Crystallization and Nonlinear Optical Properties of Potassium Niobium Silicate Glasses

The crystallization of the xK^sub 2^O · xNb^sub 2^O^sub 5^· (1 - 2x)SiO^sub 2^(x= 0.167-0.250) glasses and glasses close in composition to K^sub 2^O · Nb^sub 2^O^sub 5^· 4SiO^sub 2^at the ratio K^sub 2^O : Nb^sub 2^O^sub 5^≠ 1 is investigated. In high-silica glasses, the metastable phase separation followed by the bulk multiphase crystallization are observed at temperatures close to the glass transition point T^sub g^. The nanostructured transparent glasses that exhibit the optical second harmonic generation (SHG) effect are formed at the early stages of phase separation. The surface crystallization of glasses with the precipitation of the KNbSi^sub 2^O^sub 7^noncentrosymmetric phase occurs at higher temperatures.[PUBLICATION ABSTRACT]