Bräuniger Thomas, Groh Burkhard, Moudrakovski Igor L, Indris Sylvio
Department of Chemistry, University of Munich (LMU) Butenandtstr. 5-13, 81377 Munich, Germany.
Max-Planck-Institute for Solid-State Research , Heisenbergstr. 1, 70569 Stuttgart, Germany.
J Phys Chem A. 2016 Oct 13;120(40):7839-7846. doi: 10.1021/acs.jpca.6b07286. Epub 2016 Sep 29.
From single-crystal Al NMR experiments, the full tensors for both the electrical field gradient (EFG) and the chemical shift (CS) for the aluminum atoms in γ-LiAlO have been determined. A simultaneous fit of the quadrupolar splittings observed for the four Al in the unit cell gave the EFG tensor in the crystal frame, from which a quadrupolar coupling constant of χ = C = 3.330 ± 0.005 MHz and an asymmetry parameter of η = 0.656 ± 0.002 were derived. The experimentally determined quadrupolar splittings were sufficiently sensitive to quantify small deviations of both rotation axis direction and starting direction by the data fitting routine. For determination of the CS tensor, the evolution of the outer satellite centers over the crystal rotation was tracked, and the contribution of the quadrupolar shift was subtracted according to the previously determined EFG tensor. The resulting CS tensor of Al yields an isotropic chemical shift of δ = 81.8 ± 0.25 ppm and an asymmetry parameter of η = 0.532 ± 0.004, in good agreement with the fit of a MAS NMR spectrum acquired at B = 21.1 T. From both experiments and DFT calculations using the Castep code, we find the eigenvectors of the EFG and CS tensors to be practically colinear.
通过单晶铝核磁共振实验，已确定了γ-LiAlO中铝原子的电场梯度（EFG）和化学位移（CS）的完整张量。对晶胞中四个铝原子观测到的四极分裂进行同时拟合，得到了晶体坐标系中的EFG张量，由此推导出四极耦合常数χ = C = 3.330 ± 0.005 MHz和不对称参数η = 0.656 ± 0.002。实验测定的四极分裂对通过数据拟合程序量化旋转轴方向和起始方向的小偏差足够敏感。为了确定CS张量，追踪了晶体旋转过程中外卫星中心的演化，并根据先前确定的EFG张量减去了四极位移的贡献。所得铝的CS张量给出了各向同性化学位移δ = 81.8 ± 0.25 ppm和不对称参数η = 0.532 ± 0.004，与在B = 21.1 T下采集的MAS NMR谱的拟合结果吻合良好。通过实验和使用Castep代码的DFT计算，我们发现EFG和CS张量的特征向量几乎共线。
