Kauric Guilhem, Epifano Enrica, Martin Philippe M, van Eijck Lambert, Bouëxière Daniel, Clavier Nicolas, Guéneau Christine, Smith Anna L
DEN-Service de la Corrosion et du Comportement des Matériaux dans leur Environnement (SCCME), CEA, Université Paris-Saclay, F-91191, Gif-sur Yvette, France.
Faculty of Applied Sciences, Radiation Science & Technology Department, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands.
Inorg Chem. 2020 May 4;59(9):6120-6130. doi: 10.1021/acs.inorgchem.0c00210. Epub 2020 Apr 20.
Neutron diffraction, X-ray absorption spectroscopy (XAS), and Raman spectroscopy measurements of the quaternary perovskite phase BaNaMoO have been performed in this work. The cubic crystal structure in space group 3̅ 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) (α = 55.8 × 10 K), has been determined to be ∼2 times higher than that of the barium molybdates BaMoO and BaMoO. 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 (Δ°) for BaNaMoO(cr) has been determined to be -(2524.75 ± 4.15) kJ mol 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)O fuel and sodium coolant.
在本工作中，对四方钙钛矿相BaNaMoO进行了中子衍射、X射线吸收光谱（XAS）和拉曼光谱测量。使用Rietveld方法对空间群为3̅的立方晶体结构进行了精修。在Mo K边进行的X射线吸收近边结构光谱（XANES）测量证实了钼的六价态。利用扩展X射线吸收精细结构（EXAFS）光谱对钼八面体的局部结构进行了详细研究。将Mo - O和Mo - Ba距离与中子衍射数据进行了比较，结果吻合良好。使用高温X射线衍射（HT - XRD）在303 - 923 K温度范围内测量的热膨胀系数（α = 55.8 × 10⁻⁶ K⁻¹），确定比钼酸钡BaMoO₄和BaMoO₃的热膨胀系数高约2倍。此外，通过HT - XRD、拉曼光谱和差示扫描量热法，在高达1473 K的温度下均未观察到相变或熔化现象。此外，使用溶液量热法在298.15 K下确定了BaNaMoO(cr)的标准生成焓（ΔfH°）为 - (2524.75 ± 4.15) kJ mol⁻¹。最后，通过计算在液态钠中形成四元化合物所需的阈值氧势，评估了钠冷快堆（SFR）的安全运行裕度，该阈值氧势是在辐照混合氧化物（U,Pu）O₂燃料与钠冷却剂相互作用后得出的。
