Atomic force microscopy of early crystallisation stages Li2O.2SiO(2) glasses

Nucleation and crystallisation processes in glasses of Li2O . 2SiO(2) composition have been investigated both by scanning electron (SEM) and atomic force microscopies (AFM). Both single and double stage heat treatments were performed. Whereas the SEM results on glass fracture surfaces displayed reasonable coincidence with most of the numerous earlier investigations on that system, the AFM results revealed a totally new insight into these processes. Although the glasses heated to the maximum nucleation temperature were fully transparent, totally x-ray amorphous and did also not show any crystalline inclusions by SEM, the high resolution AFM gave evidence of nanostructural features with a width of 10-20 nm and a length of about 30 nm. They grew with a root 3t dependence to a width of about 50 nm and a length of about 80 nm for times up to I h, finally showing a nearly hexagonal habit. When these nucleated Li2O . 2SiO(2) glass samples were heated to the maximum crystal growth temperature some fully developed hexagonal crystals, 90-100 nm wide and 170-180 nm long, could be found. These early crystallisation stages demonstrate that the usually assumed independence of nucleation and crystallisation processes are not fulfilled for Li2O . 2SiO(2).