Sandia National Laboratories, Albuquerque, NM 87185, USA.
Phys Chem Chem Phys. 2019 Nov 27;21(46):25569-25576. doi: 10.1039/c9cp04117f.
The relationship between the structure and thermodynamic properties of schoepite, an important uranyl phase with formula [(UO2)8O2(OH)12]·12H2O formed upon corrosion of UO2, has been investigated within the framework of density functional perturbation theory (DFPT). Experimental crystallographic lattice parameters are well reproduced in this study using standard DFT. Phonon calculations within the quasi-harmonic approximation predict standard molar entropy and isobaric heat capacity of S0 = 179.60 J mol-1 K-1 and C0P = 157.4 J mol-1 K-1 at 298.15 K, i.e., ∼6% and ∼4% larger than existing DFPT-D2 calculations. The computed variation of the standard molar isobaric heat capacity with water content from schoepite (UO3·xH2O, x = 2.25) to dehydrated schoepite (x = 1) is predicted to be essentially linear along isotherms ranging from 100 to 500 K. These findings have important implications for the dehydration of layered uranyl corrosion phases and hygroscopic materials.
在密度泛函微扰理论（DFPT）的框架内研究了作为 UO2 腐蚀产物的重要铀酰相——schoepite[(UO2)8O2(OH)12]·12H2O 的结构与热力学性质之间的关系。本研究使用标准 DFT 很好地再现了实验晶体学晶格参数。准谐近似下的声子计算预测 298.15 K 时标准摩尔熵和等压热容分别为 S0 = 179.60 J mol-1 K-1 和 C0P = 157.4 J mol-1 K-1，即比现有 DFPT-D2 计算结果大约 6%和 4%。预测从 schoepite（UO3·xH2O，x = 2.25）到脱水 schoepite（x = 1）的标准摩尔等压热容随含水量的变化在 100 至 500 K 的等温线上基本上呈线性变化。这些发现对层状铀酰腐蚀相和吸湿性材料的脱水具有重要意义。
