Structural and thermodynamic study of dicesium molybdate Cs2Mo2O7: Implications for fast neutron reactors

A. L. Smith, G. Kauric, L. van Eijck, K. Goubitz, Gilles Wallez, Jean Christophe Griveau, E Colineau, N. Clavier, R. J.M. Konings

Research output: Contribution to journalArticleScientificpeer-review

9 Citations (Scopus)

Abstract

The structure of α-Cs2Mo2O7 (monoclinic in space group P21/c), which can form during irradiation in fast breeder reactors in the space between nuclear fuel and cladding, has been refined in this work at room temperature from neutron diffraction data. Furthermore, the compounds' thermal expansion and polymorphism have been investigated using high temperature X-ray diffraction combined with high temperature Raman spectroscopy. A phase transition has been observed at Ttr(α→β)=(621.9±0.8) K using Differential Scanning Calorimetry, and the structure of the β-Cs2Mo2O7 phase, orthorhombic in space group Pbcm, has been solved ab initio from the high temperature X-ray diffraction data. Furthermore, the low temperature heat capacity of α-Cs2Mo2O7 has been measured in the temperature range T=(1.9–313.2) K using a Quantum Design PPMS (Physical Property Measurement System) calorimeter. The heat capacity and entropy values at T=298.15 K have been derived as Cp,m o(Cs2Mo2O7,cr,298.15K)=(211.9±2.1)JK−1mol−1 and Sm o(Cs2Mo2O7,cr,298.15K)=(317.4±4.3)JK−1mol−1. When combined with the enthalpy of formation reported in the literature, these data yield standard entropy and Gibbs energy of formation as ΔfSm o(Cs2Mo2O7,cr,298.15K)=−(628.2±4.4)JK−1mol−1 and ΔfGm o(Cs2Mo2O7,cr,298.15K)=−(2115.1±2.5)kJmol−1. Finally, the cesium partial pressure expected in the gap between fuel and cladding following the disproportionation reaction 2Cs2MoO4=Cs2Mo2O7+2Cs(g)+ 1/2 O2(g) has been calculated from the newly determined thermodynamic functions.

Original languageEnglish
Pages (from-to)89-102
Number of pages14
JournalJournal of Solid State Chemistry
Volume253
DOIs
Publication statusPublished - 1 Sep 2017

Keywords

  • Cesium dimolybdate
  • Neutron diffraction
  • Phase transitions
  • Raman spectroscopy
  • Thermal expansion

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