Heat capacity and thermodynamic functions of rare earth Oxyfluorides, REOF

Abstract

This study investigates the heat capacity and thermodynamic properties of rare earth oxyfluorides (REOF), focusing on NdOF, YOF, and YbOF-monoclinic. To increase our understanding of their physical properties and stability, we measured the heat capacities of these REOF materials over a temperature range of 1.8 to 300 K. Our results reveal several Schottky anomalies at low temperatures due to interactions involving rare earth nuclei with nonzero magnetic moments and electronic contributions. We fitted the experimental data using theoretical models to derive standard entropy, enthalpy, and Gibbs energy. These values were combined with literature values to calculate Gibbs energies of formation from the elements and the fluorides and oxides at selected temperatures. At 298.15 K, the Gibbs energy of formation relative to oxides and fluorides was calculated to be −26.717 kJ·mol⁻¹, −12.394 kJ·mol⁻¹, and −11.011 kJ·mol⁻¹for NdOF, YOF, and YbOF-mon, respectively. The Gibbs energy of formation of REOF relative to the elements at 298.15 K was calculated to be −1143.889 kJ·mol⁻¹, −1191.304 kJ·mol⁻¹, and −1115.430 kJ·mol⁻¹ for NdOF, YOF, and YbOF-mon, respectively. The results confirm the stability of these three REOF compounds, underlining their potential for diverse technological applications.