Pengcheng Hu, Binxiang Huang, Daniel Bremecker, Jurij Koruza, Karsten Albe, Andreas Klein
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引用次数: 0
摘要
研究了未掺杂和掺锌的 0.94Na1/2Bi1/2TiO3-0.06BaTiO3 无铅压电陶瓷(NBT-6BT)的(电)化学稳定性。为此,通过在真空中退火或在 Pt/NBT-6BT/ITO 上施加电压来逐渐还原 ITO 薄膜,从而改变 NBT-6BT 和掺杂锡的 In2O3(ITO)电极之间界面的费米级。化学和电子变化通过 X 射线光电子能谱进行现场监测。实验表明,当费米级达到价带最大值以上 2.23 ± 0.10 eV 时,就会形成金属铋,而钛则不会被还原。Bi 的电化学还原构成了费米级的上限,即低于导带最小值 ≈1 eV。因此,NBT-6BT 的导电性可以排除导带中电子浓度过高和自由电子的影响。当 ITO 的功函数为 4.2-4.3 eV 时,导电率会降低。由于 Ag、Cu、Ni 或 Pt 等典型电极材料具有更高的功函数,因此预计陶瓷电容器的电极界面不会出现电化学不稳定现象。在给定的实验条件下(350 °C,电场<40 V/mm),没有观察到电阻下降和界面上 Na 的富集。
Fermi level limitation in Na1/2Bi1/2TiO3–BaTiO3 piezoceramics by electrochemical reduction of Bi
The (electro)chemical stability of undoped and Zn-doped 0.94Na1/2Bi1/2TiO3–0.06BaTiO3 lead-free piezoceramics (NBT–6BT) was studied. For this purpose, the Fermi level at the interface between NBT–6BT and Sn-doped In2O3 (ITO) electrode is varied by gradually reducing the ITO film either by annealing in vacuum or by applying a voltage across a Pt/NBT–6BT/ITO. The chemical and electronic changes are monitored in situ by x-ray photoelectron spectroscopy. The experiments reveal the formation of metallic Bi when the Fermi level is reaching a value of 2.23 ± 0.10 eV above the valence band maximum, while no reduction of Ti is observed. The electrochemical reduction of Bi constitutes an upper limit of the Fermi level at ≈1 eV below the conduction band minimum. High electron concentrations in the conduction band and a contribution of free electrons to the electrical conductivity of NBT–6BT can, therefore, be excluded. The reduction occurs for an ITO work function of 4.2–4.3 eV. As typical electrode materials such as Ag, Cu, Ni, or Pt have higher work functions, an electrochemical instability of the electrode interfaces in ceramic capacitors is not expected. Under the given experimental conditions (350 °C, electric fields <40 V/mm), no degradation of resistance and no enrichment of Na at the interface are observed.
期刊介绍:
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