Phase Equilibrium Investigations and Thermodynamic Study of the Y2O3-Ta2O5 System

Two methods were used to investigate the Y2O3-Ta2O5 system: the equilibration method, which covered temperatures from 1573 to 1973 K, and the DTA method, which reached up to 2473 K. Phase identification was carried out using x-ray diffraction and scanning electron microscopy with energy-dispersive x-ray spectroscopy (SEM/EDX). The temperature of the eutectic reaction, L -> YTa3O9 (P) + Ta2O5, was determined to be 2019 K, with the corresponding eutectic composition being 78 mol.% Ta2O5. The study presents evidence that contradicts the existence of the eutectic reaction L -> YTaO4 (T) + YTa3O9 (P). Instead, it identifies a peritectic reaction L + YTaO4 (T) -> YTa3O9 (P), which was observed at a temperature of around 2075 K. Additionally, the heat capacity of the YTa3O9 (P) phase was measured using differential scanning calorimetry (DSC) over the temperature range from 240 to 1300 K. The results of this experimental investigation will lead to the development of a thermodynamic database for the Y2O3-Ta2O5 system.