Effects of high pressure on stability of the nanocrystalline LiAlSi ₂O₆ phase of a glass-ceramic composite: A synchrotron X-ray diffraction study

Synchrotron X-ray diffraction studies, under pressures up to 50 GPa, have been performed on a 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 a diamond anvil cell on compression and decompression cycles with the aim of probing the effect of high-pressure compression on the nanocomposite structure. On the compression cycle from ambient pressure up to 20 GPa the unit cell volume of the LiAlSi₂O₆ phase decreased by about 22%. The diffraction patterns also revealed the presence, at high pressures, of the ZrTiO₄ phase that was nucleated in the matrix prior to the crystallization of the main LiAlSi₂O₆ phase. After quenching from 50 GPa to close to ambient conditions the diffraction pattern indicated that the high-pressure phase was retained to some extent although the decompressed structure still carried the signature of the initial ambient LiAlSi₂O₆ phase. A Birch-Murnaghan fit of the unit cell volume as a function of pressure yielded a zero pressure bulk modulus K0=71±2GPa and its pressure derivative K0′=4.4±0.6GPa for the nanocrystalline phase.