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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

CO 2 Hydrogenation to Methanol over Inverse ZrO 2 /Cu(111) Catalysts: The Fate of Methoxy under Dry and Wet Conditions

Understanding the surface chemistry of CH 3 O species is essential for the production of methanol by CO 2 hydrogenation over Cu-based heterogeneous catalysts, as it facilitates the rational design of more efficient conversion processes. Recent research has identified inverse ZrO 2 /Cu catalysts as highly active and selective systems for the transformation of CO 2 to methanol with a performance that can be better than that of commercial Cu/ZnO catalysts. Here, we employed synchrotron-based ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and calculations based on density functional theory (DFT) to understand the fate of CH 3 O groups under dry and wet environments. AP-XPS spectra revealed that under CO 2 hydrogenation conditions, formate and methoxy are two key intermediates to produce methanol. Furthermore, there are three different types of reactive sites on the surface: One is active for methoxy adsorption, which is stable and responsible for the methanol synthesis; Another one transforms CO 2 into CO; and a third one is active for CO 2 and methoxy dissociation, leading to C and methane formation. The theoretical calculations indicate that CH 3 OH readily dissociates to CH 3 O species following a highly exothermic (ΔE = -20.99 kcal/mol) and barrierless process. The water produced by the reverse water-gas shift reaction (CO 2 + H 2 → H 2 O + CO) can prevent the decomposition of CH 3 O species. We discovered that by introducing a tiny amount of water vapor (2 × 10 -6 Torr) into the reaction chamber, the energy barrier for the reaction CH 3 O(ads) + H(ads) → CH 3 OH(gas) is dramatically reduced. AP-XPS and computational modelling showed that water is quite capable of extracting adsorbed methoxy to form gaseous methanol. With this in mind, one could boost the methanol selectivity by adding appropriate amounts of water or steam, which is an inexpensive and feasible solution for industrial operations.

36 MATERIALS SCIENCE↗
NASA NTRS1987

Autogenic-feedback training: A preventive method for space adaptation syndrome

The progress made to date on the reduction of data for Spacelab 3 Shuttle experiment, No. 3AFT23 is reported. Four astronauts participated as subjects in this experiment. Crewmen A and B served as treatment subjects (i.e., received preflight training for control of their own motion sickness symptoms) and Crewmen C and D served as control (i.e., did not receive training). A preliminary evaluation of Autogenic Feedback Training (AFT) was made from visual inspections of graphs that were generated from the preflight and inflight and inflight physiological data which included: (1) Baseline rotating chair tests for all crewmen; (2) Posttraining rotating chair tests of treatment groups subjects; (3) Preflight data from Joint Integrated Simulations for all crewmen; and (4) Flight data for all crewmen during mission days 0 through 4, and mission day 6 for treatment subjects only. A summary of the findings suggested by these data is outlined.

Cowings, Patricia S.↗
DOE OSTI2020

Materials Data on K3Sb7(SO3)3 by Materials Project

K3Sb7(SO3)3 crystallizes in the hexagonal P6_3 space group. The structure is three-dimensional. K1+ is bonded to one S2- and six O2- atoms to form distorted corner-sharing KSO6 hexagonal pyramids. The K–S bond length is 3.22 Å. There are a spread of K–O bond distances ranging from 2.78–3.02 Å. There are three inequivalent Sb3+ sites. In the first Sb3+ site, Sb3+ is bonded in a distorted T-shaped geometry to three O2- atoms. There are two shorter (2.00 Å) and one longer (2.03 Å) Sb–O bond lengths. In the second Sb3+ site, Sb3+ is bonded in a 3-coordinate geometry to three O2- atoms. There are a spread of Sb–O bond distances ranging from 2.01–2.05 Å. In the third Sb3+ site, Sb3+ is bonded in a trigonal non-coplanar geometry to three equivalent S2- atoms. All Sb–S bond lengths are 2.45 Å. S2- is bonded in a 2-coordinate geometry to one K1+ and one Sb3+ atom. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent K1+ and two Sb3+ atoms. In the second O2- site, O2- is bonded to two equivalent K1+ and two Sb3+ atoms to form a mixture of distorted corner and edge-sharing OK2Sb2 tetrahedra. In the third O2- site, O2- is bonded to two equivalent K1+ and two Sb3+ atoms to form a mixture of distorted corner and edge-sharing OK2Sb2 tetrahedra.

