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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Ca(HO)2 by Materials Project

Ca(OH)2 crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one Ca(OH)2 sheet oriented in the (0, 0, 1) direction. Ca2+ is bonded to six equivalent O2- atoms to form edge-sharing CaO6 octahedra. All Ca–O bond lengths are 2.39 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 Ca2+ and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(HO)2 by Materials Project

Ca(OH)2 crystallizes in the triclinic P1 space group. The structure is two-dimensional and consists of one Ca(OH)2 sheet oriented in the (0, 0, 1) direction. Ca2+ is bonded to six O2- atoms to form edge-sharing CaO6 octahedra. There are a spread of Ca–O bond distances ranging from 2.37–2.41 Å. There are two 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 0.97 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to three equivalent Ca2+ and one H1+ atom. In the second O2- site, O2- is bonded in a distorted single-bond geometry to three equivalent Ca2+ and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(HO)2 by Materials Project

Ca(OH)2 crystallizes in the trigonal P3m1 space group. The structure is two-dimensional and consists of one Ca(OH)2 sheet oriented in the (0, 0, 1) direction. Ca2+ is bonded in a distorted q6 geometry to three equivalent H1+ and six O2- atoms. All Ca–H bond lengths are 2.24 Å. There are three shorter (2.38 Å) and three longer (2.48 Å) Ca–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 Ca2+ and 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 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 Ca2+ and one H1+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to three equivalent Ca2+ and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(HO)2 by Materials Project

Ca(OH)2 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Ca2+ is bonded in a 7-coordinate geometry to two equivalent H1+ and seven O2- atoms. There are one shorter (2.44 Å) and one longer (2.62 Å) Ca–H bond lengths. There are a spread of Ca–O bond distances ranging from 2.37–2.64 Å. There are two 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 two equivalent Ca2+ and one O2- atom. The H–O bond length is 0.99 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to three equivalent Ca2+ and one H1+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to four equivalent Ca2+ and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Structure and thermodynamics of calcium rare earth silicate oxyapatites, Ca 2 RE 8 (SiO 4 ) 6 O 2 (RE = Pr, Tb, Ho, Tm)

Calcium rare earth silicate oxyapatites, (Ca 2 RE 8 (SiO 4 ) 6 O 2 ), are of interest as components of glass-ceramic nuclear waste forms. To assess their long-term behavior in a geologic repository, it is essential to determine their structure and thermodynamic stability at relevant conditions. Here, in this work, we performed detailed structural and thermodynamic investigations on Ca 2 Pr 8 (SiO 4 ) 6 O 2 , Ca 2 Tb 8 (SiO 4 ) 6 O 2 , Ca 2 Ho 8 (SiO 4 ) 6 O 2 , and Ca 2 Tm 8 (SiO 4 ) 6 O 2 by high energy synchrotron powder X-ray diffraction combined with Rietveld analysis and high temperature oxide melt drop solution calorimetry. Enthalpies of formation from constituent oxides (ΔH f,ox ) were determined to be -765.1 ± 22.8 kJ/mol for Ca 2 Pr 8 (SiO 4 ) 6 O 2 ; -638.9 ± 20.5 kJ/mol for Ca 2 Tb 8 (SiO 4 ) 6 O 2 ; -643.3 ± 10.3 kJ/mol for Ca 2 Ho 8 (SiO 4 ) 6 O 2 ; and -403.2 ± 5.1 kJ/mol for Ca 2 Tm 8 (SiO 4 ) 6 O 2 . These thermodynamic parameters were used in assessing the thermochemical stability of these phases in the presence of water vapor from room temperature to 600 K, as encountered in the subsurface environments of a geological repository.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Syntheses and Crystal Structures of Rare-Earth Oxyapatites Ca 2 RE 8 (SiO 4 ) 6 O 2 (RE = Pr, Tb, Ho, Tm)

