Synthesis and structural characterization of La{sub x}Sr{sub 1-x}MnO{sub 2.6+{delta}} (0.1<x<0.4) compounds displaying compressed octahedral coordination of Mn{sup (4-5x)+}
- Cryssmat-Lab/Catedra de Fisica/Detema, Facultad de Quimica, Universidad de la Republica, P.O. Box 1157, Montevideo (Uruguay)
- Physics Department, Northern Illinois University, DeKalb, IL 60115 (United States)
La{sub x}Sr{sub 1-x}MnO{sub 2.6+{delta}} (x=0.1-0.4) compounds have been obtained by low-temperature annealing of stoichiometric materials in hydrogen. La{sub 0.1}Sr{sub 0.9}MnO{sub 2.6+{delta}} ({delta}=0.15) and La{sub 0.3}Sr{sub 0.7}MnO{sub 2.6}, tetragonal (P4/m), and La{sub 0.2}Sr{sub 0.8}MnO{sub 2.6,} pseudo-tetragonal monoclinic (P2/m), structures are isostructural with oxygen-vacancy-ordered Sr{sub 5}Mn{sub 5}O{sub 13} (a=b{approx}{radical}(5)a{sub P}, c{approx}a{sub P}). La{sub 0.4}Sr{sub 0.6}MnO{sub 2.6} shows cubic perovskite structure with disordered oxygen vacancies. In the vacancy-ordered (La{sub x}Sr{sub 1-x}){sub 5}Mn{sub 5}O{sub 13} phases four out of five Mn cations are Mn{sup 3+} and show a typical Jahn-Teller elongated pyramidal coordination while the fifth one Mn{sup (4-5x)+}, in octahedral environment, shows decreasing formal charge from Mn{sup 4+} (x=0) to Mn{sup 2.5+}x=0.3. This unusual selective doping of the octahedral site produces structural strain due to increasing size of the Mn{sup (4-5x)+} and, in the case of (La{sub 0.2}Sr{sub 0.8}){sub 5}Mn{sub 5}O{sub 13}, the unusual compressed octahedral arrangement of oxygen atoms around it. The coordination geometry implies that either the d{sub x{sup 2}-y{sup 2}} orbital is occupied, which would be a rare example of inverted occupancy of e{sub g} orbitals in manganites, or that disordered Mn{sup 3+} apically elongated MnO{sub 6} octahedra are present with normal electronic configuration d{sub t{sub 2}{sub g}}{sup 3}d{sub x{sup 2}-y{sup 2}}{sup 0}d{sub z{sup 2}}{sup 1}, and the observed bond distances are the average of the long and intermediate in-plane Mn-O bonds. Several structural features favor the second case. - Abstract: La{sub x}Sr{sub 1-x}MnO{sub 2.6} compounds (0.1{<=}x{<=}0.4) show a structural phase transition from Sr{sub 5}Mn{sub 5}O{sub 13}-type oxygen-vacancy-ordering (x{<=}0.3) to vacancy-disordered x=0.4, showing clear indications of short-range ordering. Compressed MnO{sub 6} octahedra are observed for Mn{sup 3+}-containing x=0.2 compound that is probably consequence of the presence of elongated MnO{sub 6} octahedra with the long-axis disordered in the x-y plane . Display Omitted.
- OSTI ID:
- 21212176
- Journal Information:
- Journal of Solid State Chemistry, Vol. 182, Issue 1; Other Information: DOI: 10.1016/j.jssc.2008.10.020; PII: S0022-4596(08)00537-9; Copyright (c) 2008 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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