The dissociation and ionization of LiNbO₃ melts

The thermodynamic and kinetic behavior of LiNbO₃ melts has been studied experimentally by differential thermal analysis (DTA). Theoretical modeling has been carried out for three cases and the predicted results matched to the experimental data: (1) the melt contains only one species and no chemical reactions are present during heating and cooling, (2) the melt contains three species and a dissociation/recombination reaction occurs between LiNbO₃ and Li₂O+Nb₂O₅ and (3) the melt contains seven species with both dissociation and ionization reactions occuring to form the additional species Li⁺, LiO^-, Nb₂O₄V²⁺_O, and O^2-. The best fit, using the linear programming technique LINDO, was for case 3 with seven active species in the melt. ΔG - values, ΔH - values and reaction rate constants (β - values) were found for the dissociation/recombination reaction as well as for the two ionization reactions. These values allowed the species populations to be calculated for both the congruent liquid (mole ratio of Li₂O to Nb₂O₅ = k = 0.942) and the Nb - rich (k = 0.724) and Li - rich (k = 1.222) liquid cases studied experimentally by DTA at 1275°C.