Insitu Study Of The Crustallization Mechanism In Linbo3-Sio2 Glasses

A crystallisation study of lithium niobium silicate glass with the molar composition 35Li2O.25Nb205.4OSiO2 is reported using in situ techniques at high temperatures. Those techniques reveal that the surface crystallisation begins at Tg with c-axis crystallites oriented perpendicular to the surface. Precipitation of nuclei, followed by growth and coalescence processes, induce the formation of particles and spherulites 0.5-4um diameter in size. A strong difference between surface and bulk crystallisation has been observed with bulk crystallisation yielding to 30 um diameter size spherulites. Those original spherulite shapes could be the origin of the macroscopic bulk second harmonic generation (SHG) signal.