Crystallization and quartz inversion temperature of sol-gel derived LAS solid solutions

Crystallization and inversion temperature of sol-gel derived high-quartz solid solutions (HQss) of composition LixAlxSi1−xO2 (with 0 ≤ x ≤ 0.2) in the pseudo-binary system SiO2-LiAlO2 (LAS) are studied. Lithium, aluminum and silicon containing precursors are used to prepare a sol to coat seeded silicon wafers with a thin amorphous LAS film. Using lithium disilicate as a seed material, HQss is formed readily at temperatures >700 °C between the nominal compositions 83.3-100 mol% SiO2, whereas using zirconium titanate as seed, HQss crystallization is observed at higher temperatures (>950 °C) and only at the LiAl-rich side of the compositional join. HQss transforms to keatite solid solution and to high-cristobalite when heated above 1000-1100 °C, respectively. The chemical substitution of Si4+ by Al3+ + Li+ lead to an increase in the a0 unit cell parameter. In films of x < 0.193 a reversible transformation of high-to-low quartz solid solution is evident. The quartz inversion temperature Tc decreased linearly with increasing x. The dependence is best described by the equation Tc (°C) = (569 ± 3) − (2.82 ± 0.06)·103x.