Wen Yi, Xu Yun, Brinkman Kyle S, Shuller-Nickles Lindsay
Department of Environmental Engineering and Earth Sciences, Clemson University, Clemson, SC, USA.
Department of Materials Science and Engineering, Clemson University, Clemson, SC, USA.
Sci Rep. 2018 Mar 22;8(1):5003. doi: 10.1038/s41598-018-22982-7.
The titanate-based hollandite structure is proposed as an effective ceramic waste form for Cs-immobilization. In this study, quantum-mechanical calculations were used to quantify the impact of A-site and B-site ordering on the structural stability of hollandite with compositions BaCs(MTi)O, where M = Zn, Ga, and Al. The calculated enthalpy of formation agrees with experimental measurements of related hollandite phases from melt solution calorimetry. Ground state geometry optimizations show that, for intermediate compositions (e.g., CsBaGaTiO), the presence of both Cs and Ba in the A-site tunnels is not energetically favored. However, the decay heat generated during storage of the Cs-containing waste form may overcome the energetics of Ba and Cs mixing in the tunnel structure of hollandite. The ability of the hollandite structure to accommodate the radioparagenesis of Cs to Ba is critical for long term performance of the waste. For the first time, B-site ordering was observed along the tunnel direction ([001] zone axis) for the Ga-hollandite compositions, as well as the intermediate Al-hollandite composition. These compositionally dependent structural features, and associated formation enthalpies, are of importance to the stability and radiation damage tolerance of ceramic waste forms.
基于钛酸盐的钡铁钛矿结构被认为是一种有效的固定铯的陶瓷废物固化体。在本研究中，采用量子力学计算来量化A位和B位有序化对组成为BaCs(MTi)O（其中M = Zn、Ga和Al）的钡铁钛矿结构稳定性的影响。计算得到的生成焓与通过熔体溶液量热法对相关钡铁钛矿相的实验测量结果一致。基态几何结构优化表明，对于中间组成（例如CsBaGaTiO），A位隧道中同时存在Cs和Ba在能量上是不利的。然而，含铯废物固化体储存过程中产生的衰变热可能会克服钡铁钛矿隧道结构中Ba和Cs混合的能量障碍。钡铁钛矿结构容纳铯与钡放射性共生的能力对于废物的长期性能至关重要。首次在Ga - 钡铁钛矿组成以及中间Al - 钡铁钛矿组成中观察到沿隧道方向（[001]区轴）的B位有序化。这些与组成相关的结构特征以及相关的生成焓对于陶瓷废物固化体的稳定性和耐辐射损伤性具有重要意义。
