Lanthanum Cobalt Oxide Research Articles

Structural Phase Transition from Rhombohedral to Cubic in LaCoO3

Lanthanum cobalt oxide LaCoO3 has a rhombohedrally distorted perovskite structure with the crystal space group of R3c.1-3) Raccah and Goodenough have reported that the crystal space group varies with increasing temperature from R3c to R3 around K. In the high temperature phase, two kinds of inequivalent Co atoms order preferentially on alternate (111) Co 2) They have also reported a first order insulator-to-metal phase transition at 1210K accompanied with an abrupt drop of the rhombohedral angle from 60.4◦ to 60◦ keeping R3 symmetry through the transition. In addition, they reported an endothermic first order transition at 1210K, and higher order phase transitions at around 550 and 900K from the differential thermal analysis. A powder neutron diffraction study has revealed that LaCoO3 has R3c symmetry between 4.2 and 1248K, with possible exception at 668K. According to the study, the rhombohedral angle remains 60.3◦ even at 1248K. Their study does not support the first order phase transition at 1210K. In order to investigate the structural phase transition of LaCoO3, we performed X-ray powder diffraction measurement, and thermogravimetric (TG) and differential thermal analysis (DTA) at high temperatures. The results suggest a second order crystallographic phase transition from rhombohedral to cubic around 1610K, and show that any anomaly previously reported is not intrinsic one in pure LaCoO3. The powder samples of LaCoO3 for X-ray diffraction measurements were obtained from single crystal grown with a lamp-image floating zone furnace. The X-ray powder diffraction measurements were performed using a high-accuracy X-ray powder diffractometer equipped with a parabolic multilayer and parallel slit analyzer between 300 and 1700K in air atmosphere. The thermogravimetric and differential thermal analysis (TG-DTA) was performed between 300 and 1773K for both single crystalline bulk and polycrystalline powder samples with a TG-DTA (Rigaku TG-8120D) coupled with a mass spectrometer (Q-MS, Rigaku Thermo-Mass QA550

Strontium-doped Lanthanum Cobalt Oxides Studied by XPS

La1−xSrxCoO3 is a perovskite-type magnetic material. LaCoO3 is a nonmagnetic semiconductor at low temperatures but it undergoes a gradual transition from the nonmagnetic ground state to a paramagnetic state above ∼90 K and then to a metal above ∼500 K. It has remained controversial whether the 90 K transition is a low spin-to-high spin transition or not. One aim of this research was to elucidate the origin of the magnetic transition and our conclusion was that it is not a low spin-to-high spin transition, but low spin-to-intermediate spin transition. By replacing La with Sr, the system changes from the nonmagnetic semiconductor to a ferromagnetic metal with increasing Sr concentration. This is similar to the colossal magnetoresistance (CMR) system La1−xSrxMnO3, and the system shows fairly large MR, in fact. However, in contrast to the manganese system, the present system shows only about a half of the full moment of the high spin Co ion. The other aim of this research was to understand the magnetic state of this system using photoemission spectroscopy. The samples were polycrystalline and were prepared by solid-state reaction. XPS measurements were carried out using Mg Kα source at liquid nitrogen temperature (∼80 K). In order to obtain a fresh clean surface, the samples were scraped with a diamond file in situ, and surface aging was monitored by observing the intensity of a tail at the higher binding-energy side of the O 1s peak. The surface typically lasted for 1–2 h.

Room temperature topotactic oxidation of lanthanum cobalt oxide La 2CoO 4.0

Lanthanum cobalt oxide La 2CoO 4 exhibits unusually fast oxygen transport in the spontaneous intercalation of molecular oxygen at ambient temperature. The present work concerns investigations on the mechanism of the chemical and electrochemical intercalation process. It is shown that two nonstoichiometric phases and one line phase are formed as intermediates with different kinetics. Carbon dioxide was found to be an efficient inhibitor for the O 2 uptake reaction. Several models are discussed in order to explain the phenomenon of fast oxygen anion transport at low temperatures.

