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14 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on LaMnO3 by Materials Project

LaMnO3 is (Cubic) Perovskite structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. La3+ is bonded to twelve equivalent O2- atoms to form LaO12 cuboctahedra that share corners with twelve equivalent LaO12 cuboctahedra, faces with six equivalent LaO12 cuboctahedra, and faces with eight equivalent MnO6 octahedra. All La–O bond lengths are 2.79 Å. Mn3+ is bonded to six equivalent O2- atoms to form MnO6 octahedra that share corners with six equivalent MnO6 octahedra and faces with eight equivalent LaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All Mn–O bond lengths are 1.97 Å. O2- is bonded in a distorted linear geometry to four equivalent La3+ and two equivalent Mn3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaMnO3 by Materials Project

LaMnO3 crystallizes in the trigonal R-3c space group. The structure is three-dimensional. La3+ is bonded in a 3-coordinate geometry to nine equivalent O2- atoms. There are three shorter (2.41 Å) and six longer (2.81 Å) La–O bond lengths. Mn3+ is bonded to six equivalent O2- atoms to form corner-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles are 24°. All Mn–O bond lengths are 2.03 Å. O2- is bonded in a 5-coordinate geometry to three equivalent La3+ and two equivalent Mn3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaMnO3 by Materials Project

LaMnO3 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. La3+ is bonded to six O2- atoms to form distorted LaO6 octahedra that share edges with three equivalent LaO6 octahedra and edges with three equivalent MnO6 octahedra. There are a spread of La–O bond distances ranging from 2.21–2.66 Å. There are two inequivalent Mn3+ sites. In the first Mn3+ site, Mn3+ is bonded to six O2- atoms to form distorted MnO6 octahedra that share edges with six equivalent LaO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.97–2.43 Å. In the second Mn3+ site, Mn3+ is bonded in a square co-planar geometry to four O2- atoms. All Mn–O bond lengths are 1.95 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted see-saw-like geometry to two equivalent La3+ and two Mn3+ atoms. In the second O2- site, O2- is bonded in a distorted see-saw-like geometry to two equivalent La3+ and two Mn3+ atoms. In the third O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two equivalent La3+ and one Mn3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaMnO3 by Materials Project

LaMnO3 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. La3+ is bonded to six O2- atoms to form distorted LaO6 octahedra that share edges with three equivalent LaO6 octahedra and edges with three equivalent MnO6 octahedra. There are a spread of La–O bond distances ranging from 2.26–2.66 Å. There are two inequivalent Mn3+ sites. In the first Mn3+ site, Mn3+ is bonded to six O2- atoms to form MnO6 octahedra that share edges with six equivalent LaO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.96–2.23 Å. In the second Mn3+ site, Mn3+ is bonded in a square co-planar geometry to four O2- atoms. There is two shorter (1.95 Å) and two longer (1.97 Å) Mn–O bond length. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent La3+ and two Mn3+ atoms. In the second O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two equivalent La3+ and two Mn3+ atoms. In the third O2- site, O2- is bonded in a trigonal non-coplanar geometry to two equivalent La3+ and one Mn3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaMnO3 by Materials Project

LaMnO3 crystallizes in the orthorhombic Pbam space group. The structure is three-dimensional. there are two inequivalent La3+ sites. In the first La3+ site, La3+ is bonded in a distorted body-centered cubic geometry to eight O2- atoms. There are a spread of La–O bond distances ranging from 2.52–2.79 Å. In the second La3+ site, La3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of La–O bond distances ranging from 2.52–2.79 Å. There are two inequivalent Mn3+ sites. In the first Mn3+ site, Mn3+ is bonded to six O2- atoms to form corner-sharing MnO6 octahedra. The corner-sharing octahedra tilt angles range from 0–25°. There are a spread of Mn–O bond distances ranging from 1.99–2.03 Å. In the second Mn3+ site, Mn3+ is bonded to six O2- atoms to form corner-sharing MnO6 octahedra. The corner-sharing octahedra tilt angles range from 0–25°. There are a spread of Mn–O bond distances ranging from 1.99–2.03 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted linear geometry to four La3+ and two equivalent Mn3+ atoms. In the second O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent La3+ and two Mn3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Precipitation of dopants on acceptor-doped LaMnO3±δ revealed by defect chemistry from first principles

