Core/Shell Nanocrystalline Clusters in a Glass Matrix: A High Pressure Synchrotron X-Ray Diffraction Study*

Synchrotron x-ray diffraction studies up to 50 GPa were performed on an optically transparent composite with nanometer-sized ZrTiO$_{4}$/LiAlSi$_{2}$O$_{6}$ core/shell clusters embedded in a host glass. In the low-pressure range the shift and broadening of the x-ray diffraction lines was consistent with the densification of the LiAlSi$_{2}$O$_{6}$ shell phase. At higher pressures, the considerable diffraction line broadening pointed to a partial amorphization of the nanocrystalline phase. With pressure increase the x-ray patterns progressively revealed the presence of the ZrTiO$_{4}$ core phase. Upon decompression from 50 GPa to ambient conditions the pressure-induced changes were not fully reversible, however the diffraction pattern of the pressure-quenched material suggested that the decompressed structure carries the signature of the initial ambient LiAlSi$_{2}$O$_{6}$ phase.