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: 2.35). 09/2005; 17(41):6393. DOI: 10.1088/0953-8984/17/41/010
Source: arXiv


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.

Download full-text


Available from: Sudhir Kumar Pandey, Oct 13, 2015
1 Follower
33 Reads
  • [Show abstract] [Hide abstract]
    ABSTRACT: The experimental Mn K-edge x-ray absorption spectra of La$_{1-x}$Sr$_x$MnO$_{3}$, $x$ = 0 - 0.7 are compared with the band structure calculations using spin polarized density functional theory. It is explicitly shown that there is a correspondence between the inflection point on the absorption edge and the centre of gravity of the unoccupied Mn 4$p$-band. This correspondence has been used to separate the doping and size contributions to edge shift due to variation in number of electrons in valence band and Mn-O bond lengths, respectively when Sr is doped into LaMnO$_3$. Such separation is helpful to find the localization behaviour of charge carriers and to understand the observed transport properties and type of charge carriers participating in the conduction process in these compounds.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Room temperature Co K edge extended x-ray absorption fine structure (EXAFS), x-ray absorption near edge structure (XANES), including the pre-edge structure, and x-ray diffraction (XRD) studies are carried out on LaCoO3 and PrCoO3. The Co–O, Co–La/Pr and Co–Co bond lengths are obtained from EXAFS analysis and compared with those obtained from XRD study. The EXAFS analysis of the data indicates that the CoO6 octahedron is distorted in both LaCoO3 and PrCoO3. There are two Co–O bonds with bond length 1.863 (1.886) Å and four Co–O bonds with bond length 1.928 (1.942) Å for LaCoO3 (PrCoO3). Such distortion is expected in orthorhombic PrCoO3 but not in rhombohedral LaCoO3. This distortion in the CoO6 octahedron is attributed to Jahn–Teller active Co3+ ions in an intermediate spin state in these compounds. Higher shell studies reveal that Debye–Waller (DW) factors of Co–Pr and Co–Co bonds in PrCoO3 are greater in comparison with those of Co–La and Co–Co bonds in LaCoO3, indicating that these bonds are structurally more disordered in PrCoO3. The comparison of Co–Co bond lengths and corresponding DW factors indicates that the structural disorder plays an important role in deciding the insulating properties of these compounds. XANES studies have shown changes in the intensities and positions of different near edge features. The comparison of experimental spectra with the calculated ones—using the Co 4p density of states obtained from local density approximation calculations and matrix elements calculated using an atomic like core state as the initial state and a confluent hypergeometric function as the final state—indicates that for orthorhombic structure, the intensities of different features are lower as compared to those for the cubic structure. The pre-edge peaks attributed to and transitions show the effects of hybridization of the eg orbitals with O 2p orbitals, and their relative intensities in PrCoO3 and LaCoO3, can be explained by using the average Co–O bond length obtained from the EXAFS.
    Journal of Physics Condensed Matter 11/2006; 18(47):10617. DOI:10.1088/0953-8984/18/47/008 · 2.35 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The detailed evolution of the magnitude of the local Jahn-Teller (JT) distortion in La(1-x)Ca(x)MnO3 is obtained across the phase diagram for 0< or =x< or =0.5 from high-quality neutron diffraction data using the atomic pair distribution function method. A local JT distortion is observed in the insulating phase for all Ca concentrations studied. However, in contrast with earlier local structure studies, its magnitude is not constant, but decreases continuously with increasing Ca content. This observation is at odds with a simple small-polaron picture for the insulating state.
    Physical Review Letters 03/2007; 98(13):137203. DOI:10.1103/PhysRevLett.98.137203 · 7.51 Impact Factor
Show more