Colmenero Francisco, Plášil Jakub, Cobos Joaquín, Sejkora Jiří, Timón Vicente, Čejka Jiří, Fernández Ana María, Petříček Václav
Instituto de Estructura de la Materia (IEM-CSIC) C/Serrano, 113 28006 Madrid Spain
Institute of Physics ASCR, v.v.i. Na Slovance 2 182 21 Praha 8 Czech Republic.
RSC Adv. 2019 Dec 9;9(69):40708-40726. doi: 10.1039/c9ra09047a. eCollection 2019 Dec 3.
The full crystal structure of the copper-uranyl tetrahydroxide mineral (vandenbrandeite), including the positions of the hydrogen atoms, is established by the first time from X-ray diffraction data taken from a natural crystal sample from the Musonoi Mine, Katanga Province, Democratic Republic of Congo. The structure is verified using first-principles solid-state methods. From the optimized structure, the mechanical and dynamical stability of vandenbrandeite is studied and a rich set of mechanical properties are determined. The Raman spectrum is recorded from the natural sample and determined theoretically. Since both spectra have a high-degree of consistence, all spectral bands are rigorously assigned using a theoretical normal-coordinate analysis. Two bands in the Raman spectra, located at 2327 and 1604 cm, are recognized as overtones and a band at 1554 cm is identified as a combination band. The fundamental thermodynamic functions of vandenbrandeite are computed as a function of temperature using phonon calculations. These properties, unknown so far, are key-parameters for the performance-assessment of geological repositories for storage of radioactive nuclear waste and for understanding the paragenetic sequence of minerals arising from the corrosion of uranium deposits. The thermodynamic functions are used here to determine the thermodynamic properties of formation of vandenbrandeite in terms of the elements and the Gibbs free-energies and reaction constants for a series of reactions involving vandenbrandeite and a representative subset of the most important secondary phases of spent nuclear fuel. Finally, from the thermodynamic data of these reactions, the relative stability of vandenbrandeite with respect to these phases as a function of temperature and in the presence of hydrogen peroxide is evaluated. Vandenbrandeite is shown to be highly stable under the simultaneous presence of water and hydrogen peroxide.
首次从刚果民主共和国加丹加省穆索尼伊矿采集的天然晶体样本的X射线衍射数据中确定了铜铀酰四氢氧化物矿物（钒铜铀矿）的完整晶体结构，包括氢原子的位置。使用第一性原理固态方法对该结构进行了验证。根据优化后的结构，研究了钒铜铀矿的力学和动力学稳定性，并确定了一系列丰富的力学性能。从天然样本中记录了拉曼光谱并进行了理论计算。由于这两种光谱具有高度一致性，因此使用理论正则坐标分析对所有光谱带进行了严格归属。拉曼光谱中位于2327和1604 cm处的两个谱带被识别为泛音，1554 cm处的谱带被确定为组合带。使用声子计算计算了钒铜铀矿的基本热力学函数随温度的变化。这些迄今为止未知的性质是评估放射性核废料地质储存库性能以及理解铀矿床腐蚀产生的矿物共生序列的关键参数。这里使用热力学函数根据元素以及一系列涉及钒铜铀矿和乏核燃料最重要次生相的代表性子集的反应的吉布斯自由能和反应常数来确定钒铜铀矿形成的热力学性质。最后，根据这些反应的热力学数据，评估了钒铜铀矿相对于这些相在温度和过氧化氢存在下的相对稳定性。结果表明，在水和过氧化氢同时存在的情况下，钒铜铀矿具有高度稳定性。
