Floating-zone growth of brownmillerite Sr2Fe2O5 and the observation of a chain-ordered superstructure by single-crystal neutron diffraction

Order, Disorder, and Dynamics in Brownmillerite Sr2Fe2O5

“…In both cases, the indexing routine identified two primitive orthorhombic lattices whose dimensions agreed well with the lattice parameters of the Pbma brownmillerite supercell identified in Ref. 22. The reciprocal lattices of the two cells were related by an 88.5° rotation around b* and can thus be assigned to Twins A and D as defined in Figure 2.…”

“…Confirmation of the observed (h, 2k+1, h)B or (2h, 2k+1, h) reflections as purely magnetic contradicts the earlier claim 22 that the appearance of these reflections in Figure 3(a) supported the existence of the Pbma supercell in Sr2Fe2O5. However, the diffraction image in the perpendicular plane (presented in the same article, Figure 4 and in Ref.…”

“…The presence of modulated order in Sr2Fe2O5 was further supported by subsequent neutron diffraction studies on single-crystals grown by the floating-zone method, which were reportedly dominated by the commensurate (α = ½, β = 0) Pbma superstructure on the length scale of neutron diffraction. 11,22 The Pbma structure was also found to be the thermodynamic ground state of Sr2Fe2O5 by density functional theory (DFT) calculations. 23 However, the Icmm long-range approximation was claimed to be more consistent with the results of a synchrotron x-ray diffraction experiment on small (~70 µm) fragments of similarly grown crystals.…”

“…[010]-paired twins but achieve partial or full elimination of the other, orthogonal [010]-pair that was present in neutron diffraction images of the FZ-grown crystal rod. 22 Notably, the slightly larger (~70 µm) crystal used by Maity et al 12 also contained the four twins observed in the bulk rod, suggesting that this scale represents an approximate lower bound for the interleaving of orthogonal [010] twin pairs in FZ-grown crystals of Sr2Fe2O5.…”

A new defect chemistry model for Nb-doped SrCoO2.5+δ: The role of oxygen interstitials and delocalized-to-localized electron holes

“…Furthermore, these ordered oxygen vacancies have also been considered as good candidates for anion intercalation such as O 2and Fwith a full occupation of the vacant sites to yield a simple perovskite structure [29][30][31] . Aukett et al further confirmed by Lorentzian broadening of the quasielastic neutron scattering spectrum that induced rotations of BO 4 by higher temperatures are a precondition for moving oxide-ion into tetrahedral layers from the octahedral layers 32,33 , creating oxideion conduction pathways and activating long-range diffusion at the interface between layers; the latter is thought to be the driving force for oxygen vacancies disorder and isotropic oxygen diffusion. was given in their original paper why ( ) was chosen as a point defect.…”