X‐ray absorption spectroscopic studies of Mn atoms in La_1−xSr_xMnO_3+δ compounds

Abstract

Mn K-edge x-ray absorption spectroscopy was used to determine the local structure at the Mn site in LaMnO 3 , La 0.7 Sr 0.3 MnO 3 and La 0.5 Sr 0.5 MnO 3 samples. The x-ray absorption near-edge spectra (XANES) show an intermediate oxidation state of the Mn atoms, the edge position indicating an average valence of ∼3.4 for the LaMnO 3 sample and an average valence of ∼3.7 for the La 0.7 Sr 0.3 MnO 3 and La 0.5 Sr 0.5 MnO 3 samples. Extended x-ray absorption fine structure (EXAFS) analyses show that the local order around Mn atoms in the La 0.7 Sr 0.3 MnO 3 sample can be described as a regular MnO 6 octahedron or as a distorted octahedron with two different Mn -O bond lengths. With regard to the La 0.5 Sr 0.5 MnO 3 sample, the local structure around Mn atoms is appropriately described by a regular MnO 6 octahedron. For this sample, the mean Mn -O bond length is shorter and is similar to that of Mn -O in the SrMnO 3 .

Jahn–Teller Disproportionation Induced Exfoliation of Unit‐Cell Scale ϵ‐MnO2

“…Thew hite-line peaks of Mn, which is corresponding to the core 1s electron excited to unoccupied 4p states,s hows ap ositive shift to high energy,i ndicating the higher valance states of LSMO-10 ha nd MnO 2 than that of LSMO. [35,36] These phenomena provide the evidence of disproportionation of Mn 3+ during etching process,w hich is consistent with the result of Mn L-edges.T he Fourier transformed EXAFS (FT-EXAFS) are further investigated to confirm their local geometric structure (Figure 2d). There are two peaks locating at 1.50 and 3.41 ,w hich can be observed from the FT-EXAFS curve of LSMO,corresponding to the Mn-O and Mn-Mn/La/Sr bonds in perovskite,r espectively.…”

“…There are two peaks locating at 1.50 and 3.41 ,w hich can be observed from the FT-EXAFS curve of LSMO,corresponding to the Mn-O and Mn-Mn/La/Sr bonds in perovskite,r espectively. [36] After treatment with HNO 3 for 10 h, the FT-EXAFS curve shows lower Mn-Mn bond compared to that of LSMO,i ndicating the reconstruction of perovskite structure.T he e-MnO 2 shows similar shape of FT-EXAFS curve to LSMO-10 he xcept for the increased coordination number of Mn-O and Mn-Mn. Compared with d-MnO 2 ,w ec an conclude that the two main peaks located at 2.65 and 2.99 can be attributed to edgesharing and corner-sharing Mn-Mn bond of MnO 6 octahedron, respectively, [37,38] implying the structural reconstruction of MnO 6 octahedron from corner-sharing to edge-sharing.…”

Photon energy dependent photoemission study of La0.7Sr0.3MnO3

“…However, while the spin-resolved photoemission study of the thin film La 0.7 Sr 0.3 -MnO 3 has shown half-metallic behaviour [5], other investigations of single crystals of the same composition have found spin-polarization lower than 100%, as one would expect for a half-metal [6]. Although many photoemission studies have been performed for polycrystalline samples, thin films and, more recently, single crystals of La 1Àx Sr xMnO 3 [7][8][9][10][11][12][13][14], their electronic structure is not yet fully understood.…”

Local tetragonal distortion inLa0.7Sr0.3MnO3straine

“…In the metallic La 0.7 Sr 0.3 MnO 3 compound, the e g electron is delocalized and the contribution of the spontaneous energy-lowering Jahn-Teller distortion of the Mn 3+ O 6 18,19 does not give rise to a measurable average distortion of the octahedra. In X-ray absorption spectroscopy (XAS) the coordination shell around Mn atoms can be modelled with one unique Mn − O distance at ≈1.94Å 20,21 .…”