Oxygen vacancy ordering in SrFe_0.25Co_0.75O_2.63perovskite material

Abstract

SrFeCoO was synthesized by a solid-state reaction. Its structural study at room temperature using conventional X-ray as well as neutron powder diffraction, electron diffraction and high-resolution transmission electron microscopy is presented. An oxygen-vacancy ordering related to the "314" model known for the SrYCoO oxide is proposed despite neither an A-site ordering nor an A-site mismatch. By means of Mössbauer spectroscopy, Mohr salt titration and the difference in the neutron cross sections of Fe and Co, a cation distribution within the crystallographic sites as the following Sr(FeCo)(FeCoCo)O is suggested, highlighting a natural layered structure with Fe and Co in higher oxidation states in the oxygen replete layers than in the oxygen deficient ones.

Perovskite‐Derived Layered Crystal Structure in SrCo0.26Fe0.74O3‐δ Thin Films

“…It is possible that the experimental result has characteristics of both 314-SrBO 2.625 or P L -SrBO 2.5 , i.e., a structure with alternating layers of octahedral and mixed B-site coordination. The discrepancy between the observed Sr-Sr distance ratio ≈1.4 and the calculated value ≈1.2 may be affected by epitaxial strain: the Sr-Sr distance ratio calculated from bulk unstrained 314-structured SrFe 0.25 Co 0.75 O 2.63 is ≈1.1, [37] smaller than our calculated value of ≈1.2 for tensilestrained supercells.…”

“…Figure 3 summarizes the experimental and theoretical structures reported on SrBO 3-𝛿 compounds with respect to two variables, 𝛿 from 0 to 0.5 and B = Co, Fe, or Mn. [4,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38] In order to understand the ordering of oxygen ions in our SCFO films and compare with the structures reported in Figure 3, we considered the simulated STEM images of eight different structures named SrBO 3 , P L -SrBO 2.75 , BM-SrBO 2.75 , 314-SrBO 2.625 , BM-SrBO 2.625 , P L -SrBO 2.5 , BM-SrBO 2.5 , and SrBO 2 , as depicted in Figure 4. These structures were selected because they have periodic oxygen deficiency in the B-coordinated layers along the [001] direction (i.e., film growth direction).…”

“…SrCoO 2.75 thin films are expected to prefer random V O locations from DFT modeling, [ 35 ] however, a unique ordering can be observed when δ = 0.25 and 0.18 in SrCoO 3‐δ . [ 36 ] A 314‐type ordering named after the cation stoichiometry in Sr 3 Y 1 (Co,Fe) 4 O 10.5 has been observed in SrFe 0.25 Co 0.75 O 2.63 , [ 37 ] and V O ordering in layers has been observed in Nb‐doped Sr(Co,Fe)O 3‐δ , where Nb 5+ is believed to prevent BM formation, [ 38 ] both of them in the bulk form.…”