Song Jia, Ning De, Bouwmeester Henny J M
Electrochemistry Research Group, Membrane Science and Technology, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands.
Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin, Germany.
Phys Chem Chem Phys. 2020 Jun 4;22(21):11984-11995. doi: 10.1039/d0cp00247j.
Structural evolution, electrical conductivity, oxygen nonstoichiometry and oxygen transport properties of perovskite-type oxides La0.6A0.4FeO3-δ (A = Ca, Sr, and Ba) were investigated. La0.6Ca0.4FeO3-δ (LCF64) and La0.6Sr0.4FeO3-δ (LSF64) show a phase transformation in air at elevated temperature, i.e., from orthorhombic (Pnma) to rhombohedral (R3[combining macron]c) and from rhombohedral to cubic (Pm3[combining macron]m), respectively, while La0.6Ba0.4FeO3-δ (LBF64) remains cubic over the entire temperature range from room temperature to 1000 °C. The different phase behaviour of the solids is interpreted to reflect the decreased tendency for octahedral tilting with increasing alkaline-earth-metal dopant ion radius. The electrical conductivity of LSF64 is 191 S cm-1 in air at 800 °C, decreasing to a value of 114 S cm-1 at a pO2 of 0.01 atm, and found over this pO2 range roughly twice as high as those of LCF64 and LBF64. Failure to describe the data of electrical conductivity using Holstein's small polaron theory is briefly discussed. Chemical diffusion coefficients and surface exchange coefficients of the materials in the range 650-900 °C were extracted from data of electrical conductivity relaxation. Data of oxygen nonstoichiometry was used to calculate the vacancy diffusion coefficients from the measured chemical diffusion coefficients. The calculated migration enthalpies are found to decrease in the order LCF64 (1.08 ± 0.04 eV) > LSF64 (0.95 ± 0.01 eV) > LBF64 (0.81 ± 0.01 eV). The estimated ionic conductivities of the materials, at 900 °C, are within a factor of 1.4.
研究了钙钛矿型氧化物La0.6A0.4FeO3-δ（A = Ca、Sr和Ba）的结构演变、电导率、氧非化学计量比和氧传输性能。La0.6Ca0.4FeO3-δ（LCF64）和La0.6Sr0.4FeO3-δ（LSF64）在空气中高温时分别发生相变，即从正交晶系（Pnma）转变为菱面体晶系（R3[combining macron]c）以及从菱面体晶系转变为立方晶系（Pm3[combining macron]m），而La0.6Ba0.4FeO3-δ（LBF64）在从室温到1000°C的整个温度范围内均保持立方晶系。固体的不同相行为被解释为反映了随着碱土金属掺杂离子半径增加，八面体倾斜趋势的降低。LSF64在800°C空气中的电导率为191 S cm-1，在pO2为0.01 atm时降至114 S cm-1的值，并且发现在该pO2范围内大致是LCF64和LBF64的两倍。简要讨论了使用霍尔斯坦小极化子理论描述电导率数据时的失败情况。从电导率弛豫数据中提取了材料在650 - 900°C范围内的化学扩散系数和表面交换系数。利用氧非化学计量比数据从测量的化学扩散系数计算空位扩散系数。发现计算出的迁移焓按LCF64（1.08±0.04 eV）> LSF64（0.95±0.01 eV）> LBF64（0.81±0.01 eV）的顺序降低。在900°C时，材料的估计离子电导率相差1.4倍。
