Kyoto University · 공학
Keiji Shimoda 교수의 연구실은 주로 고체 상태 핵자기 공명(NMR) 및 분자 동역학 시뮬레이션을 활용해 금속 산화물 및 유리 상태 물질의 국소 구조를 정밀하게 분석합니다. 특히 마그네슘 이온의 배위 환경, 다이벌런트 카이온의 구조적 기여, 리튬 이온 배터리 및 철광석 슬래그의 상전이 거동에 대한 기초 연구를 중심으로 하고 있습니다. 고해상도 NMR 기법을 통해 기존에 알려지지 않은 다수의 Mg 이온 서브스펙트럼과 다이아몬드형 구조의 산화물 네트워크를 규명하며, 재료의 거시적 성질을 이해하는 데 기여하고 있습니다.
표시된 성과는 수집된 데이터 기준으로 산출되며, 일부 차이가 있을 수 있습니다.
Structural information on divalent cations such as Mg2+ should have important implications for magmatic liquids because of their abundance in the Earth.s interior; nevertheless, little is confirmed about their coordination environments. We here apply a 25Mg triple-quantum magic-angle spinning (3QMAS) NMR technique at an ultra-high magnetic field (21.8 T) and successfully show the occurrence of multiple Mg sites in MgSiO3 glass. We find that these sites are distinguished by the degree of polyhedr
The layered-to-spinel phase transformation in Li<sub>2</sub>MnO<sub>3</sub> during the initial charge process occurs by a two-phase reaction process within a single particle.
The chemical structure of an amorphous slag with blast furnace composition was investigated by means of molecular dynamics simulation. Our calculation suggested that the slag had a depolymerized network of SiO4 and AlO4 tetrahedra with interstitial cations, Ca2+ and Mg2+. The structural properties such as average coordination number obtained at 300 K were in good agreement with a recent NMR study, supporting the feasibility of the structure prediction by such simulation technique. At 1 873 K, th
We have reported the 25Mg triple-quantum magic-angle spinning (3QMAS) NMR spectra of silicate glasses. The two-dimensional spectra suggest that the magnesium ions in MgSiO3, CaMgSi2O6, Ca2MgSi2O7, Mg3Al2Si3O12, and Li2MgSi2O6 glasses are mainly in octahedral environments, although in Na2MgSi2O6, K2MgSi2O6, and K2MgSi5O12 glasses they form tetrahedral species. We discussed the coordination environments of Mg based on the field strength of competing Mg2+, Ca2+, Na+, K+, and Li+ cations, and convin
The thermal decomposition pathways of ammonia borane (AB, NH3BH3), lithium amidoborane (LiAB, LiNH2BH3), and potassium amidoborane (KAB, KNH2BH3) have been investigated in detail by using solid state 11B MAS NMR spectroscopy. During the first decomposition process of AB, the complex structural entities were observed, which have been attributed to polyaminoborane (PAB, (NH2BH2)n). On the other hand, polyiminoborane (PIB, (NHBH)n) formed in the second process showed a single 3-fold coordination II
The oxidation/reduction behaviours of lattice oxygen and transition metals in Li[Li<sub>0.25</sub>Ni<sub>0.20</sub>Mn<sub>0.55</sub>]O<sub>1.93</sub>are investigated by using HAX-PES.
The thermal decomposition pathway of sodium amidoborane (NaAB; NaNH2BH3) has been investigated in detail by using solid state NMR spectroscopy. 23Na MAS/3QMAS NMR spectra suggested that NaH and an amorphous Na–N–B–H phase started to be formed as decomposition products even at 79 °C, although NaAB was prepared from NaH and NH3BH3 by ball milling at room temperature. Based on the quantitative analyses of the 23Na MAS spectra, we proposed a decomposition reaction to 200 °C to be NaNH2BH3 → Na0.5NBH
The pressure-induced structural evolutions of CaSiO(3)-MgSiO(3) glasses have been examined by means of molecular dynamics simulation. Our calculations revealed that Si coordination remained unchanged up to 15 GPa, while modifier cations caused significant changes in the short-range order structure. In the present study, we conclude that the main compression mechanisms for CaSiO(3)-MgSiO(3) glasses are: (1) the Si-O-Si angle reduction, (2) the coordination increase of Ca and Mg cations, and (3) t
Delithiation and lithiation behaviors of ordered spinel LiNi0.5Mn1.5O4 and disordered spinel LiNi0.4Mn1.6O4 were investigated by using in situ (in operando) 7Li NMR and ex situ 6Li MAS NMR spectroscopy. The in situ 7Li monitoring of the ordered spinel revealed a clear appearance and subsequent disappearance of a new signal from the well-defined phase Li0.5Ni0.5Mn1.5O4, suggesting the two-phase reaction processes among Li1.0Ni0.5Mn1.5O4, Li0.5Ni0.5Mn1.5O4, and Li0.0Ni0.5Mn1.5O4. Also, for the dis
Fluoride-ion batteries (FIBs), which use F– ion migration to drive charge–discharge cycles, have recently gained academic attention as the next generation of rechargeable batteries. Copper difluoride (CuF2) represents a promising positive electrode material for FIBs owing to its high theoretical capacity and high redox potential. In this study, the high-temperature electrochemical reversibility of a CuF2 composite electrode in a bulk-type all-solid-state FIB is evaluated. The CuF2 composite elec