Four different rare-earth oxyapatites of Ca 2 RE 8 (SiO 4 ) 6 O 2 (RE = Pr, Tb, Ho, Tm) were synthesized using a solution-based method followed by drying, calcination, and high-temperature sintering in air. X-ray powder diffraction and Raman spectroscopy were performed on the synthesized oxyapatites. Here, the RE oxyapatites crystallize in the hexagonal space group P6 3 /m with similar unit cell parameters, increasing linearly with larger RE cations. The unit cell volumes increase linearly whereas the densities decrease nonlinearly with larger RE cations. Raman spectra showed intense bands of the symmetric bending and stretching modes of SiO 4 at ~ 400 and 860 cm -1 regions, respectively. The bands generally shifted to higher frequencies with smaller RE cations in the structures.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Crystal chemistry and phase equilibria of the CaO-½Ho 2 O 3 -CoO z system at 885 °C in air

Ini this work, the phase equilibrium diagram of the CaO-½Ho 2 O 3 -CoO z system was determined at 885 °C in air. This diagram offers compatibility relationships in the ternary oxide system that are essential for processing and for the understanding of properties of several thermoelectric phases in the system. Four three-phase regions and three solid solution tie-line regions were determined in the CaO-½Ho 2 O 3 -CoO z system. In the CaO-Ho 2 O 3 system, while a small solid solution region was identified for (Ho 1-x Ca x )O (3-z)/2 (0 ≤x ≤ 0.14), Ho was not present in the Ca site of CaO. Neither the reported Ho2CoO4 phase in the Ho 2 O-CoO z system nor the Ca-doped (Ho 1+x Ca1-x)CoO 4-z phase was present at 885 °C. No solid solution of the distorted perovskite, (Ho 1-x Cax)CoO 3-z , was established at this temperature. The CaO-CoO z system consists of two calcium cobaltate thermoelectric compounds. The 2D thermoelectric oxide, (Ca 3-x Ho x )Co 4 O 9-z (0 ≤x ≤ 0.5), has a misfit layered structure, and the 1D Ca 3 Co 2 O 6 consists of chains of alternating CoO 6 trigonal prisms and CoO 6 octahedra. Ca 3 Co 2 O 6 was found to be a stoichiometric compound. A comparison of the phase diagrams of the CaO -½ R 2 O 3 -CoO z (R = La, Nd, Eu, and Ho) systems is given.

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

Kinetic studies of excited singlet oxygen atom O( 1 D) reactions with ethanol

In this work, themultichannel reaction of excited singlet oxygen atom with ethanol, O( 1 D) + C 2 H 5 OH (1), was studied in a photolysis flow reactor coupled with mid-infrared Faraday rotation spectroscopy (FRS) and UV-IR direct absorption spectroscopy (DAS) at 297 K with reactor pressures of 60, 120, and 150 Torr (bath He). The excited singlet oxygen atom was generated through the photolysis of O 3 at 266 nm. The photon flux and O( 1 D) concentrations were determined by in situ actinometry based on O 3 depletion. Temporal profiles of OH and H 2 O were monitored via DAS signals at ca. 3568.62 and 3568.29 cm –1 , while temporal profiles of HO 2 were measured via FRS signals at ca. 1396.90 cm –1 . The branching ratios of the target reaction (1) were determined by fitting temporal profiles to simulations from an in-house reaction mechanism. Two major reaction channels were identified as CH 3 CHOH + OH and CH 3 O + CH 2 OH, and their branching ratios were determined as 0.46 ± 0.12 and 0.42 ± 0.11, respectively. A specific HO 2 + RO 2 reaction between HO 2 and O 2 CH 2 CH 2 OH (β-RO 2 ) at the low-temperature range is estimated in this work as HO 2 + O 2 CH 2 CH 2 OH → products with a rate constant of 7 × 10 –12 cm 3 molecule –1 s –1 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Materials Data on Ca(HoTe2)2 by Materials Project

