Determination of oxygen nonstoichiometry in SrFeO_3−δ by solid‐state Coulometric titration

Abstract

The oxygen nonstoichiometry of SrFeO3−δ was determined by solid‐state Coulometric titration at 750°C‐1040°C and 10−18≤pO2(atm)≤0.5. At T≤850°C, a hysteresis in the oxygen nonstoichiometry (δ) isotherms indicates the presence of a two‐phase region corresponding to a mixture of a perovskite and an oxygen vacancy ordered phase. The variation of δ with temperature at fixed pO2 values and the variation of log(pO2) with reciprocal temperature at fixed δ are reported. The pO2 at the p‐n transition in the electrical conductivity increases as the temperature increases, and the transition in the conductivity isotherm occurs at a composition of SrFeO2.505(1) at 950°C and SrFeO2.508(1) at 900°C. Since strontium exclusively occupies the A‐site, a simple point defect model that assumes noninteracting defects can describe the isotherms but only at 1040°C; nonideal behavior is observed at lower temperatures. The partial molar thermodynamic quantities for oxygen in SrFeO3−δ were determined.

Isothermal relaxation kinetics for the reduction and oxidation of SrFeO3 based perovskites

“…The oxygen non-stoichiometry d, decreases with temperature, 3 but has been found to persist at relatively low temperatures, T o 673 K. 4 For this reason SrFeO 3 based perovskites have been extensively investigated as oxygen storage materials, which can be utilized in oxygen separation and production processes. [5][6][7][8] These processes operate via a redox cycle, where oxygen is absorbed in an oxidation step and released again in a reduction step.…”

“…In previous studies equilibrium measurements have typically focused on high temperatures 773-1473 K. 1,3 There is some limited data at lower temperatures, 4,6 but in the present study we aim to have a broader set of equilibrium data at lower temperatures, so that we know more accurately what the final equilibrium non-stoichiometry should be when the reactions are complete (d N in eqn (3)).…”

“…The perovskite oxide SrFeO 3 exhibits an oxygen non-stoichiometry which depends on the temperature and partial pressure of oxygen, [1][2][3]…”

Phase equilibria, structure, oxygen nonstoichiometry, and thermal expansion of oxides in the 1/2Y2O3–SrO–1/2Fe2O3 system

“…Most of the available data are devoted to partially substituted lanthanum ferrites or, in some cases, to ferrites with other large‐ and middle‐sized rare earth elements (Pr–Gd). The information concerning small‐sized rare earth‐ or yttrium‐based ferrites is limited, although undoped strontium ferrite and yttrium ferrite have been the objects of wide‐ranging studies as magnetic and membrane materials in the last few decades . The wide variety of specific features of phase formation in the related systems and significant differences in the phase diagrams of these systems require detailed study of each system, in particular Y 2 O 3 –SrO–Fe 2 O 3 .…”

Progress in chemical looping-based transformations of small molecules

“…在低温条件下, 随着氧平衡分压不断降低, 立 . 从图11可以看出, 1040℃时氧化学计 量系数从2.56变化到2.49时, 氧平衡分压降低了约9个 数量级 [103] . 当氧化学计量系数降低到2.5时, SrFeO 2 另一个提高钙钛矿载氧体还原氧化性能的策略是 用其他离子部分取代A或/和B位离子 [107] .…”