36 MATERIALS SCIENCE↗
NASA NTRS2016

Individual Variability in Aerobic Fitness Adaptations to 70-d of Bed Rest and Exercise Training

Change in maximal aerobic capacity (VO2pk) in response to exercise training and disuse is highly variable among individuals. Factors that could contribute to the observed variability (lean mass, daily activity, diet, sleep, stress) are not routinely controlled in studies. The NASA bed rest (BR) studies use a highly controlled hospital based model as an analog of spaceflight. In this study, diet, hydration, physical activity and light/dark cycles were precisely controlled and provided the opportunity to investigate individual variability. PURPOSE. Evaluate the contribution of exercise intensity and lean mass on change in VO2pk during 70-d of BR or BR + exercise. METHODS. Subjects completed 70-d of BR alone (CON, N=9) or BR + exercise (EX, N=17). The exercise prescription included 6 d/wk of aerobic exercise at 70 - 100% of max and 3 d/wk of lower body resistance exercise. Subjects were monitored 24 hr/d. VO2pk and lean mass (iDXA) were measured pre and post BR. ANOVA was used to evaluate changes in VO2pk pre to post BR. Subjects were retrospectively divided into high and low responders based on change in VO2pk (CON > 20% loss, n=5; EX >10% loss, n=4, or 5% gain, n=4) to further understand individual variability. RESULTS. VO2pk decreased from pre to post BR in CON (P<0.05) and was maintained in EX; however, significant individual variability was observed (CON: -22%, range: -39% to -.5%; EX: -1.8%, range: -16% to 12.6%). The overlap in ranges between groups included 3 CON who experienced smaller reduction in VO2pk (<16%) than the worst responding EX subjects. Individual variability was maintained when VO2pk was normalized to lean mass (range, CON: -33.7% to -5.7%; EX: -15.8% to 11%), and the overlap included 5 CON with smaller reductions in VO2pk than the worst responding EX subjects. High responders to disuse also lost the most lean mass; however, this relationship was not maintained in EX (i.e. the largest gains/losses in lean mass were observed in both high and low responders). Change in VO2pk was not related to exercise intensity. CONCLUSION. Change in VO2pk in response to disuse and exercise was highly variable among individuals, even in this tightly controlled study. Loss in lean mass accounts for a significant degree of variability in the CON; however, training induced gains in VO2pk appear unrelated to lean mass or exercise intensity.

Downs, Meghan↗
DOE OSTI2020

Materials Data on Y(HO)3 by Materials Project

Y(OH)3 crystallizes in the hexagonal P6_3 space group. The structure is three-dimensional. Y3+ is bonded in a 9-coordinate geometry to nine equivalent O2- atoms. There are a spread of Y–O bond distances ranging from 2.41–2.50 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 single-bond geometry to three equivalent Y3+ and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on La(HO)3 by Materials Project

La(OH)3 crystallizes in the hexagonal P6_3 space group. The structure is three-dimensional. La3+ is bonded in a 9-coordinate geometry to nine equivalent O2- atoms. There are a spread of La–O bond distances ranging from 2.53–2.68 Å. H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. O2- is bonded in a single-bond geometry to three equivalent La3+ and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2026

SMEFT ATLAS: The landscape beyond the Standard Model

The Standard Model Effective Field Theory (SMEFT) based on the unbroken gauge group SU(3) 𝐶 ⊗SU(2) 𝐿 ⊗U(1) 𝑌 and containing only particles of the Standard Model (SM) has developed in the last decade to a mature field. It is the framework to be used in the energy gap from scales sufficiently higher than the electroweak scale up to the lowest energy scale at which new particles show up. We summarize the present status of this theory with a particular emphasize on its role in the indirect search for new physics (NP). While flavour physics of both quarks and leptons is the main topic of our review, we also discuss electric dipole moments, anomalous magnetic moments (𝑔−2) 𝜇,𝑒 , 𝑍-pole observables, Higgs observables and high-𝑝𝑇 scattering processes within the SMEFT. We group the observables into ten classes and list for each class the most relevant operators and the corresponding renormalization group equations (RGEs). We exhibit the correlations between different classes implied both by the operator mixing and the SU(2) 𝐿 gauge symmetry. Our main goal is to provide an insight into the complicated operator structure of this framework which hopefully will facilitate the identification of valid ultraviolet completions behind possible anomalies observed in future data. Numerous colourful charts, and 85 tables, while representing rather complicated RG evolution from the NP scale down to the electroweak scale, beautify the involved SMEFT landscape. Over 1000 references to the literature underline the importance and the popularity of this field. We discuss both top-down and bottom-up approaches as well as their interplay. This allows us eventually to present an atlas of different landscapes beyond the SM that includes heavy gauge bosons and scalars, vector-like quarks and leptons and leptoquarks.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Materials Data on Al(IO3)3 by Materials Project