Ca(HoTe2)2 crystallizes in the monoclinic P2/m space group. The structure is three-dimensional. Ca2+ is bonded to six Te2- atoms to form CaTe6 octahedra that share corners with six equivalent HoTe6 octahedra, edges with two equivalent CaTe6 octahedra, and edges with six HoTe6 octahedra. The corner-sharing octahedra tilt angles range from 2–3°. There are two shorter (3.15 Å) and four longer (3.20 Å) Ca–Te bond lengths. There are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to six Te2- atoms to form HoTe6 octahedra that share corners with six equivalent CaTe6 octahedra, edges with two equivalent CaTe6 octahedra, and edges with six HoTe6 octahedra. The corner-sharing octahedra tilt angles range from 2–3°. There are two shorter (3.03 Å) and four longer (3.10 Å) Ho–Te bond lengths. In the second Ho3+ site, Ho3+ is bonded to six Te2- atoms to form HoTe6 octahedra that share edges with four equivalent CaTe6 octahedra and edges with six HoTe6 octahedra. There are four shorter (3.09 Å) and two longer (3.11 Å) Ho–Te bond lengths. There are two inequivalent Te2- sites. In the first Te2- site, Te2- is bonded to two equivalent Ca2+ and three Ho3+ atoms to form a mixture of edge and corner-sharing TeCa2Ho3 square pyramids. In the second Te2- site, Te2- is bonded in a rectangular see-saw-like geometry to one Ca2+ and three Ho3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CaP2(HO)4 by Materials Project

Ca(H2PO2)2 crystallizes in the monoclinic C2/c space group. The structure is two-dimensional and consists of two Ca(H2PO2)2 sheets oriented in the (1, 0, 0) direction. Ca2+ is bonded to six O2- atoms to form distorted CaO6 octahedra that share corners with six equivalent PH2O2 tetrahedra and edges with two equivalent CaO6 octahedra. There are two shorter (2.30 Å) and four longer (2.42 Å) Ca–O bond lengths. P1+ is bonded to two H1+ and two O2- atoms to form distorted PH2O2 tetrahedra that share corners with three equivalent CaO6 octahedra. The corner-sharing octahedra tilt angles range from 29–54°. Both P–H bond lengths are 1.42 Å. There is one shorter (1.51 Å) and one longer (1.54 Å) P–O bond length. There are two inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one P1+ atom. In the second H1+ site, H1+ is bonded in a single-bond geometry to one P1+ atom. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ca2+ and one P1+ atom. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to one Ca2+ and one P1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CaB2(HO)8 by Materials Project

Ca(B(OH)4)2 crystallizes in the triclinic P-1 space group. The structure is two-dimensional and consists of one Ca(B(OH)4)2 sheet oriented in the (0, 1, 1) direction. Ca2+ is bonded in a 9-coordinate geometry to one H1+ and eight O2- atoms. The Ca–H bond length is 2.61 Å. There are a spread of Ca–O bond distances ranging from 2.39–2.70 Å. There are two inequivalent B3+ sites. In the first B3+ site, B3+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of B–O bond distances ranging from 1.48–1.51 Å. In the second B3+ site, B3+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of B–O bond distances ranging from 1.47–1.52 Å. There are eight 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 1.00 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 single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the fourth 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 fifth 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 sixth 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 seventh H1+ site, H1+ is bonded in a single-bond geometry to one Ca2+ and one O2- atom. The H–O bond length is 0.98 Å. In the eighth 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 eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted water-like geometry to one Ca2+, one B3+, and one H1+ atom. In the second O2- site, O2- is bonded in a distorted water-like geometry to one Ca2+, one B3+, and one H1+ atom. In the third O2- site, O2- is bonded in a 2-coordinate geometry to one Ca2+, one B3+, and one H1+ atom. In the fourth O2- site, O2- is bonded in a distorted water-like geometry to one Ca2+, one B3+, and one H1+ atom. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Ca2+, one B3+, and one H1+ atom. In the sixth O2- site, O2- is bonded in a 2-coordinate geometry to one Ca2+, one B3+, and one H1+ atom. In the seventh O2- site, O2- is bonded in a distorted water-like geometry to one Ca2+, one B3+, and one H1+ atom. In the eighth O2- site, O2- is bonded in a distorted water-like geometry to one B3+ and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CaB2(HO)8 by Materials Project

