New Chemistry Unit, International Centre for Materials Science, CSIR Centre of Excellence in Chemistry, Sheikh Saqr Laboratory, Jawaharlal Nehru Centre for Advanced Scientific Research , Jakkur, Bangalore-560064, India.
Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research , Jakkur, Bangalore-560064, India.
J Am Chem Soc. 2016 Jul 6;138(26):8228-34. doi: 10.1021/jacs.6b04198. Epub 2016 Jun 24.
Substitution of aliovalent N(3-) and F(-) anions in place of O(2-) in ZnO brings about major changes in the electronic structure and properties, the composition, even with 10 atomic percent or less of the two anions, rendering the material yellow colored with a much smaller band gap. We have examined the variation of band gap of ZnO with progressive substitution of N and F and more importantly prepared Zn2NF which is the composition one obtains ultimately upon complete replacement of O(2-) ions. In this article, we present the results of a first complete study of the crystal and electronic structures as well as of properties of a stable metal nitride fluoride, Zn2NF. This material occurs in two crystal forms, tetragonal and orthorhombic, both with a band gap much smaller than that of ZnO. Electronic structures of Zn2NF as well as ZnO0.2N0.5F0.3 investigated by first-principles calculations show that the valence bands of these are dominated by the N (2p) states lying at the top. Interestingly, the latter is a p-type material, a property that has been anticipated for long time. The calculations predict conduction and valence band edges in Zn2NF to be favorable for water splitting. Zn2NF does indeed exhibit good visible-light-induced hydrogen evolution activity unlike ZnO. The present study demonstrates how aliovalent anion substitution can be employed for tuning band gaps of materials.
在 ZnO 中，不等价的 N(3-)和 F(-)阴离子取代 O(2-)会导致电子结构和性质发生重大变化，即使组成中只有 10%或更少的两种阴离子，也会使材料呈现黄色，带隙更小。我们研究了 ZnO 带隙随 N 和 F 逐渐取代的变化，更重要的是制备了 Zn2NF，这是 O(2-)离子完全取代后最终得到的组成。在本文中，我们首次全面研究了稳定的金属氮氟化物 Zn2NF 的晶体和电子结构以及性质。这种材料有两种晶体形式，四方和正交，它们的带隙都比 ZnO 小得多。通过第一性原理计算研究了 Zn2NF 和 ZnO0.2N0.5F0.3 的电子结构，结果表明这些材料的价带主要由顶部的 N(2p)态主导。有趣的是，后者是一种 p 型材料，这一性质早已有预期。计算预测 Zn2NF 的导带和价带边缘有利于水分解。Zn2NF 确实表现出良好的可见光诱导析氢活性，这与 ZnO 不同。本研究表明，不等价阴离子取代可以用于调整材料的带隙。