Al(IO3)3 crystallizes in the hexagonal P6_3 space group. The structure is three-dimensional. Al3+ is bonded in an octahedral geometry to six O2- atoms. There is three shorter (1.92 Å) and three longer (1.93 Å) Al–O bond length. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to one Al3+ and one I5+ atom. The O–I bond length is 1.88 Å. In the second O2- site, O2- is bonded in a bent 120 degrees geometry to one Al3+ and one I5+ atom. The O–I bond length is 1.85 Å. In the third O2- site, O2- is bonded in a distorted single-bond geometry to one I5+ atom. The O–I bond length is 1.80 Å. I5+ is bonded in a 3-coordinate geometry to three O2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on In(IO3)3 by Materials Project

In(IO3)3 crystallizes in the hexagonal P6_3 space group. The structure is three-dimensional. In3+ is bonded in an octahedral geometry to six O2- atoms. There are three shorter (2.18 Å) and three longer (2.19 Å) In–O bond lengths. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to one I5+ atom. The O–I bond length is 1.80 Å. In the second O2- site, O2- is bonded in a bent 120 degrees geometry to one In3+ and one I5+ atom. The O–I bond length is 1.86 Å. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one In3+ and one I5+ atom. The O–I bond length is 1.87 Å. I5+ is bonded in a 3-coordinate geometry to three O2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ga(IO3)3 by Materials Project

Ga(IO3)3 crystallizes in the hexagonal P6_3 space group. The structure is three-dimensional. Ga3+ is bonded in an octahedral geometry to six O2- atoms. There are three shorter (2.00 Å) and three longer (2.01 Å) Ga–O bond lengths. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to one I5+ atom. The O–I bond length is 1.80 Å. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ga3+ and one I5+ atom. The O–I bond length is 1.89 Å. In the third O2- site, O2- is bonded in a bent 120 degrees geometry to one Ga3+ and one I5+ atom. The O–I bond length is 1.86 Å. I5+ is bonded in a 3-coordinate geometry to three O2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Confinement of quasi-atomic structures in Ti 2 N and Ti 3 N 2 MXene electrides

Metal carbides, nitrides, or carbonitrides of early transition metals, better known as MXenes, possess notable structural, electrical, and magnetic properties. Analyzing electronic structures by calculating structural stability, band structure, density of states, Bader charge transfer, and work functions utilizing first principle calculations, we revealed that titanium nitride MXenes, namely Ti 2 N and Ti 3 N 2 , have excess anionic electrons in their lattice voids, making them MXene electrides. Bulk Ti 3 N 2 has competing antiferromagnetic (AFM) and ferromagnetic (FM) configurations with slightly more stable AFM configuration, while the Ti 2 N MXene is nonmagnetic. Although Ti 3 N 2 favors AFM configuration with hexagonal crystal systems having 6/ mmm point group symmetry, Ti 3 N 2 does not support altermagnetism. The monolayer of the Ti 3 N 2 MXene is a ferromagnetic electride. These unique properties of having non-nuclear interstitial anionic electrons in the electronic structure of titanium nitride MXene have not yet been reported in the literature. Density functional theory calculations show TiN is neither an electride, MXene, or magnetic.

Anionic electrons↗
DOE OSTI2020

Materials Data on Ca5As3HO13 by Materials Project

Ca5(AsO4)3OH crystallizes in the hexagonal P6_3 space group. The structure is three-dimensional. there are three inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are three shorter (2.40 Å) and three longer (2.49 Å) Ca–O bond lengths. In the second Ca2+ site, Ca2+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of Ca–O bond distances ranging from 2.41–2.93 Å. In the third Ca2+ site, Ca2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ca–O bond distances ranging from 2.35–2.50 Å. As5+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of As–O bond distances ranging from 1.71–1.73 Å. H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ca2+ and one As5+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to three equivalent Ca2+ and one H1+ atom. In the third O2- site, O2- is bonded to three Ca2+ and one As5+ atom to form distorted edge-sharing OCa3As tetrahedra. In the fourth O2- site, O2- is bonded in a 1-coordinate geometry to two Ca2+ and one As5+ atom. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to three Ca2+ and one As5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiMn4(PO4)3 by Materials Project

