  The phase diagram of the lithium niobate and lithium tantalate solid
solutions was investigated using experimental data from differential thermal
analysis (DTA) and crystal growth. We used XRF analysis to determine the
elemental composition of crystals. Based on the Neumann-Kopp rule, essential
data of end members lithium niobate (LN) and lithium tantalate (LT) was
created. The heats of fusion of end members given by DTA measurements of LN
(103 kJ/mol at 1531 K) and LT (289 kJ/mol at 1913 K) were given as input
parameters to generate the data. This data served as the basis for calculating
a phase diagram for LN and LT solid solutions. Finally, based on the
experimental data and thermodynamic solution model, the phase diagram was
optimized in the Calphad Factsage module. We also generated thermodynamic
parameters for Gibb's excess energy of the solid solution. A plot of
segregation coefficient as a function of Ta concentration was derived from the
phase diagram.
