ site, Sc3+ is bonded in a 8-coordinate geometry to eight Si+3.33- atoms. There are a spread of Sc–Si bond distances ranging from 2.82–3.15 Å. In the second Sc3+ site, Sc3+ is bonded in a 8-coordinate geometry to eight Si+3.33- atoms. There are a spread of Sc–Si bond distances ranging from 2.61–2.94 Å. In the third Sc3+ site, Sc3+ is bonded in a 8-coordinate geometry to eight Si+3.33- atoms. There are a spread of Sc–Si bond distances ranging from 2.79–3.03 Å. In the fourth Sc3+ site, Sc3+ is bonded in a 8-coordinate geometry to eight Si+3.33- atoms. There are a spread of Sc–Si bond distances ranging from 2.70–2.90 Å. There are six inequivalent Re+3.12+ sites. In the first Re+3.12+ site, Re+3.12+ is bonded in a 7-coordinate geometry to seven Si+3.33- atoms. There are a spread of Re–Si bond distances ranging from 2.39–2.76 Å. In the second Re+3.12+ site, Re+3.12+ is bonded in a distorted hexagonal planar geometry to six Si+3.33- atoms. There are a spread of Re–Si bond distances ranging from 2.48–2.56 Å. In the third Re+3.12+ site, Re+3.12+ is bonded in a 7-coordinate geometry to seven Si+3.33- atoms. There are a spread of Re–Si bond distances ranging from 2.51–2.88 Å. In the fourth Re+3.12+ site, Re+3.12+ is bonded to six Si+3.33- atoms to form a mixture of distorted edge, face, and corner-sharing ReSi6 octahedra. The corner-sharing octahedra tilt angles range from 44–49°. There are a spread of Re–Si bond distances ranging from 2.47–2.55 Å. In the fifth Re+3.12+ site, Re+3.12+ is bonded to six Si+3.33- atoms to form distorted corner-sharing ReSi6 octahedra. The corner-sharing octahedral tilt angles are 44°. There are a spread of Re–Si bond distances ranging from 2.43–2.66 Å. In the sixth Re+3.12+ site, Re+3.12+ is bonded in a 6-coordinate geometry to six Si+3.33- atoms. There are a spread of Re–Si bond distances ranging from 2.44–2.70 Å. There are nine inequivalent Si+3.33- sites. In the first Si+3.33- site, Si+3.33- is bonded in a 10-coordinate geometry to four Sc3+, four Re+3.12+, and two equivalent Si+3.33- atoms. Both Si–Si bond lengths are 2.63 Å. In the second Si+3.33- site, Si+3.33- is bonded in a 3-coordinate geometry to three Sc3+, four Re+3.12+, and four Si+3.33- atoms. There are a spread of Si–Si bond distances ranging from 2.75–2.79 Å. In the third Si+3.33- site, Si+3.33- is bonded in a 10-coordinate geometry to four Sc3+, four Re+3.12+, and two Si+3.33- atoms. The Si–Si bond length is 2.54 Å. In the fourth Si+3.33- site, Si+3.33- is bonded in a 9-coordinate geometry to three Sc3+, four Re+3.12+, and two equivalent Si+3.33- atoms. Both Si–Si bond lengths are 2.54 Å. In the fifth Si+3.33- site, Si+3.33- is bonded in a 10-coordinate geometry to four Sc3+, four Re+3.12+, and two Si+3.33- atoms. The Si–Si bond length is 2.78 Å. In the sixth Si+3.33- site, Si+3.33- is bonded in a 1-coordinate geometry to three Sc3+, four Re+3.12+, and two equivalent Si+3.33- atoms. In the seventh Si+3.33- site, Si+3.33- is bonded in a 11-coordinate geometry to two equivalent Sc3+, five Re+3.12+, and four Si+3.33- atoms. Both Si–Si bond lengths are 2.89 Å. In the eighth Si+3.33- site, Si+3.33- is bonded in a 1-coordinate geometry to three Sc3+, four Re+3.12+, and three Si+3.33- atoms. The Si–Si bond length is 2.50 Å. In the ninth Si+3.33- site, Si+3.33- is bonded in a 8-coordinate geometry to two equivalent Sc3+, five Re+3.12+, and one Si+3.33- atom.

36 MATERIALS SCIENCE↗