Perovskite oxides degrade at elevated temperatures while precipitating dopant-rich particles on the surface. A knowledge-based improvement of surface stability requires a fundamental and quantitative understanding of the dopant precipitation mechanism on these materials. We propose that dopant precipitation is a consequence of the variation of dopant solubility between calcination and operating conditions in solid oxide fuel cells (SOFCs) and electrolyzer cells (SOECs). To study dopant precipitation, we use 20% (D = Ca, Sr, Ba)-doped LaMnO3+δ (LDM20) as a model system. We employ a defect model taking input from density functional theory calculations. The defect model considers the equilibration of LDM20 with a reservoir consisting of dopant oxide (DO), peroxide (DO2), and O2 in the gas phase. The equilibrated non-stoichiometry of the A-site and B-site as a function of temperature, T, and oxygen partial pressure, p(O2), reveals three regimes for LDM20: A-site deficient (oxidizing conditions), A-site rich (atmospheric conditions), and near-stoichiometric (reducing conditions). Assuming an initial A/B non-stoichiometry, we compute the dopant precipitation boundaries in a p–T phase diagram. Our model predicts precipitation both under reducing (DO) and under highly oxidizing conditions (DO2). We found precipitation under anodic, SOEC conditions to be promoted by large dopant size, while under cathodic, SOFC conditions precipitation is promoted by initial A-site excess. The main driving forces for precipitation are oxygen uptake by the condensed phase under oxidizing conditions and oxygen release assisted by B-site vacancies under reducing conditions. Possible strategies for mitigating dopant precipitation under in electrolytic and fuel cell conditions are discussed.

Hess, Franziska (ORCID:000000024460643X)↗
DOE OSTI2023

Chromium Poisoning Mitigation Strategy in Strontium-Doped Lanthanum Manganite-Based Air Electrodes in Solid Oxide Fuel Cells

Abstract Chromium poisoning of the air electrode remains an obstacle to the long-term performance of solid oxide fuel cells (SOFCs). In Sr-doped LaMnO3 (LSM) air electrodes, the poisoning process results in two types of deposits, chromium oxide (Cr2O3), and Mn, Cr spinel (MnCr2O4). The former forms electrochemically and the latter forms via a chemical reaction. By applying a small anodic reverse bias, Cr2O3 deposits can be removed because their formation is electrochemical in nature. However, MnCr2O4 deposits remain because their formation is chemical, rather than electrochemical, in nature. In situ chemical decomposition of the Mn, Cr spinel was investigated as an alternate removal method as thermodynamics supports its decomposition into constituent oxides below ∼540 °C in pure oxygen. The spinel decomposition process was characterized using thermogravimetric and X-ray diffraction analyses. The experimentally determined rate of spinel decomposition was undetectable (very slow) with isolated MnCr2O4 powders. The addition of 10 mol% gadolinia doped ceria (GDC) and silver powders significantly increased the rate of decomposition. However, the rate is limited by the diffusion of oxygen through the decomposed oxide layer. Although one strategy may be the addition of GDC and silver to the LSM air electrode to enhance spinel decomposition, the more effective mitigation strategy would be to prevent the formation of MnCr2O4 spinel in the first place through the removal of the reactants: Cr2O3 via electrochemical cleaning and mobile Mn ions in the zirconia electrolyte by incorporating a diffusion barrier layer such as GDC between the air electrode and electrolyte.

Electrochemistry↗
DOE OSTI2021

Dry reforming of methane over Ni supported on LaMnO 3 thin films

Thin films of LaMnO 3 were deposited onto MgAl 2 O 4 by Atomic Layer Deposition (ALD) and studied as supports for Ni in the Dry Reforming of Methane (DRM). Scanning Transmission Electron Microscopy (STEM) with Energy-Dispersive X-ray Spectroscopy (EDS) demonstrated that LaMnO 3 covered the support uniformly, and X-ray diffraction (XRD) showed that the LaMnO 3 films maintained their perovskite structure after 5 redox cycles at 1073 K. The Ni also remained well dispersed after 5 redox cycles at 1073 K. The LaMnO 3 -supported catalyst was more active than Ni on the unmodified MgAl 2 O 4 and showed superior resistance against coke formation. Lastly, the results for Ni on the LaMnO 3 films are compared to previous results for Ni on LaFeO 3 , CaTiO 3 , SrTiO 3 , and BaTiO 3 films.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