Crystallization behavior and microstructure investigations on LaF3 containing oxyfluoride glass ceramics

Er3+-doped transparent oxyfluoride glass ceramics containing LaF3 nanocrystals were prepared by melt quenching method. On the basis of DSC curves, it was observed that the addition of ErF3 decreases the LaF3 crystallization temperature. The crystallization kinetics studies for 4% ErF3 doped glass showed the average activation energy Ea to be 286 kJ/mol and the mean Avrami exponent n lies in the range of 1.0-1.5, indicating a diffusion-controlled growth process of particles of some initial volume in the glass system. EDS measurements suggested the incorporation of Er3+ into LaF3 crystalline phase, and a reduction of the lattice parameters of hexagonal LaF3 (P3¯c1) with increasing substitution of Er3+ for La3+ ions was identified by XRD. The modification of crystallites size with the addition of ErF3 indicated that trace additives suppress crystal growth by increasing nucleus quantity, while more additives produce larger crystallite size. After appropriate heat treatment, TEM evidenced the presence of nearly spherical LaF3 crystallites with 10-40 nm in size, which varies mainly with the content of ErF3. HRTEM images revealed that there are lots of lattice defects in LaF3 crystallites of the ErF3 doped sample, but a little in that of the ErF3 free sample after identical heat treatment.