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Title: New RMnO{sub 3+δ} (R=Y, Ho; δ≈0.35) phases with modulated structure

A series of hexagonal RMnO{sub 3} (R=Y, Ho–Lu) compounds are first annealed in various highly oxidizing conditions to show that for the largest R constituents, Y and Ho, it is possible to load the phases with large amounts of excess oxygen. Within the oxygen-annealed samples we identify new heavily-oxygenated phases, that is, YMnO{sub 3.35} and HoMnO{sub 3.34}. The former is then thoroughly characterized by thermogravimetric analysis, X-ray diffraction and electron diffraction. These studies evidence a hexagonal sub-cell (a{sub S}≈3.578 Å (a{sub H}/√(3)), c{sub S}≈11.18 Å, space group P6{sub 3}mc) and satellites, associated with two modulation vectors q{sup →}{sub 1}{sup ⁎}≈0.41a{sup →}{sub S}{sup ⁎}+0.41b{sup →}{sub S}{sup ⁎}+1/3c{sup →}{sub S}{sup ⁎}andq{sup →}{sub 2}{sup ⁎}=(1/2). The results are interpreted by the formation of a modulated composite structure, resulting from the evolution of the hexagonal parent YMnO{sub 3+δ} structure toward a reduced pyrochlore-type structure Y{sub 2}Mn{sub 2}O{sub 7−x}, in long- and short-range ordering. - Graphical abstract: Hexagonal RMnO{sub 3+δ} phases are commonly taken as oxygen-stoichiometric. Here we show that the R=Y and Ho phases can be loaded with excess oxygen up to δ≈0.35 through high-pressure oxygenation annealing. Formation of a new composite structure composed of hexagonal-like RMnO{sub 3+δ} and pyrochlore-like RMnO{sub 3.5−δ} constituents ismore » demonstrated in the case of R=Y. - Highlights: • Hexagonal RMnO{sub 3+δ} phases are commonly taken as oxygen-stoichiometric. • For R=Y and Ho phases excess-oxygen loading is possible. • Single-phase samples with a new composite structure are obtained at δ≈0.35. • The new structure is composed of hexagonal- and pyrochlore-like units.« less
Authors:
 [1] ; ;  [2] ;  [1] ;  [1]
  1. Department of Chemistry, Aalto University, FI-00076 Aalto (Finland)
  2. Laboratoire CRISMAT, ENSICAEN, Caen (France)
Publication Date:
OSTI Identifier:
22443485
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 221; Other Information: Copyright (c) 2014 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ANNEALING; ELECTRON DIFFRACTION; HEXAGONAL LATTICES; HOLMIUM COMPOUNDS; MANGANATES; MANGANESE OXIDES; OXYGEN; PYROCHLORE; SPACE GROUPS; THERMAL GRAVIMETRIC ANALYSIS; X-RAY DIFFRACTION; YTTERBIUM COMPOUNDS