Phase transitions induced by solid solution in stuffed derivatives of quartz: A powder synchrotron XRD study of the LiAlSiO4-SiO2 join

The crystal structures of stuffed derivatives of quartz within the Li1-xAl1 -xSi1+xO4 system have been refined by Rietveld analysis of powder synchrotr on X-ray diffraction (XRD) data. Our results reveal an Al-Si order-disorder transition at x = similar to 0.3 and a beta-alpha displacive transformatio n at x = similar to 0.65. Structural variations across the series result fr om an interplay of three mechanisms: tetrahedral tilting associated with Al -Si order-disorder; Li positional disorder along structural channels parall el to c; and tetrahedral rotation related to the beta-alpha transition. At both microscopic (local bonding) and macroscopic (spontaneous strain) scale s, the substitution of Li+ and Al3+ for Si4+ closely mimics temperature in its effect on the quartz framework.