KLaF4 nanocrystallisation in oxyfluoride glass-ceramics

Nanocrystallisation of the cubic and hexagonal polymorphs of KLaF4 in a 70SiO(2)-7Al(2)O(3)-16K(2)O-7LaF(3) (mol%) glass has been achieved by heat treatment above the glass transition temperature. For treatment at 580 degrees C, only the cubic structure crystallises, with a maximum crystallite size of similar to 9 nm. At higher temperatures, crystallisation of the hexagonal structure also takes place. The crystallisation process has been analysed using several thermal and structural techniques and is revealed to occur from a constant number of nuclei. The formation of a viscous barrier which inhibits further crystal growth and limits the crystal size to the nanometric range is observed. The title materials doped with lanthanide ions may be good candidates for optical applications