Evaluation and Thermodynamic Optimization of Phase Diagram of Lithium Niobate Tantalate Solid Solutions

The phase diagram of the lithium niobate and lithium tantalate solidsolutions was investigated using experimental data from differential thermalanalysis (DTA) and crystal growth. We used XRF analysis to determine theelemental composition of crystals. Based on the Neumann-Kopp rule, essentialdata of end members lithium niobate (LN) and lithium tantalate (LT) wascreated. 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 inputparameters to generate the data. This data served as the basis for calculatinga phase diagram for LN and LT solid solutions. Finally, based on theexperimental data and thermodynamic solution model, the phase diagram wasoptimized in the Calphad Factsage module. We also generated thermodynamicparameters for Gibb's excess energy of the solid solution. A plot ofsegregation coefficient as a function of Ta concentration was derived from thephase diagram.