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(4-5x)+.
- Materials Science Division
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}5a{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 1{sub 2{sub g}}}{sup 3}d{sub x{sup 2}-y{sup 2}}{sup 0}d{sub z{sup 3}}{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.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); National Science Foundation (NSF); DOT
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 1009342
- Report Number(s):
- ANL/MSD/JA-68800; TRN: US201106%%535
- Journal Information:
- J. Solid State Chem., Vol. 182, Issue 1 ; Jan. 2009
- Country of Publication:
- United States
- Language:
- ENGLISH
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