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

“…These crystal-like domains do not form else Bragg peaks on XRD patterns but they are already able to produce or not produce remarkable SHG activity depending on polarity of their atomic structure. The presence of polar fragments in glass structure was established earlier from dielectric spectroscopy data for the glass of the composition corresponding to ferroelectric Pb 5 Ge 3 O 11 [25]. It is probably, the contribution made to the polarizability of the LNS glasses by nanoheterogeneities with a medium-range order structure that resembles the structural motif of the LiNbO 3 ferroelectric is much larger than the corresponding contribution of nanoheterogeneities with a non-polar structure in the LNZS system.…”