Chemically induced expansion of La2NiO4+δ-based materials
Chemically induced expansion of La2NiO4+δ-based materials
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DOI：
10.1021/cm070096x
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发表时间：
2007-04-17
影响因子：
8.6
通讯作者：
Frade, Jorge R.
中科院分区：
文献类型：
--
作者：
Kharton, Vladislav V.;Kovalevsky, Andrei V.;Frade, Jorge R.
用控制气氛法研究了在923-1223 K、氧分压5 × 10 ~（-4）-0.7atm范围内，K_2NiF_4型结构的La_2Ni_（1-x）M_xO_（4 + δ）（M = Fe，Co，Cu; x = 0-0.2）混合导电体系中氧超化学计量比变化引起的平衡化学应变。结合库仑滴定法和热重分析法测量的氧含量，结果显示出非常低的化学膨胀率，有利于高温电化学应用。在氧化条件下，相对于大气压氧压的等温膨胀（ε（C））小于0.02%。这些值和相应的非化学计量增量之间的比率从-3 X 10（-3）变化到6 X 10（-3），这与衍生自类钙钛矿钴酸盐和铁氧体的大多数可渗透混合导体相比低得多。因此，在固定氧压（13.7-15.1）× 10（-6）K-1时，化学成分对表观热膨胀系数的贡献不超过5%。高温X射线衍射研究表明，这种行为的结果从强烈的各向异性膨胀的K2 NiF 4型晶格，即相反的变化的晶胞参数上改变氧的化学计量。
The equilibrium chemical strains induced by the oxygen hyperstoichiometry variations in mixed-conducting La2Ni1-xMxO4+delta (M = Fe, Co, Cu; x = 0-0.2) with K2NiF4-type structure, were studied by controlled-atmosphere dilatometry at 923-1223 K in the oxygen partial pressure range 5 x 10(-4) to 0.7 atm. In combination with the oxygen content measured by coulometric titration and thermogravimetry, the results reveal a very low chemical expansivity, favorable for high-temperature electrochemical applications. Under oxidizing conditions, the isothermal expansion relative to atmospheric oxygen pressure (epsilon(C)) is less than 0.02%. The ratio between these values and the corresponding nonstoichiometry increment varies from -3 x 10(-3) to 6 x 10(-3), which is much lower compared to most permeable mixed conductors derived from perovskite-like cobaltites and ferrites. Consequently, the chemical contribution to apparent thermal expansion coefficients at a fixed oxygen pressure, (13.7-15.1) x 10(-6) K-1, does not exceed 5%. The high-temperature X-ray diffraction studies showed that this behavior results from strongly anisotropic expansion of the K2NiF4-type lattice, namely the opposing variations of the unit-cell parameters on changing oxygen stoichiometry.