Study on local structure of silicate perovskites by NMR spectroscopy

结果总结如下。核磁共振谱仪的设置：我所引进了一台400 MHz固体MAS核磁共振谱仪。现在，对^<29>Si、^<27>Al、^<23>Na、^1H等的MAS NMR的常规测量是可能的。2001年推出的新探针使我们能够研究低频核，如<25>Mg，并进行多量子NMR实验。该仪器现已向外部研究人员开放，供其开展合作研究项目。化学位移的从头计算：利用分子轨道技术，我们计算了与熔体或玻璃结构相关的各种硅酸盐团簇。计算的位移很好地再现了观察到的化学位移。为了更好地对NMR谱进行归属，我们还计算了实验上没有很好表征的局域结构，如Al三簇.电场梯度（EFG）的第一性原理计算：为了预测四极核（如矿物中的Al）的EFG，已经进行了第一性原理计算。预测了Ca_2Al_2O_5氧缺陷钙钛矿中的大EFG。例如。4.水合玻璃的结构：为了研究水和硅酸盐熔体的相互作用，我们使用^<29>Si和^1H MAS NMR和^1H-^<29>Si CP MAS NMR研究了水合熔体。结果表明，水的存在导致熔体结构的畸变。这与通常的观察相反，是非常重要的发现。含硫玻璃的结构：为了了解硫如何溶解在硅酸盐熔体中，用13 Si MAS NMR研究了含硫玻璃<29>。当硫以自然硫的形式加入时，熔体结构发生聚合.矿物的水化作用：利用^ Si和^1H MAS NMR研究了镁橄榄石、顽火辉石和透辉石的水化过程<29>。我们观察到聚合在水化层在所有系统的研究。水-硅酸盐相互作用的晶体化学：从这些研究中，我们对水和硅酸盐之间的相互作用有了更好的晶体化学认识。

The results are summarized below.1. Setup of NMR spectrometer: We have introduced a 400MHz solid MAS NMR spectrometer to our institute. Now routine measurements of MAS NMR for ^<29>Si, ^<27>Al, ^<23>Na, ^1H etc are possible. New probe introduced in 2001 allows us to study low frequency nuclei such as ^<25>Mg, and to conduct multi-quantum NMR experiments. The instrument is now open to external researchers for cooperative research projects.2. Ab initio calculation of chemical shifts: Using molecular orbital technique, we have calculated wide varieties of silicate clusters relevant to melt or glass structures. Calculated shifts well reproduced observed chemical shifts. In order to better assignments of NMR spectra, we also calculated experimentally not-well characterized local structures, such as Al triclusters.3. First-principles calculation of electric field gradient (EFG): In order to predict EFG at quadrupolar nuclei such as Al in minerals, first-principles calculations have been conducted. Large EFG in Ca_2Al_2O_5 oxygen-defected perovskite was predicted. For example.4. Structure of hydrous glasses: In order to investigate water and silicate melt interaction, we have studied hydrous melts using ^<29>Si and ^1H MAS NMR and ^1H-^<29>Si CP MAS NMR. The result shows that water causes melt structure polymerize. This is contrary to common observation, and is very important discovery.5. Structure of sulfur-bearing glasses: In order to see how sulfur dissolves in silicate melts, S-bearing glasses were studied by ^<29>Si MAS NMR. When sulfur is added as native S, melt structure was polymerized.6. Hydration of minerals: Hydration processes of forsterite, enstatite and diopside have studied using ^<29>Si and ^1H MAS NMR. We observed polymerization in hydration layer in all systems studied.7. Crystal chemistry of water-silicate interaction: From these studies, we have gained better crystal chemical insights of the interaction between water and silicate.