Experimental and theoretical study on elastic properties of crystalline alkali silicate hydrate

Abstract

Mechanical properties of synthesized sodium silicate mineral, Na-kanemite, was investigated by synchrotron-based high-pressure x-ray diffraction experiment and first-principles calculations. Under hydrostatic pressure, the 020 interlayer peak was substantially diffused while a new 011 peak formed at 0.4 GPa due to the reduction of Pbcn symmetry. Upon unloading, the diffused interlayer peak reappeared to its original position with a less peak intensity and the newly formed peak disappeared. This temporal but reversible phase instability related to the symmetry reduction, can be induced from the vibration effect of water molecules contained in interlayer region that can more significantly affect the structural response of crystals with poor crystallinity and stacking disorder. There is a good agreement of pressure response between experimental data and calculations using GGA functional. In addition, conducted analysis on bond variation revealed that contraction of thickness and distortion of Na layer under pressure which caused partial charge redistribution. Suggested elastic properties and charge data will be used to develop reliable force-field database for further molecular dynamics simulation and diagnose macroscopic impact from alkali-silicate reaction damaged structure. Keywords: Na-kanemite, High pressure x-ray diffraction, Density functional theory, First-principles calculation, Mechanical properties, Elastic coefficients