Sung Keun Lee

Synthetic epidotes were produced using a Tuttle type hydrothermal vessel in the temperature range from 500 to 700 ℃ and at 4.5 to 5.0 kbars pressure. Single-crystal X-ray diffraction structure refinements yielded intracrystalline cation distributions for two crystals grown at 600 ℃ (0.68 and 0.73 Fe apfu) and five crystals grown at 700 ℃ (0.88 to 1.08 Fe apfu). The resulting Fe occupancies were compared with those calculated according to a thermodynamic model: The samples formed at 700 ℃ display

We investigate short-range order and local atomic configuration in charge-balanced aluminosilicate glasses as functions of composition, using 17O and 27Al MAS and triple-quantum magic angle spinning (3QMAS) NMR spectroscopy. Enhanced resolution in 17O and 27Al 3QMAS spectra, compared to MAS NMR, allows the quantification of the spectra and the extent of disorder using a semiempirical function relating 3QMAS efficiency to a quadrupolar coupling constant (Cq). The variations with the Si/Al ratio (

Whereas prototypical Al(2)O(3) is not a glass former, amorphous Al(2)O(3) can be formed as thin films through vapor deposition and can serve as a structural model for the Al(2)O(3) glass. The first two-dimensional solid-state NMR experiments for amorphous Al(2)O(3) thin film reveal that four- and five-coordinated species are predominant (95%), while six-coordinated species are minor. Such a species distribution is remarkably similar to what has been predicted theoretically for Al(2)O(3) melts. U

Soda-lime silicate glass is the fundamental base glass for many technologically important oxide glasses, and it has been used as window glass since the Roman Empire. Mixed-cation silicates also are useful models of the structure and dynamics of basaltic magmas and mantle melts. The diffusivity of Na+ in silicate melts and its variation with composition play key roles in melting behavior. This property also depends strongly on the composition and framework structures of glasses and melts and on t

Silicate melts at the top of the transition zone and the core-mantle boundary have significant influences on the dynamics and properties of Earth's interior. MgSiO3-rich silicate melts were among the primary components of the magma ocean and thus played essential roles in the chemical differentiation of the early Earth. Diverse macroscopic properties of silicate melts in Earth's interior, such as density, viscosity, and crystal-melt partitioning, depend on their electronic and short-range local

Revealing the extent of disorder in amorphous oxides is one of the remaining puzzles in physical chemistry, glass sciences, and geochemistry. Here, we report the 27Al NMR results for amorphous Al2O3 thin films obtained from two different deposition methods (i.e., physical vapor-deposition and atomic layer-deposition), revealing two distinct amorphous states defined by a fraction of five-coordinated Al ([5]Al). The fractions of [4]Al and [5]Al are dominant (∼92−95%) in both films. While the overa

Despite their strong implications for magmatic processes in the earth's interior and pressure-induced structural changes in other amorphous, covalent oxide materials, little is known, beyond the coordination numbers of the framework cations, about the structures of silicate melts and glasses at high pressure. Here, we use multinuclear (27Al and 17O) solid-state NMR and quantum chemical calculations to study the structures of silicate glasses quenched from melts at pressures up to 10 GPa in a mul

We report spectroscopic evidence for the pressure-induced structural changes in B2O3 glass quenched from melts at pressures up to 6 GPa using solid-state NMR. While all borons are tri-coordinated at 1 atm, the fraction of tetra-coordinated boron increases with pressure, being about 5% and 27% in the B2O3 glass quenched from melts at 2 and 6 GPa, respectively. The fraction of boroxol ring species increases with pressure up to 2 GPa and apparently decreases with further compression up to 6 GPa. Tw