Temperature dependence of viscosity of molten lithium niobate

The viscosity is measured in different lithium niobate melts with congruent and stoichiometrical composition in the temperature range of 1500-1620 K. A larger Li2O content reduces the viscosity of the LiNbO3 melt. The viscosity of the stoichiometrical melt depends linearly on the temperature, but the viscosity of the congruent melt departs from a linear relationship. In the range of measured temperatures there is one activation process for the stoichiometrical melt, the activation energy of the viscous flow being E-b = 52.56 kJ/mol. For the congruent melt, there are two activation energies of viscous flow, the higher-temperature zone is E-b = 43.03 kJ/mol and the lower temperature zone 20K above the melting point E-b = 72.6 kJ/mol. The abrupt increase of the activation energy of the viscous flow may stem from the change of the structure of the congruent composition melt close to the melting point. (C) 2000 Published by Elsevier Science B.V. All rights reserved.