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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Understanding CO 2 adsorption on the surfaces of SrO and its hydroxylated variants Sr(OH) 2 · n H 2 O ( n = 0, 1, 8)

Strontium oxide (SrO) is a promising material for CO 2 capture through a reversible cycle of carbonation and calcination, where SrO reacts with CO 2 to form SrCO 3 and can be regenerated by calcination. In the presence of moisture, SrO forms strontium hydroxide and its hydrates (Sr(OH) 2 ·nH 2 O). Here, this study, which employs density functional theory, investigates the CO 2 adsorption mechanism of these processes on various crystal surfaces, including SrO, Sr(OH) 2 , Sr(OH) 2 ·1H 2 O, and Sr(OH) 2 ·8H 2 O. A significant finding is that the interaction of CO 2 with these surfaces leads to carbonate/bicarbonate formation via electron transfer, with notable differences in CO 2 orientation and bond characteristics between SrO surfaces and its hydroxylated surfaces. To explore the effects of moisture on CO 2 adsorption, H 2 O adsorption on these stable surfaces was investigated. The results showed that H 2 O reacts with the SrO (100) surface to form hydroxyl (OH) groups while it bonds with the surfaces of Sr(OH) 2 ·nH 2 O (n = 0, 1, 8) with hydrogen bonding. A small amount of H 2 O can enhance CO2 adsorption while a large amount of H 2 O could decrease the capability of CO 2 adsorption.

CO2 capture↗
DOE OSTI2020

Defect accommodation in off-stoichiometric (SrTiO 3 ) n SrO Ruddlesden–Popper superlattices studied with positron annihilation spectroscopy

he low dielectric loss underlying the record performance of strained (SrTiO 3 ) n SrO Ruddlesden–Popper films as tunable microwave dielectrics was postulated to arise from (SrO) 2 faults accommodating local non-stoichiometric defects. Here, we explore the effect of non-stoichiometry on (SrTiO 3 ) n SrO using positron annihilation lifetime spectroscopy on a composition series of 300 nm thick n = 6 (Sr 1+δ TiO 3 ) n SrO thin films. These films show titanium-site vacancies across the stoichiometry series, with evidence that TiO x vacancy complexes dominate. Little change in defect populations is observed across the series, indicating the ability of Ruddlesden–Popper phases to accommodate ± 5% off-stoichiometry. This ability for defect accommodation is corroborated by scanning transmission electron microscopy with electron energy loss spectroscopy.

Physics↗
DOE OSTI2019

Influence of crystalline order and defects on the absolute work functions and electron affinities of TiO2- and SrO-terminated n-SrTiO3(001)

We establish how the detailed structure and composition of the terminal layer of n-SrTiO3 (001) determine key surface electronic properties. We have measured and calculated from first principles the absolute work functions and electron affinities of bulk SrNb0.01Ti0.99O3(001) with both TiO2 and nominally SrO terminal planes. The match between theory and experiment is excellent at 4.6(1) eV for the TiO2 termination if an ideal, bulk-truncated surface structure is assumed. In contrast, the ideal SrO-termination leads to a calculated work function that is ~1.3 eV lower than the experimental value of 3.6(1) eV. We show that this discrepancy is associated with defects on the SrO surface that serve as electron scavengers. These defects deplete the concentration of itinerant electrons in the subsurface region and increase the negative charge density on the surface, thus increasing the work function. Several different surface defect configurations were modeled; the ones that yield the best agreement with experiment involve Sr vacancies in the terminal layer along with OH–/H– pairs or O22– occupying anion sites adjacent to the Sr vacancies.

Chambers, Scott A.↗
DOE OSTI2021

Ce stabilized Ni–SrO as a catalytic phase transition sorbent for integrated CO 2 capture and CH 4 reforming

Integration of carbon dioxide capture from flue gas with dry reforming of CH 4 represents an attractive approach for CO 2 utilization. The selection of a suitable bifunctional material serving as a catalyst/sorbent is the key. This paper reports Ni decorated and CeO x -stabilized SrO (SrCe 0.5 Ni 0.5 ) as a multi-functional, phase transition catalytic sorbent material. The effect of CeO x on the morphology, structure, decarbonation reactivity, and cycling stability of the catalytic sorbent was determined with TEM-EDX, XRD, in situ XRD, CH 4 -TPR and TGA. Here, cyclic process tests were conducted in a packed bed reactor. The results indicate that large Ni clusters were present on the surface of the SrNi sorbent, and the addition of CeO 2 promoted even distribution of Ni on the surface. Moreover, the Ce–Sr interaction promoted a complex carbonation/decarbonation phase-transition, i.e. SrCO 3 + CeO 2 ↔ Sr 2 CeO 4 + CO 2 as opposed to the conventional, simple carbonation/decarbonation cycles (e.g. SrCO 3 ↔ SrO + CO 2 ). This double replacement crystalline phase transition mechanism not only adjusts the carbonation/calcination thermodynamics to facilitate SrCO 3 decomposition at relatively low temperatures but also inhibits sorbent sintering. As a result, excellent activity and stability were observed with up to 91% CH 4 conversion, >72% CO 2 capture efficiency and ~100% residual O 2 capture efficiency from flue gas by utilizing the CeO 2 ↔ Ce 2 O 3 redox transition. This renders an intensified process with zero coke deposition. Moreover, the SLDRM with SrCe 0.5 Ni 0.5 has the flexibility to produce concentrated CO via CO 2 -splitting while co-producing a syngas with tunable H 2 /CO ratios.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Theoretical study of CO2 capture mechanisms of SrO and Sr(OH)2.nH2O (n=0,1,8)

