Influence of Phase Transformations on Crystal Growth of Stoichiometric Brownmillerite Oxides: Sr2ScGaO5 and Ca2Fe2O5

Abstract

High quality stoichiometric brownmillerite-type oxide single crystals have been successfully grown by the floating zone method using a mirror furnace. We report here on the growth conditions and structural characterization of two model compounds: Ca 2 Fe 2 O 5 and Sr 2 ScGaO 5 . Both show oxygen deficiency with respect to the average perovskite structure, and are promising candidates for oxygen ion conductivity at moderate temperatures. While Sr 2 ScGaO 5 single crystals were obtained in the cubic oxygen-deficient perovskite structure, Ca 2 Fe 2 O 5 crystallizes in the brownmillerite framework. Having no cubic parent high temperature counterpart, Ca 2 Fe 2 O 5 crystals were found to be not twinned. We report on structural characterization of the as-grown single crystals by neutron and X-ray diffraction, as well as scanning electron microscopy (SEM) coupled with EDX (Energy Dispersive X-Ray Spectroscopy) analysis and isotope exchange experiments.

Photoactive Brownmillerite Multiferroic KBiFe2O5 and Its Potential Application in Sunlight-Driven Photocatalysis

“…26,35 Brownmillerite characteristic peak of (110) was found to be absent for 550 °C synthesized sample (K5), whereas it was observed for both K6 and K7 (750 °C) samples. 11 Morphology of the as-prepared samples was investigated by SEM. The corresponding image of K5 sample (non-brownmillerite phase) showed irregular morphology with no defined structures.…”

“…A 2 B 2 O 5 -like structures possess oxygen deficiency along the [110] direction and corner-sharing BO 6 octahedra alternate with rows of corner-sharing BO 4 tetrahedra. 11−14 Typically, Fe-based brownmillerite compounds contain FeO 4 tetrahedra leading to the occurrence of lower band gaps unlike Fe-based perovskites, which consist of FeO 6 octahedra only. 15 The lower band gap of Fe-based brownmillerite compounds is attributed to the presence of shorter Fe–O bond lengths and high covalence in FeO 4 tetrahedron compared to FeO 6 octahedron.…”

Correlation between Structural and Transport Properties of Ca-Doped La Nickelates and Their Electrochemical Performance

“…Oxides with a perovskite-related Ruddlesden-Popper (R-P) structure, particularly Ln 2 NiO 4+δ (Pr, Nd, La), have been reported to have high levels of mixed ionic and electronic conductivity in addition to fast oxygen transport [1][2][3][4][5]. Such properties are among the main requirements for oxygen separation membranes and air electrodes of intermediate temperature electrochemical devices [6][7][8][9][10][11].…”

Analysis of the electrical transport, conductivity, and dielectric relaxation behavior of La0.75 Ba0.10 Sr0.15 Fe O2.875-δ (δ = 0.375 and 0.50) brownmillerite oxides

“…Indeed, they exhibit a mixed ionic and electronic conductivity [2]. Besides, these ceramics are promising materials for a wide range of technological applications [3][4][5][6][7]. Moreover, ferroelectrics oxides are gaining much popularity in recent years in view of their high colossal dielectric constant (ε' 10 3 ) [8].…”