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 Li(1-x)Al(1-x)Si(1+x)O₄ system have been refined by Rietveld analysis of powder synchrotron X-ray diffraction (XRD) data. Our results reveal an Al-Si order-disorder transition at x = ~0.3 and a β-α displacive transformation at x = ~0.65. Structural variations across the series result from an interplay of three mechanisms: tetrahedral tilting associated with Al-Si order-disorder; Li positional disorder along structural channels parallel to c; and tetrahedral rotation related to the β-α transition. At both microscopic (local bonding) and macroscopic (spontaneous strain) scales, the substitution of Li⁺ and Al³⁺ for Si⁴⁺ closely mimics temperature in its effect on the quartz framework.