Formation of Ba2TiGe2O8 phase in BaO–TiO2–GeO2 glasses and their optical non-linearities

Abstract Second-order optical non-linearities for the transparent Ba 2 TiGe 2 O 8 (BTG) crystallized glasses with the composition of 40BaO · 20TiO 2 · 40GeO 2 (BTG40), 33.3BaO · 16.7TiO 2 · 50GeO 2 (BTG50) and 30BaO · 15TiO 2 · 55GeO 2 (BTG55) have been examined. A very large d 33 value for a transparent BTG crystallized glass in BTG55 was achieved, i.e., d 33 = 22 ± 3 pm/V, being comparable to that of LiNbO 3 single crystal. The d 33 for BTG50 and BTG40 were measured to be 12 ± 3 pm/V and 7 ± 2 pm/V, respectively. This result indicates that d 33 decreases with GeO 2 concentration, when approaching the glass composition of the stoichiometric BTG crystal. For a larger d 33 value in BTG crystallized glasses, it is considered that the high homogeneity of the oriented surface Ba 2 TiGe 2 O 8 crystalline layer on the crystallized BTG55 glass is accomplished by a suitable amount of benitoite phase of BaTiGe 3 O 9 , which acts a nucleation site for the BTG crystal.