ZrTiO4 crystallisation in nanosized liquid–liquid phase-separation droplets in glass—a quantitative XANES study

The crystallisation of the nucleation agent ZrTiO4 in a low thermal-expansion lithium aluminosilicate glass-ceramics is monitored as a function of time by combining transmission electron microscopy with Ti-L2,3 X-ray absorption near-edge structure spectroscopy. The formation of liquid–liquid phase-separation droplets is shown to precede ZrTiO4 crystallisation within the latter nanosized droplets. Quantitative data on crystalline fractions enable conclusions on the self-limited growth of ZrTiO4 nanocrystals in low thermal-expansion glass-ceramics and based on Avrami's equation, the growth is shown to be restricted by a barrier (the outer border of the phase-separation droplet). It is shown that liquid–liquid phase separation and crystallisation are temporally decoupled. The size of ZrTiO4 crystallites is determined by the restricted volume of the phase-separation droplets they crystallise in. The volume of the droplets in turn is restricted by the formation of a diffusion barrier in the surrounding residual glass.