【摘要】 本文通过高分辨电子能量损失谱(EELS)的实验分析与密度泛函计算相结合的方法,研究了NaxCoO2.yH2O系统的电子结构特性和电子关联效应。实验结果表明,金属性Na0.3CoO2材料和电荷有序绝缘体Na0.5CoO2的O-K吸收边存在明显的结构差别,在Na0.5CoO2的EELS中第一个峰发生明显分裂,密度泛函计算证实这种分裂现象和电子关联效应直接相关。通过理论模拟谱线与实验谱线的比较确定了其电子关联强度为U=3.0 eV。在Na0.3CoO2.yH2O(y=0,0.6,1.3)超导体系中,实验发现其能损谱的低能部分随着水含量的增加发生系统的变化,损失峰向低能量方向逐步移动。电子结构计算表明水分子的插入可以引起费米面附近能态原子轨道杂化情况的改变,从而导致EELS的变化。更多还原

【Abstract】 The electronic structures and electron correlation effects in Na_xCoO₂·yH₂O system have been investigated by combining the measurements of electron energy-loss spectroscopy（EELS） and density functional theory（DFT） calculations. The experimental data of the O-K edge in Na_0.5CoO₂,in contrast with that of Na_0.3CoO₂,shows distinct splitting in the first peak.The DFT calculations demonstrate that this kind of peak split is caused by the presence of significant electron correlation in Na_0.5CoO₂,the electron correlation strength is determined to be about 3 eV.Measurements of the low-loss spectra in Na_0.3CoO₂,Na_0.3CoO₂·0.6H₂O and Na_0.3CoO₂·1.3H₂O reveal that the peak position shifts towards the low energy direction systematically with increasing water intercalation.The DFT calculations suggest that the water intercalation could lead to changes in the orbital composition for the states near the Fermi level,which results in notable alternations of EELS structures and shifts of peak positions.更多还原