| dc.description.abstract | Reported is an experimental and computational investigation of the low temperature heat capacity, thermodynamic functions, and thermal conductivity of stoichiometric, polycrystalline CeO₂. The experimentally measured heat capacity at T<15K provides an important correction to the historically accepted experimental values, and the low temperature thermal conductivity serves as the most comprehensive data set at T<400K available. Below 10 K, the heat capacity is observed to obey the Debye T³ law, with a Debye temperature of ΘD = 455 K. The entropy, enthalpy, and Gibbs free energy functions are obtained from the experimental heat capacity and compared with predictions from Hubbard-corrected density functional perturbation theory calculations done by colleagues. The thermal conductivity for stoichiometric CeO² is determined using the Maldanado continuous measurement technique, along with Laser Flash Analysis, and analyzed according to the Klemens-Callaway model. Further heat capacity measurements were done on nonstoichiometric CeO₂₋δ samples in order to investigate signs of an anomalous heat capacity contribution in historical experimental values. The low temperature heat capacity data for nonstoichiometric samples showed a Schottky anomaly characteristic of Zeeman splitting in a paramagnetic salt. This Schottky contribution shows a magnetic dependence typical of Zeeman splitting of ground state energy levels. The nonstoichiometric heat capacity measurements were fitted with a multi-level Schottky function, and then the entropy was calculated. This entropy scales with the number of oxygen vacancies in the lattice. These measurements show signs of a more complex magnetic structure that has so far been unreported in the literature for this material. | |
