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.