Siegel Renée, Hirschinger Jérôme, Carlier Dany, Ménétrier Michel, Delmas Claude
Institut de Chimie, FRE 2446 CNRS, Université Louis Pasteur, BP 296, Strasbourg Cedex 67008, France.
Solid State Nucl Magn Reson. 2003 Jun;23(4):243-62. doi: 10.1016/S0926-2040(03)00017-1.
59Co and 23Na NMR has been applied to the layered cobalt oxides NaCoO(2) and HCoO(2) at three different magnetic field strengths (4.7, 7.1 and 11.7T). The 59Co and 23Na quadrupole and anisotropic shift tensors have been determined by iterative fitting of the NMR line shapes at the three magnetic field strengths. Due to the large 59Co quadrupole interaction in NaCoO(2), a frequency-swept irradiation procedure was used to alleviate the limited bandwidth of the excitation. While the 59Co and 23Na shift and quadrupole coupling tensors in NaCoO(2) are found to be coincident and axially symmetric in agreement with the crystal symmetry requirements, the fits of the 59Co NMR spectra clearly show the presence of structural disorder in HCoO(2). The 23Na chemical shift anisotropy can be reproduced by shift tensor calculations using a point dipole model and considering that the magnetic susceptibility in NaCoO(2) is due to Van Vleck paramagnetism for Co(3+). Electric field gradient calculations using either the empirical point charge model or the ab initio full potential-linearized augmented plane wave method are compared with the experimental NMR data.
59Co和23Na核磁共振已应用于层状钴氧化物NaCoO₂和HCoO₂，测量磁场强度为三个不同值（4.7、7.1和11.7T）。通过对三个磁场强度下的核磁共振线形进行迭代拟合，确定了59Co和23Na的四极矩张量和各向异性位移张量。由于NaCoO₂中59Co的四极相互作用较大，采用了频率扫描辐照程序来缓解激发带宽的限制。虽然发现NaCoO₂中59Co和23Na的位移张量和四极耦合张量与晶体对称性要求一致，呈轴向对称，但59Co核磁共振谱的拟合结果清楚地表明HCoO₂中存在结构无序。利用点偶极子模型并考虑到NaCoO₂中的磁化率是由Co(3+)的范弗莱克顺磁性引起的，通过位移张量计算可以再现23Na化学位移各向异性。将使用经验点电荷模型或从头算全势线性缀加平面波方法进行的电场梯度计算与实验核磁共振数据进行了比较。
