Heat capacities of lanthanide and actinide monazite-type ceramics

• Published in: Journal of nuclear materials Vol. 464; pp. 147 - 154
• Main Authors: Kowalski, Piotr M., Beridze, George, Vinograd, Victor L., Bosbach, Dirk
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-09-2015
• Subjects: Ceramics; Computation; Entropy; Heat capacity; Lanthanides; Monazite; Specific heat
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2015.04.032

•We computed the heat capacities of monazite-type ceramics.•For lanthanide monazites the ab initio calculations well reproduce the measurements.•The available experimental results on plutonium monazite require revision.
(Ln,An)xPO4 monazite-type ceramics are considered as potential matrices for the disposal of nuclear waste. In this study we computed the heat capacities and the standard entropies of these compounds using density functional perturbation theory. The calculations of lanthanide monazites agree well with the existing experimental data and provide information on the variation of the standard heat capacities and entropies along the lanthanide series. The results for AnPO4 monazites are similar to those obtained for the isoelectronic lanthanide compounds. This suggests that the missing thermodynamic data on actinide monazites could be similarly computed or assessed based on the properties of their lanthanide analogs. However, the computed heat capacity of PuPO4 appear to be significantly lower than the measured data. We argue that this discrepancy might indicate potential problems with the existing experimental data or with their interpretation. This shows a need for further experimental studies of the heat capacities of actinide-bearing, monazite-type ceramics.