This presentation encapsulated the use of density functional theory (DFT) to investigate the mechanism of CO2 conversion on various crystal surfaces, including SrO, Sr(OH)2, Sr(OH)2·H2O, and Sr(OH)2·8H2O. The study provides unique insights into the fundamental mechanism for CO2 capture using SrO and its hydrated forms.

catalyst performance↗
DOE OSTI2020

Materials Data on SrO by Materials Project

SrO is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Sr2+ is bonded to six equivalent O2- atoms to form a mixture of edge and corner-sharing SrO6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Sr–O bond lengths are 2.60 Å. O2- is bonded to six equivalent Sr2+ atoms to form a mixture of edge and corner-sharing OSr6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SrO by Materials Project

SrO is Molybdenum Carbide MAX Phase-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Sr2+ is bonded to six equivalent O2- atoms to form a mixture of distorted edge and corner-sharing SrO6 pentagonal pyramids. All Sr–O bond lengths are 2.60 Å. O2- is bonded to six equivalent Sr2+ atoms to form a mixture of edge, corner, and face-sharing OSr6 octahedra. The corner-sharing octahedral tilt angles are 47°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SrO by Materials Project

SrO crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Sr2+ is bonded to five equivalent O2- atoms to form a mixture of corner and edge-sharing SrO5 trigonal bipyramids. There are a spread of Sr–O bond distances ranging from 2.49–2.62 Å. O2- is bonded to five equivalent Sr2+ atoms to form a mixture of corner and edge-sharing OSr5 trigonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SrO by Materials Project

SrO is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Sr2+ is bonded in a body-centered cubic geometry to eight equivalent O2- atoms. All Sr–O bond lengths are 2.72 Å. O2- is bonded in a body-centered cubic geometry to eight equivalent Sr2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Thermal conductivity of the n = –5 and 10 members of the (SrTiO 3 ) n SrO Ruddlesden–Popper superlattices

Unlike many superlattice structures, Ruddlesden–Popper phases have atomically abrupt interfaces useful for interrogating how periodic atomic layers affect thermal properties. Here, we measure the thermal conductivity in thin films of the n = 1–5 and 10 members of the (SrTiO 3 ) n SrO Ruddlesden–Popper superlattices grown by molecular-beam epitaxy and compare the results to a single crystal of the n = 1 Ruddlesden–Popper SrLaAlO 4 . The thermal conductivity cross-plane to the superlattice layering (k 33 ) is measured using time-domain thermoreflectance as a function of temperature and the results are compared to first-principles calculations. The thermal conductivity of this homologous series decreases with increasing interface density. Characterization by x-ray diffraction and scanning transmission electron microscopy confirms that these samples have a Ruddlesden–Popper superlattice structure.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Theoretical study of CO2 capture mechanisms of SrO and Sr(OH)2.nH2O (n=0,1,8)

<span style="font-family: Roboto; font-size: 11pt;">In this presentation, the adsorption reactions of CO</span><sub style="font-family: Roboto; font-size: 11pt;">2</sub><span style="font-family: Roboto; font-size: 11pt;"> on SrO surfaces and its hydrated counterparts are examined. The predicted energies of CO</span><sub style="font-family: Roboto; font-size: 11pt;">2</sub><span style="font-family: Roboto; font-size: 11pt;"> adsorption on follows the order of increasing H</span><sub style="font-family: Roboto; font-size: 11pt;">2</sub><span style="font-family: Roboto; font-size: 11pt;">O content. The carbonation on the monohydrate surface is barrierless, whereas the CO</span><sub style="font-family: Roboto; font-size: 11pt;">2</sub><span style="font-family: Roboto; font-size: 11pt;"> reaction on the Sr(OH)</span><sub style="font-family: Roboto; font-size: 11pt;">2</sub><span style="font-family: Roboto; font-size: 11pt;"> and the octahydrate surfaces follows pathways with finite activation barriers. The thermodynamics of bulk reaction is also addressed.</span>

computational science and engineering↗
NASA NTRS1972

Diffusion in the system K2O-SrO-SiO2. II - Cation self-diffusion coefficients.

The self-diffusion coefficients were measured by introducing a slab of glass previously irradiated in a reactor between two slabs of unirradiated glass. By heating the specimens, etching them sequentially and determining the radioactivity, self-diffusion coefficients for K and Sr were measured. It is pointed out that the results obtained in the investigations appear to support the proposal that the network of the base glass predominantly controls the activation energy for the diffusion of ions.

Varshneya, A. K.↗