ZrTiO(4) crystallisation in nanosized liquid-liquid phase-separation droplets in glass - a quantitative XANES study

The crystallisation of the nucleation agent ZrTiO(4) in a low thermal-expansion lithium aluminosilicate glass-ceramics is monitored as a function of time by combining transmission electron microscopy with Ti-L(2,3) X-ray absorption near-edge structure spectroscopy. The formation of liquid-liquid phase-separation droplets is shown to precede ZrTiO(4) crystallisation within the latter nanosized droplets. Quantitative data on crystalline fractions enable conclusions on the self-limited growth of ZrTiO(4) 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 ZrTiO(4) 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.