[论文解读] Oxygen vacancy induced room temperature metal-insulator transition in nickelates films and its potential application in photovoltaics

Le Wang, Sibashisa Dash+11 more|arXiv (Cornell University)|Feb 10, 2016

Magnetic and transport properties of perovskites and related materials参考文献 7被引用 5

一句话总结

本研究在室温下通过氧空位诱导实现了外延NdNiO3薄膜的可逆金属-绝缘体转变，方法为低温后退火。该方法实现了超过六数量级的电阻调制和可调谐的光学带隙变化，氧空位稳定了绝缘相，增强了磁化强度，并使异质结中的光伏应用成为可能。

ABSTRACT

Oxygen vacancy is intrinsically coupled with magnetic, electronic and transport properties of transition-metal oxide materials and directly determines their multifunctionality. Here, we demonstrate reversible control of oxygen content by post-annealing at temperature lower than 300 degree centigrade and realize the reversible metal-insulator transition in epitaxial NdNiO3 films. Importantly, over six orders of magnitude in the resistance modulation and a large change in optical band gap are demonstrated at room temperature without destroying the parent framework and changing the p-type conductive mechanism. Further study revealed that oxygen vacancies stabilized the insulating phase at room temperature is universal for perovskite nickelates films. Acting as electron donors, oxygen vacancies not only stabilize the insulating phase at room temperature, but also induce a large magnetization of ~50 emu/cm3 due to the formation of strongly correlated Ni2+ t2g6eg2 states. The band gap opening is an order of magnitude larger than that of the thermally driven metal-insulator transition and continuously tunable. Potential application of the newly found insulating phase in photovoltaics has been demonstrated in the nickelates-based heterojunctions. Our discovery opens up new possibilities for strongly correlated perovskite nickelates.

研究动机与目标

• 在不引起结构退化的情况下，实现室温下镍酸盐薄膜的可逆金属-绝缘体转变。
• 研究氧空位在稳定绝缘相及调控电子和光学性质中的作用。
• 探索氧空位工程修饰的镍酸盐在光伏异质结器件中的潜力。
• 理解氧空位浓度、电子结构与钙钛矿型镍酸盐磁性之间的关联。

提出的方法

• 在低于300 °C的温度下对外延NdNiO3薄膜进行后退火，以控制氧空位浓度。
• 采用原位和非原位表征技术监测氧含量及电子转变行为。
• 测量电阻率和光学带隙随氧空位浓度的变化。
• 分析磁性性质，以关联氧空位引起的电子态变化。
• 制备并测试镍酸盐基异质结，评估其光伏性能。
• 对氧空位引起的电子掺杂形成的Ni2+ t2g⁶eg²态进行理论建模。

实验结果

研究问题

• RQ1 氧空位是否能在室温下诱导NdNiO3薄膜的可逆金属-绝缘体转变？
• RQ2 氧空位浓度如何影响外延镍酸盐薄膜的电阻率和光学带隙？
• RQ3 氧空位在稳定绝缘相和增强磁化强度方面起什么作用？
• RQ4 能否将氧空位工程修饰的绝缘相应用于光伏异质结？
• RQ5 氧空位诱导的绝缘相中带隙打开是否显著大于热驱动转变中的带隙？

主要发现

• 通过控制氧空位，实现了室温下超过六数量级的电阻调制。
• 观察到光学带隙的大幅且连续可调变化，其变化幅度比热驱动转变高出一个数量级。
• 氧空位在室温下稳定了绝缘相，并诱导出约50 emu/cm³的磁化强度。
• 绝缘相由氧空位引起的电子掺杂稳定，形成强关联的Ni2+ t2g⁶eg²态。
• 氧空位诱导的绝缘相在异质结器件中实现了高效的光伏响应。
• 母体钙钛矿结构保持完整，尽管发生转变，仍保留了p型导电机制。