Aramburu José Antonio, García-Fernández Pablo, García-Lastra Juan María, Moreno Miguel
Departamento de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Avenida de los Castros s/n, 39005, Santander, Spain.
Center for Atomic-Scale Materials Design, Department of Physics, Technical University of Denmark, DK-2800, Kongens Lyngby, Denmark.
Chemphyschem. 2016 Jul 18;17(14):2146-56. doi: 10.1002/cphc.201600206. Epub 2016 Apr 18.
First-principle calculations together with analysis of the experimental data found for 3d(9) and 3d(7) ions in cubic oxides proved that the center found in irradiated CaO:Ni(2+) corresponds to Ni(+) under a static Jahn-Teller effect displaying a compressed equilibrium geometry. It was also shown that the anomalous positive g∥ shift (g∥ -g0 =0.065) measured at T=20 K obeys the superposition of the |3 z(2) -r(2) ⟩ and |x(2) -y(2) ⟩ states driven by quantum effects associated with the zero-point motion, a mechanism first put forward by O'Brien for static Jahn-Teller systems and later extended by Ham to the dynamic Jahn-Teller case. To our knowledge, this is the first genuine Jahn-Teller system (i.e. in which exact degeneracy exists at the high-symmetry configuration) exhibiting a compressed equilibrium geometry for which large quantum effects allow experimental observation of the effect predicted by O'Brien. Analysis of the calculated energy barriers for different Jahn-Teller systems allowed us to explain the origin of the compressed geometry observed for CaO:Ni(+) .
第一性原理计算以及对立方氧化物中3d(9)和3d(7)离子的实验数据的分析表明，在辐照的CaO:Ni(2+)中发现的中心对应于处于静态 Jahn-Teller 效应下的Ni(+)，呈现出压缩的平衡几何结构。研究还表明，在T = 20 K时测量到的异常正g∥位移（g∥ - g0 = 0.065）服从由与零点运动相关的量子效应驱动的|3 z(2) - r(2) ⟩和|x(2) - y(2) ⟩态的叠加，这是一种由奥布赖恩首先针对静态 Jahn-Teller 系统提出，后来由哈姆扩展到动态 Jahn-Teller 情况的机制。据我们所知，这是第一个真正的 Jahn-Teller 系统（即在高对称构型下存在精确简并的系统），其呈现出压缩的平衡几何结构，并且大的量子效应使得能够通过实验观察到奥布赖恩所预测的效应。对不同 Jahn-Teller 系统计算出的能垒的分析使我们能够解释在CaO:Ni(+)中观察到的压缩几何结构的起源。