Formation of lanthanum cobalt oxide (LaCoO3) highly dispersed on zirconium dioxide

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFormation of lanthanum cobalt oxide (LaCoO3) highly dispersed on zirconium dioxideNoritaka Mizuno, Hiroaki Fujii, Hiroshi Igarashi, and Makoto MisonoCite this: J. Am. Chem. Soc. 1992, 114, 18, 7151–7158Publication Date (Print):August 1, 1992Publication History Published online1 May 2002Published inissue 1 August 1992https://doi.org/10.1021/ja00044a030RIGHTS & PERMISSIONSArticle Views441Altmetric-Citations41LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Lanthanum cobalt oxide oxidation catalysts derived from mixed hydroxide precursors

Simultaneous oxidation/co-precipitation of an equimolar mixture of La(III) and Co(II) nitrates afforded a hydroxide-containing gel, which was converted to LaCoO 3 on calcination at 600°C. A material with surface area in excess of 40 m 2/g has been produced, provided the hydroxide gel was washed with a nonaqueous solvent before dehydration. The resultant LaCoO 3 perovskite sintered readily on heating above 700°C. Rates for oxidation for CO and propane showed a linear dependence upon the surface area of LaCoO 3 in the temperature range RT to 600°C.

X-ray photoelectron spectroscopy study of perovskite-type mixed oxides (La1?x A x ? CoO3)

The surface states of the perovskite-type cerium-, thorium- and strontium-doped lanthanum cobalt oxides (La1−xCexCoO3), La1−xThxCoO3, La1−xSrxCoO3x = 0 to 0.03) have been investigated using X-ray photoelectron spectroscopy (XPS). The binding energy differences (ΔBE) between Co2p3/2 and 01s of lattice oxygen have a maximum value atx = 0.02 in both La1−xCexCoO3 and La1−xThxCoO3. From this result, it is expected that the bonding state between the surface cobalt and lattice oxygen is mostly ionic at this point. The valence band (VB) spectra change greatly atx = 0.02 in both cerium- and thorium-doped samples. We speculate that the high spin trivalent cobalt ion is dominant atx = 0.02 on the surface. On the other hand, the ABEs between Co2p3/2 and 01s of lattice oxygen decrease with increasingx in La1−xSrxCoO3. It is expected that the bonding states become covalent in proportion tox. The change of the VB spectra for La1−xSrxCoO3 near the Fermi level (EF) can be explained by the formation of the impurity level.

Catalytic properties and surface states of La1-x Ce x CoO3

The surface chemical states of the perovskite-type thorium- or strontium-doped lanthanum cobalt oxides (La1−x Th x CoO3, La1−x Sr x CoO3) have been investigated using X-ray photoelectron spectroscopy. Catalytic oxidations of CO have been also investigated by flow methods. The ionicity between cobalt and lattice oxygen was increased by substituting thorium for lanthanum, and had a peak atx = 0.02. The catalytic activity also had a peak atx = 0.02. However, the ionicity decreased for the case of strontium substitution, and the activity also decreased.

Surface characterization and catalytic properties of La1?x -Sr x CoO3

The surface chemical states of the perovskite-type compounds, strontium doped lanthanum cobalt oxides (La1−xSrxCoO3), have been investigated using X-ray photoelectron spectroscopy (XPS). Catalytic oxidations of both methane and CO have also been investigated using flow methods. The chemical composition of the surface of La1−xSrxCoO3 was very different from that in the bulk, which was measured by X-ray fluorescence spectroscopy (XRFS). The catalytic activity of La1−xSrxCoO3 increased with an increase in the quantity of cobalt atoms on the surface.

Auger parameter in X-ray photoelectron spectroscopy of perovskite-type mixed oxides (La 1- xM xCoO 3, x=0-0.5, M: Ce, Sr)

The increase in the Auger parameter of oxygen atoms of the partly substituted lanthanum cobalt oxides (La 1- x M x CoO 3, x=0-0.5, M: Ce, Sr) corresponds to the increase of the catalytic activity of the oxides in the oxidation of methane. The increase in the Auger parameter of oxygen atoms is correlated with the increase of the electronegativity of acceptor site cations (La 1- x M x ). These results suggest that the catalytic activity of homogenous semiconductive catalysis is dominated by a collective property such as the dielectric constant of the material.

Promising catalyst for auto exhaust.

Lanthanum cobalt oxide as potential auto exhaust catalyst from studies of activity in gas phase