New transparent crystallized glasses with optical nonlinear LiBGeO4 crystals

Crystallization behaviors of the glass with a composition of 25Li(2)O.25B(2)O(3).50GeO(2) corresponding to lithium borogermanate LiBGeO4 have been examined. It has been confirmed that the LiBGeO4 crystalline phase is formed at the surface of heat-treated glasses. The second harmonic (SH) generation is found from transparent surface crystallized glasses, demonstrating for the first time that the LiBGeO4 phase shows optical nonlinearity. The SH intensity of LiBGeO4 crystallites (powdered state) prepared through crystallization is about ten times as large as that of pulverized alpha-quartz. The SH intensity of transparent crystallized glasses (bulk state) with crystalline layers of 3-4.5 mum thickness increases with increasing heat treatment temperature (540-560degreesC) and time (1-6 h), and the maximum SH intensity among the samples studied is in the order of 1/10 in comparison with that of alpha-quartz single crystal. The transparent crystallized glass obtained by heat treatment at 550alphaC for 3 h exhibits a clear and fine Maker fringe pattern, indicating a highly orientation of LiBGeO4 crystals at the surface

Evolution and characterization of fluorite-like nano-SrBi2Nb2O9SrBi_2Nb_2O_9 phase in the SrO−Bi2O3−Nb2O5−Li2B4O7SrO-Bi_2O_3-Nb_2O_5-Li_2B_4O_7 glass system

Transparent glasses of various compositions in the system $(100−x)Li_2B_4O_7 - x(SrO-Bi_2O_3-Nb_2O_5)$ (where x=10, 20, 30, 40, 50 and 60, in molar ratio) were fabricated via splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses. X-ray powder diffraction (XRD) and transmission electron microscopic studies confirmed the amorphous nature of the as-quenched and crystallinity in the heat-treated samples. Fluorite phase formation prior to the perovskite $SrBi_2Nb_2O_9$ phase was analyzed by both the XRD and high-resolution transmission electron microscopy. Dielectric and the optical properties (transmission, optical band gap and Urbach energy) of these samples have been found to be compositional dependent. Refractive index was measured and compared with the values predicted by Wemple–Didomemenico and Gladstone–Dale relations. The glass nanocomposites comprising nanometer-sized crystallites of fluorite phase were found to be nonlinear optic active

Second-order optical non-linearity initiated in Li2O-Nb2O5-SiO2 and Li2O-ZnO-Nb2O5-SiO2 glasses by formation of polar and centrosymmetric nanostructures

Amorphous nanoheterogeneities of the size less than 100 .ANG. have been formed in glasses of the Li2O-Nb2O5-SiO2 (LNS) and Li2O-ZnO-Nb2O5-SiO2 (LZNS) systems at the initial stage of phase sepn. and examd. by transmission electron microscopy, small-angle X-ray and neutron scattering. Both LNS and LZNS nanoheterogeneous glasses exhibit second harmonic generation (SHG) even when they are characterized by fully amorphous X-ray diffraction (XRD) patterns. Chem. differentiation and ordering of glass structure during heat treatments at appropriate temps. higher Tg lead to drastic increase of SHG efficiency of LNS glasses contrary to LZNS ones in the frame of amorphous state of samples. Following heat treatments of nanostructured glasses result in crystn. of ferroelec. LiNbO3 and non-polar LiZnNbO4 in the LNS and LZNS glasses, resp. Taking into account similar polarizability of atoms in LNS and LZNS glasses, the origin of the principal difference in the second-order optical non-linearity of amorphous LNS and LZNS samples is proposed to connect predominantly with the internal structure of formed nanoheterogeneities and with their polarity. Most probably, amorphous nanoheterogeneities in glasses may be characterized with crystal-like structure of polar (LiNbO3) phase initiating remarkable SHG efficiency or non-polar (LiZnNbO4) phase, which do not initiate SHG activity. It gives an opportunity to vary SHG efficiency of glasses in a wide rage without remarkable change of their transparency by chem. differentiation process at the initial stage of phase sepn. when growth of nanoheterogeneities is 'frozen'. At higher temps., LiNbO3 crystals identified by XRD ppt. in LNS glasses initiating even more increase of SHG efficiency but visually observable transparency is impaired