Ca(B(OH)4)2 crystallizes in the triclinic P-1 space group. The structure is two-dimensional and consists of one Ca(B(OH)4)2 sheet oriented in the (0, 1, 1) direction. Ca2+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ca–O bond distances ranging from 2.39–2.65 Å. There are two inequivalent B3+ sites. In the first B3+ site, B3+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of B–O bond distances ranging from 1.48–1.50 Å. In the second B3+ site, B3+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of B–O bond distances ranging from 1.48–1.51 Å. There are eight 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 0.99 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the third 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 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 0.98 Å. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.97 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. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted water-like geometry to one Ca2+, one B3+, and one H1+ atom. In the second O2- site, O2- is bonded in a distorted water-like geometry to one Ca2+, one B3+, and one H1+ atom. In the third O2- site, O2- is bonded in a 2-coordinate geometry to one Ca2+, one B3+, and one H1+ atom. In the fourth O2- site, O2- is bonded in a distorted water-like geometry to one Ca2+, one B3+, and one H1+ atom. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Ca2+, one B3+, and one H1+ atom. In the sixth O2- site, O2- is bonded in a 2-coordinate geometry to one Ca2+, one B3+, and one H1+ atom. In the seventh O2- site, O2- is bonded in a distorted water-like geometry to one Ca2+, one B3+, and one H1+ atom. In the eighth O2- site, O2- is bonded in a distorted water-like geometry to one B3+ and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(HoSe2)2 by Materials Project

Ca(HoSe2)2 crystallizes in the monoclinic P2/m space group. The structure is three-dimensional. Ca2+ is bonded to six Se2- atoms to form CaSe6 octahedra that share corners with six equivalent HoSe6 octahedra, edges with two equivalent CaSe6 octahedra, and edges with six HoSe6 octahedra. The corner-sharing octahedra tilt angles range from 2–5°. There are two shorter (2.95 Å) and four longer (3.00 Å) Ca–Se bond lengths. There are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to six Se2- atoms to form HoSe6 octahedra that share edges with four equivalent CaSe6 octahedra and edges with six HoSe6 octahedra. There are four shorter (2.86 Å) and two longer (2.87 Å) Ho–Se bond lengths. In the second Ho3+ site, Ho3+ is bonded to six Se2- atoms to form HoSe6 octahedra that share corners with six equivalent CaSe6 octahedra, edges with two equivalent CaSe6 octahedra, and edges with six HoSe6 octahedra. The corner-sharing octahedra tilt angles range from 2–5°. There are two shorter (2.82 Å) and four longer (2.89 Å) Ho–Se bond lengths. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a rectangular see-saw-like geometry to one Ca2+ and three Ho3+ atoms. In the second Se2- site, Se2- is bonded to two equivalent Ca2+ and three Ho3+ atoms to form a mixture of corner and edge-sharing SeCa2Ho3 square pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(HoS2)2 by Materials Project

Ca(HoS2)2 crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Ca2+ is bonded in a 8-coordinate geometry to eight equivalent S2- atoms. There are four shorter (2.80 Å) and four longer (3.05 Å) Ca–S bond lengths. Ho3+ is bonded to eight equivalent S2- atoms to form a mixture of distorted face, edge, and corner-sharing HoS8 hexagonal bipyramids. There are a spread of Ho–S bond distances ranging from 2.74–3.01 Å. S2- is bonded in a 6-coordinate geometry to two equivalent Ca2+ and four equivalent Ho3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(HoS2)2 by Materials Project

