Oxygen nonstoichiometry and defect equilibrium in the perovskite-type oxides La1-xSrxMnO3+d
Oxygen nonstoichiometry and defect equilibrium in the perovskite-type oxides La1-xSrxMnO3+d
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DOI：
10.1016/s0167-2738(99)00323-9
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发表时间：
2000-04-01
影响因子：
3.2
通讯作者：
Hashimoto, T
中科院分区：
文献类型：
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作者：
Mizusaki, J;Mori, N;Hashimoto, T
钙钛矿型氧化物固溶体La 1-xSrxMnO3的氧非化学计量除以d（x = 0 - 0.5）总结在873 - 1273 K下氧含量3 + d对log P（O-2）的曲线图中。对于小于或等于0.4的x，在图中观察到两个平台，一个在晶格位置的化学计量点附近，即（3 + d）= 3.00，另一个在低温和高P（O-2）下，在该温度下（3 + d）饱和。在后一平台区，Mn的平均价态为+3.3-3.4，与x无关，饱和氧含量随x的增加而线性下降。提出了一个缺陷模型，以合理化的（3 + d）与log P（O-2）的关系，以及报告的电子性能之间的两个平台，这是基于以下假设。(i)由于三价阳离子空位导致大的电子不平衡和局部晶格畸变，它们不会彼此靠近并且靠近Sr-La '位点。为了表示这些缺陷之间的间距，我们引入了空位的概念，不包括每个阳离子空位周围的空间和Sri。(ii)随着阳离子空位的形成，空位周围的氧离子形成非键合氧2p能级。所形成的能级是窄的，并且该能级中的电子的迁移率是低的。我们假设Mn的导电e（g）（向上箭头）能级和低迁移率t（2g）（向下箭头）能级彼此非常接近，并且这些能级低于非键合氧2p能级。这种非键合氧2p能级作为空穴陷阱。两个平台之间的（3 + d）对logP（O-2）的关系可以通过假设三价阳离子空位周围的空位体积和Sr-La '周围的空位体积分别为9个和3个准立方钙钛矿型ABO（3）的晶胞来解释。应用所提出的电子结构，缺氧组合物的非化学计量可以通过氧化物离子空位的随机分布来解释。然而，基于缺陷平衡的分析不能识别阳离子空位，无论它是La位还是Mn位还是La和Mn位，因为无论是什么阳离子空位，结果几乎相同。考虑到报道的中子衍射分析结果，我们报告了一个详细的分析放置的阳离子空位主要在La网站。(C)2000爱思唯尔科技有限公司。保留所有权利。
Oxygen nonstoichiometry of perovskite-type oxide solid solution La1-xSrxMnO3 divided by d (x = 0-0.5) is summarized in a plot of oxygen content, 3 + d, vs. log P(O-2) at 873-1273 K. For x less than or equal to 0.4, two plateaus are observed in the plot, one around the stoichiometric point as to the lattice site, i.e. (3 + d) = 3.00, and the other at low temperatures and high P(O-2) at which (3 + d) was saturated. At the latter plateau, the mean Mn valence was +3.3-3.4 independent of x and the saturated oxygen content decreased Linearly with increasing x. A defect model is proposed to rationalize the (3 + d) vs. log P(O-2) relationship as well as the reported electronic properties between the two plateaus, which is based on the following assumptions. (i) Because the trivalent cation vacancies cause a large electronic imbalance and local lattice distortion, they do not stay close to each other and close to the Sr-La' site. To express the spacing among these defects, we introduce the concept of a vacancy excluding space around each cation vacancy and Sri,. (ii) With the formation of cation vacancies, a nonbonding oxygen 2p level is formed by the oxide ions around the vacancies. The formed level is narrow and the mobility of electrons in this level is low. We assume that the conductive e(g)(up arrow) level and the low mobility t(2g)(down arrow) level of Mn are very close to each other and that these levels are lower than the nonbonding oxygen 2p level. This nonbonding oxygen 2p level serves as the hole-trap. The (3 + d) vs, log P(O-2) relationships between the two plateaus can be explained by assuming that the volume of the vacancy excluding space around a trivalent cation vacancy and that around Sr-La' are nine and three unit cells, respectively, of pseudo-cubic perovskite-type ABO(3). Applying the proposed electronic structure, nonstoichiometry of the oxygen-deficient composition could be explained by the random distribution of oxide-ion vacancies. However, analysis based on the defect equilibrium could not identify the cation vacancy site, whether it is a La site or a Mn site or both a La and Mn site, because the results are almost identical whatever the cation vacancy site. Considering the reported neutron diffraction analysis results, we report a detailed analysis placing the cation vacancies predominantly on the La site. (C) 2000 Elsevier Science B.V. All rights reserved.