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Becquerelite mineral phase: crystal structure and thermodynamic and mechanical stability by using periodic DFT

机译：Bececrite矿物相：使用周期性DFT晶体结构和热力学和机械稳定性

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摘要

The structure, thermodynamic and mechanical properties of becquerelite mineral, Ca(UO2)(6)O-4(OH)(6)center dot 8H(2)O, were studied by means of theoretical solid-state calculations based on density functional theory using plane waves and pseudopotentials. The positions of the hydrogen atoms in the unit cell of becquerelite mineral were optimized theoretically since it was not possible to determine them from X-ray diffraction data by structure refinement. The structural results, including the lattice parameters, bond lengths and X-ray powder pattern, were found to be in excellent agreement with their experimental counterparts. The fundamental thermodynamic properties of becquerelite mineral, including specific heat, entropy, enthalpy and Gibbs free energy, were then computed by performing phonon calculations at the computed optimized structure. Since the experimental values of these properties are unknown, their values were predicted. The values obtained for the isobaric specific heat and entropy of becquerelite at the temperature of 298.15 K were 148.4 and 172.3 J K-1 mol(-1), respectively. The computed thermodynamic properties were combined with those of the corresponding elements in order to obtain the enthalpy and Gibbs free energy of formation as a function of temperature. The availability of these thermodynamic properties of formation allowed to determine the enthalpies and free energies and associated reaction constants of a series of reactions involving becquerelite and other uranyl containing materials. Futhermore, knowledge of these properties permitted the study of the thermodynamic stability of becquerelite with respect to a rich set of secondary phases of spent nuclear fuel, including dehydrated schoepite, schoepite, metaschoepite, studtite, metastudtite, rutherfordine and soddyite under different conditions of temperature. Becquerelite is shown to be highly stable in the presence of hydrogen peroxide. It is the second most stable phase under intermediate hydrogen peroxide concentrations (after schoepite), and the fourth most stable phase under high hydrogen peroxide concentrations (after studtite, schoepite and metaschoepite). Finally, the equation of state and elastic properties of this mineral, unknown to date, were determined. The crystal structure of becquerelite was found to be stable mechanically and dynamically. Becquerelite can be described as a brittle material exhibiting large anisotropy and large compressibility in the direction perpendicular to the sheets characterizing the structure of this layered uranyl containing material. The dependence of the elastic properties of becquerelite with respect to the strain orientation is shown to be analogous to that of schoepite mineral. The calculated bulk modulus is also very similar to that of schoepite, B similar to 31 GPa.
机译：通过基于密度功能理论的理论固态计算研究了BECREKETITE矿物质，CA（UO2）（6）O-4（OH）（6）中心点8H（2）O的结构，热力学和力学性能使用平面波和伪软件。理论上优化了BECORELITE矿物的单位细胞中氢原子的位置，因为不可能通过结构细化从X射线衍射数据中确定它们。发现包括晶格参数，粘合长度和X射线粉末图案的结构结果与实验同行非常好。然后通过在计算的优化结构上执行声子计算来计算BECERELITE矿物质的基本热力学性质，包括比热，熵，焓和吉布斯自由能。由于这些属性的实验值未知，因此预测其值。在298.15k的温度下，为Beckerelite的等异质热和熵的值分别为148.4和172.3JK-1mol（-1）。将计算的热力学性质与相应元件的那些合并，以获得作为温度的函数的形成焓和吉布斯自由能。这些热动力学性质的可用性允许确定涉及Beckerelite和其他含叔芳基材料的一系列反应的焓和自由能和相关的反应常数。更加知识，这些物业的知识允许研究贝克利特的热力学稳定性，相对于富含废核燃料的丰富的二次阶段，包括脱水丘脑，脱庚岩，甲状腺素，Studtite，Metastudite，Rutherfordine和SODDyite在不同的温度条件下。 BECOREKELITE在过氧化氢的存在下表现出高度稳定。在中间氢氧化物浓度（斯基硫酸盐之后）下是第二个最稳定的相，以及在高氧化氢浓度下的第四最稳定的相（Steartite，Schoepite和MetasChoetch）。最后，确定了这种矿物质的状态和弹性特性，迄今为止未知。发现BECORELELITE的晶体结构机械和动态稳定。 BECORELELITE可以描述为脆性材料，其在垂直于表征该层状甲铀材料的结构的薄片的方向上具有大的各向异性和大的压缩性。 BECORELELITE相对于应变取向的弹性性质的依赖性被认为是类似于山素矿物质的。计算出的体积模量也非常类似于类似于31 GPa的斯基泰耐岩。

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  • 来源
    《RSC Advances》 |2018年第43期|共18页
  • 作者

    Colmenero Francisco; Maria Fernandez Ana; Timon Vicente; Cobos Joaquin;

  • 作者单位

    CSIC IEM C Serrano 123 Madrid 28006 Spain;

    Ctr Invest Energet Medioambientales &

    Tecnol CIEM Avda Complutense 40 Madrid 28040 Spain;

    CSIC IEM C Serrano 123 Madrid 28006 Spain;

    Ctr Invest Energet Medioambientales &

    Tecnol CIEM Avda Complutense 40 Madrid 28040 Spain;

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  • 正文语种 eng
  • 中图分类 化学;
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