XPS investigation of Mn valence in lanthanum manganite thin films under variation of oxygen content
XPS investigation of Mn valence in lanthanum manganite thin films under variation of oxygen content
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DOI：
10.1103/physrevb.73.155425
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发表时间：
2006-04-01
影响因子：
3.7
通讯作者：
Dörr, K
中科院分区：
文献类型：
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作者：
Beyreuther, E;Grafström, S;Dörr, K
到目前为止，关于LaMnO₃是否能接受诸如铈等四价阳离子的掺杂，从而能够制备电子掺杂的混合价态镧锰氧化物这一问题一直存在争议。在此问题的背景下，我们对外延的La₀.₇Ce₀.₃MnO₃（LCeMO）和La₀.₇Ca₀.₃MnO₃（LCMO）薄膜进行了一项比较性的X射线光电子能谱（XPS）研究。我们重点关注了Mn 3s芯能级峰的交换分裂，它是Mn价态的直接指标，使我们能够对薄膜最外层3nm内的Mn价态进行量化。我们证明，根据氧含量的不同，在LCeMO和LCMO薄膜中，Mn价态都可以在混合的Mn³⁺/⁴⁺态和混合的Mn²⁺/³⁺态之间进行调节。通过在超高真空中加热进行脱氧以及在氧气气氛中加热进行再氧化来改变氧含量。在LCeMO薄膜中，脱氧不仅改变了Mn价态，而且还使Ce价态从⁴⁺态向³⁺态转变。
The question whether LaMnO3 accepts doping with tetravalent cations such as cerium and thus allows the preparation of electron-doped mixed-valent lanthanum manganites has been discussed controversially so far. Against the background of this problem, we present a comparative x-ray photoemission (XPS) study of epitaxial La0.7Ce0.3MnO3 (LCeMO) and La0.7Ca0.3MnO3 (LCMO) thin films. We focus on the exchange splitting of the Mn 3s core level peak, which is a direct indicator of the Mn valence and allows us to quantify the Mn valence in the outermost 3 nm of the films. We demonstrate that, depending on the oxygen content, the Mn valence can be tuned between a mixed Mn3+/4+ state and a mixed Mn2+/3+ state in both the LCeMO and the LCMO film. The oxygen content was varied by heating in ultrahigh vacuum for deoxygenation and in an oxygen atmosphere for reoxidation. In the LCeMO film, the deoxygenation not only changes the Mn valence, but also the Ce valence is driven from the 4+ towards the 3+ state.