LiMn4(PO4)3 crystallizes in the hexagonal P6_3 space group. The structure is three-dimensional. Li1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are three shorter (2.17 Å) and three longer (2.46 Å) Li–O bond lengths. There are two inequivalent Mn2+ sites. In the first Mn2+ site, Mn2+ is bonded to five O2- atoms to form distorted MnO5 trigonal bipyramids that share corners with three equivalent PO4 tetrahedra, corners with four equivalent MnO5 trigonal bipyramids, and an edgeedge with one PO4 tetrahedra. There are a spread of Mn–O bond distances ranging from 2.08–2.35 Å. In the second Mn2+ site, Mn2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are three shorter (2.22 Å) and three longer (2.29 Å) Mn–O bond lengths. P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with three equivalent MnO5 trigonal bipyramids and an edgeedge with one MnO5 trigonal bipyramid. There are a spread of P–O bond distances ranging from 1.53–1.57 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Mn2+ and one P5+ atom. In the second O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Mn2+ and one P5+ atom. In the third O2- site, O2- is bonded to one Li1+, two Mn2+, and one P5+ atom to form distorted edge-sharing OLiMn2P tetrahedra. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Li1+, one Mn2+, and one P5+ atom.

36 MATERIALS SCIENCE↗
NASA NTRS2011

Comparisons of Mineralogy Between Cumulate Eucrites and Lunar Meteorites Possibly from the Farside Anorsothitic Crust

Anorthosites composed of nearly pure anorthite (PAN) at many locations in the farside highlands have been observed by the Kaguya multiband imager and spectral profiler [1]. Mineralogical studies of lunar meteorites of the Dhofar 489 group [2,3] and Yamato (Y-) 86032 [4], all possibly from the farside highlands, showed some aspects of the farside crust. Nyquist et al. [5] performed Sm-Nd and Ar-Ar studies of pristine ferroan anorthosites (FANs) of the returned Apollo samples and of Dhofar 908 and 489, and discussed implications for lunar crustal history. Nyquist et al. [6] reported initial results of a combined mineralogical/chronological study of the Yamato (Y-) 980318 cumulate eucrite with a conventional Sm-Nd age of 4567 24 Ma and suggested that all eucrites, including cumulate eucrites, crystallized from parental magmas within a short interval following differentiation of their parent body, and most eucrites participated in an event or events in the time interval ~4400- 4560 Ma in which many isotopic systems were partially reset. During the foregoing studies, we recognized that variations in mineralogy and chronology of lunar anorthosites are more complex than those of the crustal materials of the HED parent body. In this study, we compared the mineralogies and reflectance spectra of the cumulate eucrites, Y-980433 and 980318, to those of the Dhofar 307 lunar meteorite of the Dhofar 489 group [2]. Here we consider information from these samples to gain a better understanding of the feldspathic farside highlands and the Vesta-like body.

Takeda, H.↗
DOE OSTI2020

Materials Data on Ca5As3ClO12 by Materials Project

Ca5(AsO4)3Cl crystallizes in the hexagonal P6_3 space group. The structure is three-dimensional. there are three inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are three shorter (2.41 Å) and three longer (2.48 Å) Ca–O bond lengths. In the second Ca2+ site, Ca2+ is bonded in a 6-coordinate geometry to nine O2- atoms. There are a spread of Ca–O bond distances ranging from 2.41–2.96 Å. In the third Ca2+ site, Ca2+ is bonded to five O2- and one Cl1- atom to form distorted CaClO5 pentagonal pyramids that share corners with six equivalent CaClO5 pentagonal pyramids, corners with three equivalent AsO4 tetrahedra, and an edgeedge with one AsO4 tetrahedra. There are a spread of Ca–O bond distances ranging from 2.34–2.55 Å. The Ca–Cl bond length is 2.80 Å. As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with three equivalent CaClO5 pentagonal pyramids and an edgeedge with one CaClO5 pentagonal pyramid. There are a spread of As–O bond distances ranging from 1.71–1.75 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ca2+ and one As5+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to two Ca2+ and one As5+ atom. In the third O2- site, O2- is bonded to three Ca2+ and one As5+ atom to form distorted edge-sharing OCa3As tetrahedra. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to three Ca2+ and one As5+ atom. Cl1- is bonded in a trigonal non-coplanar geometry to three equivalent Ca2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiSiBiO4 by Materials Project

