Heat capacity of samarium titanates and phase equilibria of Sm2O3-TiO2 system

Highlights: • Heat capacities of Sm₂TiO₅ and Sm₂Ti₂O₇ are measured and the data are negative deviation from Neumann-Kopp rule calculation. • The existence of Sm₄Ti₃O₁₂ above 1942K and the translation of Sm₂TiO₅ between orthorhombic and hexagonal are detected. • Assessment on the Sm₂O₃-TiO₂ system is carried out and a set of self-consistent thermodynamic database is set up. • The irrationality of literature data is discussed and pointed out. • Based on enthalpies of formation, thermodynamics stability of RE₂TiO₅ and RE₂Ti₂O₇ is positive with the RE³⁺ ionic radius. -- Abstract: Sm₂TiO₅ and Sm₂Ti₂O₇ rare earth are synthesized by solid state reaction in air at temperature 1673 K using Sm₂O₃ and TiO₂ oxides as starting materials. Their high temperature heat capacities and phase transformation properties are determined by differential scanning calorimetry and ultra-high temperature differential thermal analysis, respectively. This work detects the structure transformation between orthorhombic and hexagonal Sm₂TiO₅ and confirms the existence of Sm₄Ti₃O₁₂ above 1945 K by quenching the laser melted samples. CALPHAD assessment of Sm₂O₃–TiO₂ system is performed based on new and published experimental data.