Core/shell ZrTiO₄/LiAlSi₂O₆ nanocrystals: A synchrotron X-ray diffraction study of high-pressure compression

In situ synchrotron X-ray diffraction studies have been performed on an optically transparent lithium-aluminosilicate glass-ceramic composite with nanometer-sized LiAlSi₂O₆ crystals embedded in a host matrix. The pressure-induced evolution of X-ray diffraction patterns was followed in compression up to 50 GPa and in subsequent decompression to ambient conditions. In the low-pressure range, the diffraction patterns illustrated a progressive shift and broadening of the diffraction lines consistent with a gradual densification of the LiAlSi₂O₆ phase. The unit cell volume of the LiAlSi₂O₆ nanocrystalline phase calculated for the compression sequence between ambient pressure and 12.5 GPa decreased by about 13.5%. At higher pressures, the diffraction patterns displayed considerable line broadenings indicating a partial amorphization of the nanocrystalline phase. Additionally, the patterns revealed the increasing presence of the ZrTiO₄ phase which was nucleated in the host matrix prior to the crystallization of the LiAlSi₂O₆ main nanocrystalline phase. The diffraction pattern of the composite quenched from 50 GPa to ambient pressure conditions did not show full reversibility of pressure-induced changes. Despite the dominating presence of the broad diffraction bands, the diffraction pattern of the pressure-quenched material suggested that the decompressed structure carries at least a partial signature of the initial ambient LiAlSi₂O₆ phase.