Ca(HoS2)2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ca2+ is bonded to seven S2- atoms to form distorted CaS7 pentagonal bipyramids that share corners with eight HoS6 octahedra, edges with five HoS6 octahedra, edges with two equivalent CaS7 pentagonal bipyramids, and faces with two equivalent CaS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 14–67°. There are a spread of Ca–S bond distances ranging from 2.89–3.02 Å. There are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with three equivalent HoS6 octahedra, corners with four equivalent CaS7 pentagonal bipyramids, edges with six HoS6 octahedra, and an edgeedge with one CaS7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 52–60°. There are a spread of Ho–S bond distances ranging from 2.70–2.81 Å. In the second Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with three equivalent HoS6 octahedra, corners with four equivalent CaS7 pentagonal bipyramids, edges with four HoS6 octahedra, and edges with four equivalent CaS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 52–60°. There are a spread of Ho–S bond distances ranging from 2.70–2.78 Å. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded to two equivalent Ca2+ and three Ho3+ atoms to form a mixture of distorted edge and corner-sharing SCa2Ho3 trigonal bipyramids. In the second S2- site, S2- is bonded to two equivalent Ca2+ and three Ho3+ atoms to form SCa2Ho3 square pyramids that share corners with two equivalent SCa3Ho2 square pyramids, corners with two equivalent SCa2Ho3 trigonal bipyramids, edges with five SCa2Ho3 square pyramids, and edges with three equivalent SCa2Ho3 trigonal bipyramids. In the third S2- site, S2- is bonded to three equivalent Ca2+ and two equivalent Ho3+ atoms to form a mixture of edge and corner-sharing SCa3Ho2 square pyramids. In the fourth S2- site, S2- is bonded in a rectangular see-saw-like geometry to four Ho3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Magnetic and Magnetocaloric Properties of the A 2 LnSbO 6 Lanthanide Oxides on the Frustrated fcc Lattice

Frustrated lanthanide oxides are promising candidates for cryogen-free magnetic refrigeration due to their suppressed ordering temperatures and high magnetic moments. While much attention has been paid to the garnet and pyrochlore lattices, the magnetocaloric effect in frustrated face-centered cubic (fcc) lattices remains relatively unexplored. We previously showed that the frustrated fcc double perovskite Ba 2 GdSbO 6 is a top-performing magnetocaloric material (per mol Gd) because of its small nearest-neighbor interaction between spins. Here we investigate different tuning parameters to maximize the magnetocaloric effect in the family of fcc lanthanide oxides, A 2 LnSbO 6 (A = {Ba 2+ , Sr 2+ } and Ln = {Nd 3+ , Tb 3+ , Gd 3+ , Ho 3+ , Dy 3+ , Er 3+ }), including chemical pressure via the A site cation and the magnetic ground state via the lanthanide ion. Bulk magnetic measurements indicate a possible trend between magnetic short-range fluctuations and the field-temperature phase space of the magnetocaloric effect, determined by whether an ion is a Kramers or a non-Kramers ion. We report for the first time on the synthesis and magnetic characterization of the Ca 2 LnSbO 6 series with tunable site disorder that can be used to control the deviations from Curie–Weiss behavior. Taken together, these results suggest fcc lanthanide oxides as tunable systems for magnetocaloric design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2012

Metasomatic Control of Water in Garnet and Pyroxene from Kaapvaal Craton Mantle Xenoliths

