Crystallization behavior and microstructure investigations on LaF 3 containing oxyfluoride glass ceramics

Abstract

Er 3+-doped transparent oxyfluoride glass ceramics containing LaF 3 nanocrystals were prepared by melt quenching method. On the basis of DSC curves, it was observed that the addition of ErF 3 decreases the LaF 3 crystallization temperature. The crystallization kinetics studies for 4% ErF 3 doped glass showed the average activation energy E a 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 Er 3+ into LaF 3 crystalline phase, and a reduction of the lattice parameters of hexagonal LaF 3 ( P 3 ¯ c 1 ) with increasing substitution of Er 3+ for La 3+ ions was identified by XRD. The modification of crystallites size with the addition of ErF 3 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 LaF 3 crystallites with 10–40 nm in size, which varies mainly with the content of ErF 3. HRTEM images revealed that there are lots of lattice defects in LaF 3 crystallites of the ErF 3 doped sample, but a little in that of the ErF 3 free sample after identical heat treatment.