Local distortion of MnO6 octahedron in La1-xSrxMnO3+delta (x=0.1-0.9): an EXAFS study

Devi Ahilya University, Indore, Indaur, Madhya Pradesh, India
Journal of Physics Condensed Matter (Impact Factor: 2.22). 09/2005; 17(41):6393. DOI: 10.1088/0953-8984/17/41/010
Source: arXiv

ABSTRACT Room-temperature Mn K-edge extended x-ray absorption fine structure (EXAFS) studies were carried out on La1−xSrxMnO3+δ (x = 0.1–0.9) compounds. It is found from the detailed EXAFS analysis that the local structure around Mn sites is different from the global structure inferred from x-ray diffraction, especially for x≤0.4, indicating the presence of local distortions in MnO6 octahedra. For the rhombohedral compounds, x = 0.1 to 0.3, the distortion is maximum for x = 0.1 and two bond lengths are seen: a short one in the basal plane and a long one in the apical plane. For compounds with x = 0.4–0.8 two short bonds in the basal plane and four long bonds (two in the basal plane and the remaining two in the apical plane) are seen. For the compounds with compositions up to x = 0.3, the long bond length decreases and the short bond length increases with increase in x, whereas for the compounds with 0.4≤x≤0.8 both types of bond length decrease. Such behaviour of bond lengths is an indication of the changed nature of distortion from Jahn–Teller type to breathing type at x = 0.4 composition.

1 Bookmark
  • [Show abstract] [Hide abstract]
    ABSTRACT: Evolution of the Mn K-edge x-ray absorption near edge structure (XANES) in Pr(0.6)Ca(0.4)MnO(3) at pulsed magnetic fields has been investigated. A small enhancement of XANES spectra is detected across the magnetic-field-induced transition from the charge- and orbital-ordered (COO) insulator to ferromagnetic metal at 20 K. It is found that the magnetic-field dependence of the enhancement shows clear hysteresis, as seen in the magnetization with metamagnetic transition, suggesting a significant correlation between the change in the XANES and the field-induced collapse of the COO state. The enhancement of the absorption can be explained by an increase of the 4p density of states due to a reduction of hybridization between the 4p state of the central Mn ion with the core hole and the neighboring Mn 3d state. Local structural change around Mn ions is expected to modify the strength of the hybridization.
    Journal of Physics Condensed Matter 01/2009; 21(1):016006. DOI:10.1088/0953-8984/21/1/016006 · 2.22 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: La(0.5)Ba(0.5)MnO(3) nanocubes and nanoparticles were synthesized by hydrothermal and co-precipitation methods, respectively. The catalytic performances and thermal stabilities of the samples in the oxidation of CO and CH(4) were evaluated. La(0.5)Ba(0.5)MnO(3) nanocubes showed much higher catalytic activity and thermal stability in CO and CH(4) oxidation compared with the nanoparticles. After running at 560 degrees C for 50 h under the reaction conditions in CH(4) oxidation, the surface area of the nanoparticles decreased significantly, while the nanocubes well maintained their surface area. Jahn-Teller effect had a significant influence on the catalytic performances of La(0.5)Ba(0.5)MnO(3) nanocubes and nanoparticles. The much higher catalytic activity and thermal stability of La(0.5)Ba(0.5)MnO(3) nanocubes were mainly predominated by the perfect single crystal structure. (C) 2010 Elsevier B.V. All rights reserved.
    Applied Catalysis B Environmental 06/2010; 96(3-4-3-4):267-275. DOI:10.1016/j.apcatb.2010.01.025 · 6.01 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Nanocrystalline powders of a manganite compound in the series of La0.7A0.3MnO3 (LA3M), where A is Ca2+, Na1+, Sr2+ or Ba2+ are synthesized by a simple thermal decomposition method using related acetate salts as starting materials in aqueous solution. The precursors are analyzed by Thermogravimetric/Differential Thermogravimetric Analyzer (TG-DTG) techniques and then all of synthesized nanopowders are characterized at room temperature using X-ray diffraction (XRD) and X-ray absorption fine structure (EXAFS) techniques. The initial structural characterization shows that all the prepared samples exhibit non-stoichiometric perovskite structures. Only the La0.7Na0.3MnO3 (LN3B) sample contains oxygen deficiencies, whereas most samples contain excess oxygen, which results in cation vacancies in either the A- or B-site. The three regions of the crystal-structure transition are observed with variation of the average cationic radius in the A-site (〈r A 〉). The orthorhombic structure is observed when a smaller cation (Ca2+) is substituted for La3+. Likewise, the cubic structure is only obtained after substitution by the much larger Ba2+ ion, whereas the rhombohedral structure is still exhibited after substitution by Na1+ and Sr2+. The different structures are affected by the ionic radii of the A ion and the Mn4+ ion. Jahn–Teller distortions in the MnO6 octahedra composed of unequal $d_{\mathrm{Mn}\mbox{--}\mathrm{O}}$ in two or three bond lengths is observed for all samples except the LB3M sample, which exhibits equal $d_{\mathrm{Mn}\mbox{--}\mathrm{O}}$ values. The increasing of 〈r A 〉 can decrease this MnO6 distortion by shrinking the $d_{\mathrm{Mn}\mbox{--}\mathrm{O}}$ in the long bonds and stretching the $d_{\mathrm{Mn}\mbox{--}\mathrm{O}}$ in the short bonds; the distortion begins to vanish as 〈r A 〉≥1.292 Å.
    Journal of Superconductivity and Novel Magnetism 10/2012; 25(7). DOI:10.1007/s10948-012-1678-y · 0.93 Impact Factor

Full-text (2 Sources)

Available from
Jun 1, 2014