Crystallization and physical properties of alkali phosphomolybdate glasses containing niobium oxide

Glasses with transition metal ions have interest because of their potential use in electrochemical, electronic and electro-optical devices. Molybdenum oxide is not a glass-forming, but it is able to enter the glass structure in the form of MoO4 tetrahedral or MoO6 octahedral with some glass-forming, like P2O5. The binary MoO3-P2O5 glasses were stable over a wide range of compositions. The ternary glass P2O5-MoO3-Li2O presents high potentiality as fast ion-conductors. Ferroelectric crystalline particles (LiNbO3) can be obtained by heat-treatments of the glass P2O5-Li2O-Nb2O5. The heat-treatment does not promote glass-ceramics with a single crystalline phase. The quaternary system P2O5-MoO3-Nb2O5-X2O, (X=Li, Na), prepared by melt quenching, allowed the control of the crystalline phases obtained by heat-treatments. In this work, the transparent as-prepared glasses were heat-treated at 550 C and 650 C for 4 hours. The structure of the samples was analyzed by differential thermal analyses (DTA), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. The change of the MoO3/P2O5 ratio is the main chemical parameter that governs the nucleation and growth of different crystallites. The decrease of this ratio induces the formation of non-linear optical NbOPO4 crystallites in the glass. The increase of the ratio leads to the formation of other phases, such as LiPO3 (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)