LiSiBiO4 crystallizes in the hexagonal P6_3 space group. The structure is three-dimensional. Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with two equivalent BiO6 octahedra and corners with four equivalent SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 59–78°. There are a spread of Li–O bond distances ranging from 1.88–2.08 Å. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two equivalent BiO6 octahedra and corners with four equivalent LiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 50–56°. There is three shorter (1.65 Å) and one longer (1.67 Å) Si–O bond length. There are three inequivalent Bi3+ sites. In the first Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are three shorter (2.34 Å) and three longer (2.49 Å) Bi–O bond lengths. In the second Bi3+ site, Bi3+ is bonded to six O2- atoms to form distorted BiO6 octahedra that share corners with six equivalent LiO4 tetrahedra and corners with six equivalent SiO4 tetrahedra. There are three shorter (2.27 Å) and three longer (2.64 Å) Bi–O bond lengths. In the third Bi3+ site, Bi3+ is bonded in a 3-coordinate geometry to three equivalent O2- atoms. All Bi–O bond lengths are 2.19 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one Li1+, one Si4+, and one Bi3+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one Li1+, one Si4+, and one Bi3+ atom. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Li1+, one Si4+, and two Bi3+ atoms. In the fourth O2- site, O2- is bonded in a trigonal planar geometry to one Li1+, one Si4+, and one Bi3+ atom.

36 MATERIALS SCIENCE↗
NASA NTRS2001

Autogenic Feedback Training Exercise and pilot performance: enhanced functioning under search-and-rescue flying conditions

Studies have shown that autonomous mode behavior is one cause of aircraft fatalities due to pilot error. In such cases, the pilot is in a high state of psychological and physiological arousal and tends to focus on one problem, while ignoring more critical information. This study examined the effect of training in physiological self-recognition and regulation, as a means of improving crew cockpit performance. Seventeen pilots were assigned to the treatment and control groups matched for accumulated flight hours. The treatment group contained 4 pilots from HC-130 Hercules aircraft and 4 HH-65 Dolphin helicopter pilots; the control group contained 3 pilots of HC-130s and 6 helicopter pilots. During an initial flight, physiological data were recorded on each crewmember and an instructor pilot rated individual crew performance. Eight crewmembers were then taught to regulate their own physiological response levels using Autogenic-Feedback Training Exercise (AFTE). The remaining participants received no training. During a second flight, treatment participants showed significant improvement in performance (rated by the same instructor pilot as in pretests) while controls did not improve. The results indicate that AFTE management of high states of physiological arousal may improve pilot performance during emergency flying conditions.

NASA Discipline Neuroscience↗
DOE OSTI2020

Materials Data on As3Pb5ClO9 by Materials Project

Pb5As3O9Cl crystallizes in the hexagonal P6_3 space group. The structure is three-dimensional. there are three inequivalent Pb2+ sites. In the first Pb2+ site, Pb2+ is bonded in a 4-coordinate geometry to three O2- and one Cl1- atom. There are two shorter (2.30 Å) and one longer (2.64 Å) Pb–O bond lengths. The Pb–Cl bond length is 3.04 Å. In the second Pb2+ site, Pb2+ is bonded in a 7-coordinate geometry to six O2- and one Cl1- atom. There are three shorter (2.67 Å) and three longer (2.76 Å) Pb–O bond lengths. The Pb–Cl bond length is 2.92 Å. In the third Pb2+ site, Pb2+ is bonded to six equivalent O2- atoms to form distorted face-sharing PbO6 octahedra. There are three shorter (2.43 Å) and three longer (2.91 Å) Pb–O bond lengths. As3+ is bonded in a trigonal non-coplanar geometry to three O2- atoms. There are a spread of As–O bond distances ranging from 1.79–1.83 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to three Pb2+ and one As3+ atom. In the second O2- site, O2- is bonded in a 1-coordinate geometry to two Pb2+ and one As3+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to two Pb2+ and one As3+ atom. Cl1- is bonded in a trigonal pyramidal geometry to four Pb2+ atoms.

36 MATERIALS SCIENCE↗