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6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Tunable Ferromagnetism in LaCoO 3 Epitaxial Thin Films

We report ferromagnetic insulators play a crucial role in the development of low-dissipation quantum magnetic devices for spintronics. Epitaxial LaCoO 3 thin film is a prominent ferromagnetic insulator, in which the robust ferromagnetic ordering emerges owing to epitaxial strain. Whereas it is evident that strong spin-lattice coupling induces ferromagnetism, the reported ferromagnetic properties of epitaxially strained LaCoO 3 thin films are highly consistent. For example, even under largely modulated degree of strain, the reported Curie temperatures of epitaxially strained LaCoO 3 thin films lie in a narrow range of 80–85 K, without much deviation. In this study, substantial enhancement (≈18%) in the Curie temperature of epitaxial LaCoO 3 thin films is demonstrated via crystallographic orientation dependence. By changing the crystallographic orientation of the films from (111) to (110), the crystal-field energy is reduced and the charge transfer between the Co and O orbitals is enhanced. These modifications lead to a considerable enhancement of the ferromagnetic properties (including the Curie temperature and magnetization), despite the identical nominal degree of epitaxial strain. The findings of this study provide insights into facile tunability of ferromagnetic properties via structural symmetry control in LaCoO 3 .

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaCoO3 by Materials Project

LaCoO3 is Orthorhombic Perovskite structured and crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are two inequivalent La3+ sites. In the first La3+ site, La3+ is bonded in a 12-coordinate geometry to nine O2- atoms. There are a spread of La–O bond distances ranging from 2.40–2.94 Å. In the second La3+ site, La3+ is bonded in a 12-coordinate geometry to nine O2- atoms. There are a spread of La–O bond distances ranging from 2.40–2.95 Å. There are four inequivalent Co3+ sites. In the first Co3+ site, Co3+ is bonded to six O2- atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedra tilt angles range from 18–23°. There are a spread of Co–O bond distances ranging from 1.90–2.01 Å. In the second Co3+ site, Co3+ is bonded to six O2- atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedra tilt angles range from 18–24°. There are a spread of Co–O bond distances ranging from 1.95–2.04 Å. In the third Co3+ site, Co3+ is bonded to six O2- atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedra tilt angles range from 19–24°. There are a spread of Co–O bond distances ranging from 1.93–1.98 Å. In the fourth Co3+ site, Co3+ is bonded to six O2- atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedra tilt angles range from 19–23°. There are a spread of Co–O bond distances ranging from 1.97–2.02 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to three La3+ and two Co3+ atoms. In the second O2- site, O2- is bonded in a 4-coordinate geometry to three La3+ and two Co3+ atoms. In the third O2- site, O2- is bonded in a 4-coordinate geometry to three La3+ and two Co3+ atoms. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to three La3+ and two Co3+ atoms. In the fifth O2- site, O2- is bonded in a 5-coordinate geometry to three La3+ and two Co3+ atoms. In the sixth O2- site, O2- is bonded in a 5-coordinate geometry to three La3+ and two Co3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaCoO3 by Materials Project

LaCoO3 is Orthorhombic Perovskite-like structured and crystallizes in the triclinic P-1 space group. The structure is three-dimensional. La3+ is bonded in a 3-coordinate geometry to nine O2- atoms. There are a spread of La–O bond distances ranging from 2.40–2.81 Å. There are two inequivalent Co3+ sites. In the first Co3+ site, Co3+ is bonded to six O2- atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedra tilt angles range from 21–24°. There is two shorter (1.88 Å) and four longer (2.04 Å) Co–O bond length. In the second Co3+ site, Co3+ is bonded to six O2- atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedra tilt angles range from 21–24°. There are a spread of Co–O bond distances ranging from 1.95–2.11 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 5-coordinate geometry to three equivalent La3+ and two Co3+ atoms. In the second O2- site, O2- is bonded in a 5-coordinate geometry to three equivalent La3+ and two Co3+ atoms. In the third O2- site, O2- is bonded in a 5-coordinate geometry to three equivalent La3+ and two Co3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaCoO3 by Materials Project

LaCoO3 is Orthorhombic Perovskite-like structured and crystallizes in the triclinic P-1 space group. The structure is three-dimensional. La3+ is bonded in a 3-coordinate geometry to nine O2- atoms. There are a spread of La–O bond distances ranging from 2.42–2.79 Å. There are two inequivalent Co3+ sites. In the first Co3+ site, Co3+ is bonded to six O2- atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedra tilt angles range from 20–21°. There is two shorter (1.93 Å) and four longer (1.94 Å) Co–O bond length. In the second Co3+ site, Co3+ is bonded to six O2- atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedra tilt angles range from 20–21°. There are two shorter (2.00 Å) and four longer (2.02 Å) Co–O bond lengths. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 5-coordinate geometry to three equivalent La3+ and two Co3+ atoms. In the second O2- site, O2- is bonded in a 5-coordinate geometry to three equivalent La3+ and two Co3+ atoms. In the third O2- site, O2- is bonded in a 5-coordinate geometry to three equivalent La3+ and two Co3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Electronic parameters in cobalt-based perovskite-type oxides as descriptors for chemocatalytic reactions

Perovskite-type transition metal (TM) oxides are effective catalysts in oxidation and decomposition reactions. Yet, the effect of compositional variation on catalytic efficacy is not well understood. The present analysis of electronic characteristics of B-site substituted LaCoO3 derivatives via in situ X-ray absorption spectroscopy (XAS) establishes correlations of electronic parameters with reaction rates: TM t2g and eg orbital occupancy yield volcano-type or non-linear correlations with NO oxidation, CO oxidation and N2O decomposition rates. Covalent O 2p-TM 3d interaction, in ultra-high vacuum, is a linear descriptor for reaction rates in NO oxidation and CO oxidation, and for N2O decomposition rates in O2 presence. Covalency crucially determines the ability of the catalytically active sites to interact with surface species during the kinetically relevant step of the reaction. The nature of the kinetically relevant step and of surface species involved lead to the vast effect of XAS measurement conditions on the validity of correlations.

Science & Technology - Other Topics↗
DOE OSTI2024

Investigations on the Origin of Topotactic Phase Transition of LaCoO 3 Thin Films with In Situ XRD and Ambient Pressure Hard X-ray Photoelectron Spectroscopy

With the applications of in situ X-ray diffraction (XRD), electrical I–V measurement, and ambient pressure hard X-ray photoelectron spectroscopy (AP-HAXPES), the characteristics of the topotactic phase transition of LaCoO 3 (LCO) thin films are examined. XRD measurements show clear evidence of structural phase transition (SPT) of the LCO thin films from the perovskite (PV) LaCoO 3 to the brownmillerite (BM) La 2 Co 2 O 5 phases through the intermediate La 3 Co 3 O 8 phase at a temperature of 350 °C under high-vacuum conditions, ~10 –5 mbar. The reverse SPT from BM to PV phases is also found under ambient pressure (>100 mbar) of air near 100 °C. Both observed SPTs in XRD are also identified in the electrical I–V measurements, i.e., the metallic PV phase to the insulating BM phase and vice versa. During the onset of SPTs, the bulk chemical and electronic states of LCO thin films are monitored with AP-HAXPES. The oxidation states in Co 2p spectra indicate that the oxygen vacancies are closely related to the SPT of LCO thin films. Also, the presence of enlarged band gap is observed as the SPT from PV to BM phases takes place, revealing the modified electronic properties of LCO due to the creation of oxygen vacancies. In conclusion, the analysis of valence band structures is further compared to the I–V measurements.

36 MATERIALS SCIENCE↗