Electronic polarizability and crystallization of K2O–TiO2–GeO2 glasses with high TiO2 contents

Some K2O–TiO2–GeO2 glasses with a large amount of TiO2 contents (15–25 mol%) such as 25K2O–25TiO2–50GeO2 have been prepared, and their electronic polarizability, Raman scattering spectra, and crystallization behavior are examined to clarify thermal properties and structure of the glasses and to develop new nonlinear optical crystallized glasses. It is proposed that the glasses consist of the network of TiO6 and GeO4 polyhedra. The glasses show large optical basicities of image, indicating the high polarizabity of TiOn (image) polyhedra in the glasses. K2TiGe3O9 crystals are formed through crystallization in all glasses prepared in the present study. In particular, 20K2O–20TiO2–60GeO2 glass shows bulk crystallization and 18K2O–18TiO2–64GeO2 glass exhibits surface crystallization giving the c-axis orientation. The crystallized glasses show second harmonic generations (SHGs), and it is suggested that the distortion of TiO6 octahedra in K2TiGe3O9 crystals induces SHGs.