Order-disorder phase transitions of excess oxygen atoms and their appearance as eutectoid and peritectoid reactions inLa2NiO4+δ(δ=0.047–0.116)crystals

AbstractNew forms of Sr-Co oxide with one-dimensional structures related to mixed-layer hexagonal perovskites have been synthesized and characterized by TEM. Crystals of Sr5Co2O12 grown from molten KOH flux and oxidized under slow cooling have structures based on a 3/2 ratio of mixed [Sr3CoO6] and [Sr3O9] layers. This is the first known structure with layers of this type stacked in a non-integer ratio, yielding chains of face-sharing octahedral and trigonal prismatic Co-sites with a 3 + 1 sequence along the c-axis. In oxygen-deficient Sr5Co2O12−x, the {110} structural modulation of the stoichiometric 5:4 phase becomes rotated to an irrational orientation, possibly in association with vacancy ordering, forming an incommensurate superstructure. For the compound Sr6Co5O15, previously known to have a 1/1 ratio of [Sr3CoO6] and [Sr3O9] layers with a 4 + 1 octahedral/trigonal prismatic site sequence, introduction of excess oxygen atoms leads to formation of a commensurate rhombohedral superlattice in which c is doubled relative to the stoichiometric 6:5 phase.

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A Channeling Study of the Structure of U4O9

Canadian Journal of Physics ◽

10.1139/p71-269 ◽

1971 ◽

Vol 49 (17) ◽

pp. 2215-2226 ◽

Cited By ~ 34

Author(s):

Hj. Matzke ◽

J. A. Davies ◽

N. G. E. Johansson

Keyword(s):

Critical Angle ◽

Fluorite Structure ◽

Recent Model ◽

The Other ◽

Excess Oxygen ◽

Wide Angle ◽

Oxygen Sublattice ◽

Other Hand ◽

Rutherford Scattering ◽

Oxygen Atoms

The channeling behavior of 1-MeV He+ ions and deuterons in U4O9 has been studied in order to provide information on the location of the excess oxygen in the fluorite structure of UO2. Wide-angle (Rutherford) scattering was used to study the channeling behavior with respect to the uranium sublattice, and the 16O(d, p)17O reaction was used to investigate the oxygen sublattice. A pronounced disorder in the oxygen sublattice was indicated by very poor channeling properties and strong dechanneling with increasing depth. The data are thus in conflict with the model incorporating the excess oxygen in the regular interstitial positions along the [Formula: see text] uranium rows; on the other hand, they are consistent with the more recent model of Willis in which the excess oxygen atoms are displaced ~ 1 Å from the regular interstitial sites and displace, in addition, some normal oxygen atoms. Channeling with respect to the uranium sublattice was found to be substantially the same as in stoichiometric UO2—but with a somewhat smaller critical angle, indicating that the uranium atoms may be displaced slightly (i.e. ~ 0.25 Å) by the presence of the excess oxygen.

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Phase diagram and effect of excess oxygen atoms on the spin and charge ordering inLa2NiO4+δcrystals

Physical Review B ◽

10.1103/physrevb.60.14841 ◽

1999 ◽

Vol 60 (21) ◽

pp. 14841-14846 ◽

Cited By ~ 4

Author(s):

Tôru Kyômen ◽

Masaharu Oguni ◽

Mitsuru Itoh ◽

Kenzô Kitayama

Keyword(s):

Phase Diagram ◽

Charge Ordering ◽

Excess Oxygen ◽

Spin And Charge Ordering ◽

Oxygen Atoms

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Investigations of the CO-Chemiluminescence in the Reaction of Ketene With Excess Oxygen Atoms

10.21236/ada381370 ◽

2000 ◽

Author(s):

Ghanshyam L. Vaghjiani

Keyword(s):

Excess Oxygen ◽

Oxygen Atoms

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Electron Microscopy of Graphite Intercalation Compounds

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100055564 ◽

1982 ◽

Vol 40 ◽

pp. 544-545

Author(s):

G. Timp ◽

L. Salamanca-Riba ◽

L.W. Hobbs ◽

G. Dresselhaus ◽

M.S. Dresselhaus

Keyword(s):

Electron Microscopy ◽

Phase Transitions ◽

Domain Wall ◽

Intercalation Compounds ◽

Lattice Plane ◽

Wall Model ◽

Graphite Intercalation Compounds ◽

Fundamental Symmetry ◽

Graphite Intercalation

Electron microscopy can be used to study structures and phase transitions occurring in graphite intercalations compounds. The fundamental symmetry in graphite intercalation compounds is the staging periodicity whereby each intercalate layer is separated by n graphite layers, n denoting the stage index. The currently accepted model for intercalation proposed by Herold and Daumas assumes that the sample contains equal amounts of intercalant between any two graphite layers and staged regions are confined to domains. Specifically, in a stage 2 compound, the Herold-Daumas domain wall model predicts a pleated lattice plane structure.

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