Transport Characterization of Cerium Dioxide Pressed Powders at Low Temperatures
Loading...
Date
2021-08-26
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
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.
Description
Keywords
CeO2, Cerium Dioxide, Low Temperature, Heat Capacity, Thermal Conductivity