Transparent Ferroelectric Glass-Ceramics

In recent years, there has been a resurgence of interest in transparent ferroelectric glass-ceramics (TFGCs), which are a special class of glass-ceramic composites that combine the low cost of fabrication and forming of transparent glass with the superior nonlinear optical and electro-optical properties of ferroelectric crystals. In this paper, we present a review of the current status, focusing on the challenges of fabrication and opportunities for selectively creating nonlinear optical structures, which will be useful in realizing integrated optical devices. A successful fabrication of TFGC requires the nucleation and growth of crystallites that are too small to scatter light, yet large enough to have ferroelectric response. Early experiments on silica based glasses containing common ferroelectric oxides indicated that although the preparation of TFGC is feasible, such a balance of crystallite size is difficult to achieve. However, later studies have demonstrated successful fabrication of TFGCs with compositions based on high refractive index glass matrix (e.g. tellurites containing ferroelectric LiNbO3), or the ferroelectric oxides that form glass easily and then crystallize congruently (e.g. LaBGeO5). Surface crystallization dominates the devitrification of these compositions. Strong second harmonic generation of light has been observed in a number of glass-ceramic systems, which makes them attractive for applications but so far the ferroelectric behavior has been demonstrated for very few systems.