Structural and Thermodynamic Investigation of the Perovskite Ba2NaMoO5.5

Journal article (2020)

Authors

Guilhem Kauric Université Paris-Saclay, Paris
E. Epifano RST/Reactor Physics and Nuclear Materials - AS
P. M. Martin Universite Montpellier, Marcoule
L. van Eijck RST/Neutron and Positron Methods in Materials - AS
D. Bouëxière European Commission Joint Research Centre
N. Clavier Universite Montpellier, Marcoule
A.L. Smith RST/Reactor Physics and Nuclear Materials - AS
Research Group
RST/Neutron and Positron Methods in Materials (AS) (TU Delft)
Copyright: © 2020 Guilhem Kauric, E. Epifano, Philippe M. Martin, L. van Eijck, Daniel Bouëxière, Nicolas Clavier, Christine Guéneau, A.L. Smith
DOI: https://doi.org/10.1021/acs.inorgchem.0c00210
More Info
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Published Date

2020

Language

English

Faculty

Applied Sciences

Department

RST/Radiation, Science and Technology

Research Group

RST/Neutron and Positron Methods in Materials

Abstract

Neutron diffraction, X-ray absorption spectroscopy (XAS), and Raman spectroscopy measurements of the quaternary perovskite phase Ba2NaMoO5.5 have been performed in this work. The cubic crystal structure in space group Fm3¯ m has been refined using the Rietveld method. X-ray absorption near-edge structure spectroscopy (XANES) measurements at the Mo K-edge have confirmed the hexavalent state of molybdenum. The local structure of the molybdenum octahedra has been studied in detail using extended X-ray absorption fine structure (EXAFS) spectroscopy. The Mo-O and Mo-Ba distances have been compared to the neutron diffraction data with good agreement. The coefficient of thermal expansion measured in the temperature range of 303-923 K, using high temperature X-ray diffraction (HT-XRD) (αV = 55.8 × 10-6 K), has been determined to be ∼2 times higher than that of the barium molybdates BaMoO3 and BaMoO4. Moreover, no phase transition nor melting have been observed, neither by HT-XRD nor Raman spectroscopy nor differential scanning calorimetry, up to 1473 K. Furthermore, the standard enthalpy of formation (ΔfHm°) for Ba2NaMoO5.5(cr) has been determined to be -(2524.75 ± 4.15) kJ mol-1 at 298.15 K, using solution calorimetry. Finally, the margin for safe operation of sodium-cooled fast reactors (SFRs) has been assessed by calculating the threshold oxygen potential needed, in liquid sodium, to form the quaternary compound, following an interaction between irradiated mixed oxide (U,Pu)O2 fuel and sodium coolant.