Fourier transform infrared spectrometry (FTIR) and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) were used to determine water, rare earth (REE), lithophile (LILE), and high field strength (HFSE) element contents in garnet and pyroxene from mantle xenoliths, Kaapvaal craton, southern Africa. Water enters these nominally anhydrous minerals as protons bonded to structural oxygen in lattice defects. Pyroxene water contents (150-400 ppm in clinopyroxene; 40-250 ppm in orthopyroxene) correlate with their Al, Fe, Ca and Na and are homogeneous within a mineral grains and a xenolith. Garnets from Jagersfontein are chemically zoned for Cr, Ca, Ti and water contents. Garnets contain 0 to 20 ppm H2 Despite the fast diffusion rate of H in mantle m inerals, the observations above indicate that the water contents of mantle xenolith minerals were not disturbed during kimberlite entrainment and that the measured water data represent mantle values. Trace elements in all minerals show various degrees of light REE and LILE enrichments indicative of minimal to strong metasomatism. Water contents of peridotite minerals from the Kaapvaal lithosphere are not related to the degree of depletion of the peridotites. Instead, metasomatism exerts a clear control on the amount of water of mantle minerals. Xenoliths from each location record specific types of metasomatism with different outcomes for the water contents of mantle minerals. At pressures . 5.5 GPa, highly alkaline melts metasomatized Liqhobong and Kimberley peridotites, and increased the water contents of their olivine, pyroxenes and garnet. At higher pressures, the circulation of ultramafic melts reacting with peridotite resulted in co-variation of Ca, Ti and water at the edge of garnets at Jagersfontein, overall decreasing their water content, and lowered the water content of olivines at Finsch Mine. The calculated water content of these melts varies depending on whether the water content of the peridotite (2 wt% HO. 2O) or individual m inerals (<0.5-13 wt% H2O) are used, and also depend on the mineral-melt water partition coefficients. These metasomatic events are thought to have occurred during the Archean and Proterozoic, meaning that the water contents measured here have been preserved since that time and can be used to investigate viscocity and longevity of cratonic mantle roots.

Peslier, Anne H.↗
DOE OSTI2022

Role of Eu-Doping in the Electron Transport Behavior in the Zintl Thermoelectric Ca 5-x-y Yb x Eu y Al 2 Sb 6 System

A series of Eu-doped Zintl compounds belonging to theCa 5-x-y Yb x Eu y Al 2 Sb 6 (x = 0, 1.12; 0 ≤ y ≤ 0.63(2)) system have been successfully synthesized by both the arc-melting and the molten Pb-flux methods. All of the five title compounds initially crystallized in the Ca 5 Ga 2 As 6 -type phase (space group Pbam, Z = 2, Pearson code oP26) and maintained their original structure even after the post-heat treatment, unlike the recently reported n-type Zintl analogues in the Ca 5-x-y Yb x RE y Al 2 Sb 6 (RE = Pr, Nd, Sm) systems, which underwent a phase transition from the Ca 5 Ga 2 As 6 -type to the Ca 5 Al 2 Bi 6 -type phase after annealing. This research aimed to understand the origin of the structural preference of the title Ca 5-x-y Yb x Eu y Al 2 Sb 6 system, whether it was affected by the valence electron count or the cationic size. Electrical transport property measurements showed an increase in electrical conductivities and a decrease of Seebeck coefficients for Ca 4.89(1) Eu 0.11 Al 2 Sb 6 , Ca 4.82(1) Eu 0.18 Al 2 Sb 6 , and Ca 4.62(1) Eu 0.38 Al 2 Sb 6 , compared to the parental compound Ca 5 Al 2 Sb 6 . Hole effect measurements proved that these changes should be attributed to the reduced carrier concentration and enhanced carrier mobility. The comprehensive density functional theory calculations including electron density map analysis for the hypothetical model Ca 4.5 Eu 0.5 Al 2 Sb 6 revealed that the polarity between Al and Sb forming the anionic frameworks decreased as the Eu-dopants were introduced, which eventually affected the carrier mobility in the anionic frameworks. Thermal conductivity measurements proved that the Eu-doping successfully lowered the lattice thermal conductivity because of the enhanced atomic disordering. In conclusion, the magnetization measurements for Ca 4.37(2) Eu 0.63 Al 2 Sb 6 showed a typical Curie–Weiss behavior with weak antiferromagnetic nearest-neighbor interactions with θ p = -5.07 K.

36 MATERIALS SCIENCE↗