岡山大学惑星物質研究所
固体ＮＭＲ研究室

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• マントル無水及び含水鉱物における水

  Water is the most important volatile component that may significantly affect the thermodynamic and physical properties of minerals even at trace level, and thus knowledge about how and how much water is incorporated into mantle minerals is indispensable in order to understand the structure and dynamics of Earth and planetary interiors, and how they are related to the planetary habitability. Despite extensive studies, the current understanding on these issues are limited (and often wrong) due to difficulties of interpreting data of more commonly used spectroscopic techniques, such as infrared spectroscopy.
  
  We take a unique, comprehensive approach of combining multi-nuclear, multi-dimensional NMR, vibrational spectroscopy and first-principles calculation, which allows us to gain an unambiguous understanding of these issues. We have carried out extensive work over the years on diverse hydrous mantle minerals (and silicate glasses) synthesized using high P-T apparatus, which provided us with deep insights in the behavior of water in Earth materials and the expertise to study them even at trace levels (see publication list). Our recent work on the more challenging nominally anhydrous minerals, including the most abundant upper mantle minerals, olivine (Xue et al., 2017, Am Mineral) and pyroxene (Xue et al. 2024 Contrib Mineral Petrol; Xue et al., in prep), demonstrated the power of this approach. It allowed us to unambiguously clarify how water is incorporated in these mantle minerals, and also revealed that the commonly used infrared spectroscopic technique failed to detect part of the incorporated OH defects in orthoenstatite (pyroxene) that have strong hydrogen bonding, and thus underestimated the water solubility. This finding has implications well beyond pyroxene, and may change our common sense about how much water may be stored in the deep planetary interiors. The goal of our ongoing project is to extend the approach to all major mantle minerals, especially the most important lower mantle mineral, bridgmanite.
  
  It is expected that our understanding about how water is present in the deep Earth and other planets may be significantly advanced in the coming years with the progress of this exciting and ambitious ongoing project.
  
  

• 鉱物及び関連無機物質のNMR結晶学（NMR crystallography）

  The rich variety of structural information that may be provided by multi-nuclear, multi-dimensional NMR can be combined with powder X-ray diffraction (NMR crystallography) for structural determination of minerals and related materials with complicated crystal structure that may be difficult to solve with other means. Together with Prof. Masami Kanzaki, we have used this approach and successfully determined the crystal structures of a number of high-pressure phases synthesized in the lab, that were either discovered by us (e.g. three AlPO4 phases: Kanzaki et al., 2011; Kanzaki and Xue, 2012), or reported by others long time ago, but with structures remaining unsolved (e.g. two Zn2SiO4 phases: Liu et al., 2013; two oxygen-deficient perovskite phases in the CaSiO3-CaAlO2.5 join: Kanzaki et al., 2017).
  
  

• 天然鉱物におけるカチオンの秩序・無秩序及び水素結合

  Cation order/disorder (e.g. Al/Si) and hydrogen bonding are two important factors controlling the thermodynamic and physical properties of minerals. NMR has long been regarded as a powerful tool in providing such information, for which X-ray diffraction tends to be insensitive. Traditionally, the interpretation of NMR spectra relies on empirical knowledge about the correlation between NMR parameters and local structural parameters, which tend to be ambiguous. The approach we adopted in combining multi-nuclear, multi-dimensional NMR with first-principles calculation has revolutionized the situation, and allowed us to gain detailed, unambiguous picture. A good example is our recent work on the natural mineral, ussingite (Na2AlSi3O8OH) (Xue and Kanzaki, 2024). We were able to completely clarify the nature of Si-Al disorder and how it affects the next-nearest neighbor environments of Si/Al and H, with the experimental NMR data in complete agreement with first-principles calculation results, providing a 3D view of the disordered local structure. Our study also revealed an intriguing correlation between the Si-Al disorder and the hydrogen bonding distance variation, which may be a universal phenomenon applicable also to other hydrous minerals.
  
  

• 珪酸塩メルト（ガラス）の構造

  We also did extensive work over the years on the structure of silicate melts (glasses). In particular, our series of work on hydrous (alumino)silicate melts with different degrees of polymerization and cation types clarified how the water incorporation mechanisms change as a function of melt composition, and provided the basis for understanding the behavior of natural magma of different compositions.
  Xue and Kanzaki (2009, J Am Ceramic Soc, feature article) provided a good review of our work up to then.
  
  

• NMRの幅広い地球惑星物質及び関連物質への応用

  It is our goal that the power of NMR spectroscopic technique is fully utilized to help solve diverse structural issues on Earth and planetary materials and related materials. Toward that goal, we welcome collaboration with researchers both in Japan and worldwide (including students and young researchers). Some examples of past and ongoing collaborative projects include calcite minerals (with Prof. Hiroyuki Kagi, Tokyo Univ), CaTiO3-CaAl2O5 defect perovskite (with Prof. Takuya Nagai, Hokaido Univ), natural zeolite, garnet and synthetic hydrogarnet minerals (with Prof. Charles Geiger, Austria), natural and synthetic prehnite minerals (with Prof. Jonathan Stebbins, Stanford Univ).
  
  If you have a project that may benefit from NMR measurements, do not hesitate to contact Xue for potential collaboration. Travel and accommodation fees may be provided via IPM's joint-use/joint research program. It is also possible to send the samples for us to do the analyses.
  
  

大学院生・共同研究者の募集

• 当研究所は大学院生（修士、博士課程）を募集しています。
  分光法測定、第一原理計算、高圧実験などによる地球物質の構造物性研究に興味のある方はお問い合わせ・見学して下さい。優れた学生には、経済支援もあります。
  
  
• 共同研究者も募集しています。
  先端固体ＮＭＲ分光法や、顕微ラマン分光法などを使って、地球物質及び関連材料の構造を解明したい方はお問い合わせ下さい。学生や若い研究者は特に歓迎します。必要な教育指導も行えます。本研究所の共同利用・共同研究拠点プログラムにより、旅費・滞在費の支援も可能です。また、依頼分析も対応できます。
  
  

最近の論文(2016-現在)