Thermodynamic properties of neodymium silicates at high temperature (298.15–1273K) and thermodynamic reassessment of the Nd2O3-SiO2 system

Solid oxide fuel cells (SOFCs) have garnered significant interest due to their potential as alternative electrical power generation systems that offer low pollutant emissions and high energy conversion efficiency. Neodymium silicates have emerged as promising electrolyte materials owing to their high ionic conductivity. To enhance our understanding of their performance in SOFC applications, it is essential to investigate the thermodynamic properties of neodymium silicates. In this study, we measured the heat capacities of the prepared samples over the temperature range of 673–1273 K using a multi-high temperature calorimeter (MHTC) 96 line. The temperature dependence of heat capacities for Nd₂SiO₅, Nd₁₄Si₉O₃₉, and Nd₂Si₂O₇ were modeled as functions: Cp_(Nd2SiO5) = 194.7 + 0.028 T–4,714,800 T⁻² – 239.75 T^−0.5 + 491568400 T⁻³ (J·mol⁻¹·K⁻¹) (298.15 - 1400K), Cp_(Nd14Si9O39) =1527.1 + 0.22 T − 40097000 T⁻² – 2150.3 T^−0.5 + 4424200000 T⁻³ (J·mol⁻¹·K⁻¹) (298.15 - 1400K), Cp_(Nd2Si2O7) =276 + 0.032 T − 8261400 T⁻² – 480 T^−0.5 + 983136800 T⁻³ (J mol⁻¹ K⁻¹) (298.15–1400K), and then used for computing changes in entropy and Gibbs free energy. The Nd₂O₃-SiO₂ system was reassessed based on the phase diagram experimental data and measured heat capacities in this work.