首页> 外文OA文献 >Oxygen Nonstoichiometry, Mixed Conductivity, and Mössbauer Spectra of Ln0.5A0.5FeO3−δ (Ln = La−Sm, A = Sr, Ba): Effects of Cation Size
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Oxygen Nonstoichiometry, Mixed Conductivity, and Mössbauer Spectra of Ln0.5A0.5FeO3−δ (Ln = La−Sm, A = Sr, Ba): Effects of Cation Size

机译:Ln0.5a0.5FeO3 - δ(Ln = La - sm,a = sr,Ba)的非化学计量氧,混合电导率和穆斯堡尔谱:阳离子尺寸的影响

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摘要

Increasing the difference of the Ln3+ and A2+ cation radii in perovskite-type Ln0.5A0.5FeO3−δ (Ln = La, Pr, Nd, Sm; A = Sr, Ba) results in higher oxygen deficiency and lower oxygen-ionic and p-type electronic conductivities, determined using the oxygen permeation and total conductivity measurements at 973−1223 K. The relationships between the anion transport and A-site cation size mismatch remain essentially similar in air and under reducing conditions when most iron cations become trivalent, thus confirming critical influence of oxygen-vacancy trapping processes induced by the lattice strain. At low temperatures, analogous correlation is also observed for quadrupole splittings derived from the Mssbauer spectra of oxygen-stoichiometric Ln0.5A0.5FeO3. Contrary to the ionic conductivity variations, the role of surface exchange kinetics as a permeation-limiting factor, evaluated from the membrane thickness dependence of oxygen fluxes, tends to decrease on Ba2+ doping and on decreasing Ln3+ size in Ln0.5Sr0.5FeO3−δ series. The n-type electronic conduction and low-p(O2) stability at 1223 K are substantially unaffected by the cation radius mismatch.
机译:钙钛矿型Ln0.5A0.5FeO3-δ(Ln = La,Pr,Nd,Sm; A = Sr,Ba)中的Ln3 +和A2 +阳离子半径之差的增加会导致缺氧增加,而氧离子和p降低氧渗透和总电导率测量值在973-1223 K时确定的电子类型电导率。在空气中以及大多数铁阳离子变为三价的还原条件下,阴离子迁移与A-位阳离子尺寸失配之间的关系基本上保持相似。证实了晶格应变引起的氧空位俘获过程的关键影响。在低温下,从氧化学计量的Ln0.5A0.5FeO3的Mssbauer光谱得出的四极分裂也观察到类似的相关性。与离子电导率变化相反,从氧通量的膜厚度依赖性评估表面交换动力学作为渗透限制因子的作用,在Ba2 +掺杂和Ln0.5Sr0.5FeO3-δ系列的Ln3 +尺寸减小中趋于减小。 n型电子传导和1223 K下的低p(O2)稳定性基本上不受阳离子半径失配的影响。

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