Crystal Growth Centre, Anna University, Chennai 600 025, India.
J Phys Chem B. 2010 Feb 11;114(5):1775-81. doi: 10.1021/jp907469n.
(27)Al solid-state NMR has been employed to study the perturbations to (27)Al electric field gradients for the aluminum environments in nanocrystalline alpha-alumina. Triple quantum magic angle spinning experiments show that the octahedral aluminum coordination remains unchanged down to 12 nm, although severe perturbations to (27)Al electric field gradients are noticed at 28 nm and below. 3Q-MAS and SATRAS experimental data of nano alpha-alumina have been analyzed through extensive spectral simulations to probe (27)Al electric field gradients of aluminum in the grains and grain boundaries. While the aluminum in the grains has a unique field gradient tensor, the same octahedrally coordinated aluminum environments in the grain boundaries suffer a distribution of electric field gradients. This is evidenced by data analysis of both 3Q-MAS and SATRAS spectra. By invoking the Gaussian isotropic model, in which the (C(Q), eta(Q)) parameter space is discretely sampled by the Czjzek distribution, we have been able to analyze the (27)Al SATRAS spectra of nanocrystalline alpha-alumina samples having grain sizes of 52, 28, 20, and 12 nm. Good agreement between experimental and simulated spectra has led to the quantitative determination of grain and grain boundary components in these materials.
（27）固态 NMR 已被用于研究纳米晶α-氧化铝中铝环境的（27）Al 电场梯度的扰动。三量子魔角旋转实验表明，八面体铝配位数在 12nm 以下保持不变，尽管在 28nm 及以下会观察到（27）Al 电场梯度的严重扰动。通过广泛的光谱模拟，对纳米α-氧化铝的 3Q-MAS 和 SATRAS 实验数据进行了分析，以探测晶粒和晶界中铝的（27）Al 电场梯度。虽然晶粒中的铝具有独特的电场梯度张量，但晶界中同样的八面体配位的铝环境会受到电场梯度分布的影响。这一点可以通过对 3Q-MAS 和 SATRAS 光谱的数据分析得到证明。通过调用高斯各向同性模型，其中（C(Q)，eta(Q)）参数空间由 Czjzek 分布离散采样，我们已经能够分析具有晶粒尺寸为 52、28、20 和 12nm 的纳米晶α-氧化铝样品的（27）Al SATRAS 光谱。实验和模拟光谱之间的良好一致性导致了这些材料中晶粒和晶界成分的定量确定。
