Structure and thermodynamic properties of zirconium hydrides by structure search method and first principles calculations
Structure and thermodynamic properties of zirconium hydrides by structure search method and first principles calculations
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通过结构搜索方法和第一原理计算研究氢化锆的结构和热力学性质
DOI：
10.1016/j.commatsci.2018.03.066
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发表时间：
2018-07
影响因子：
3.3
通讯作者：
Song Hai Feng
中科院分区：
文献类型：
--
作者：
Zhu Xueyan;Lin De Ye;Fang Jun;Gao Xing Yu;Zhao Ya Fan;Song Hai Feng
压水堆中沉淀锆氢化物的形成与包壳的氢脆密切相关。本文系统地研究了Zr氢化物ZrH x （x= 0.5, 1,1.5, 2）的结构及其热力学性质，并将跳盆算法与第一性原理计算相结合。所有实验鉴定的ZrH x结构都得到了再现，并发现了更稳定的新结构。对于ZrH 0.5，最稳定的结构是Pn 3¯m对称。实验发现的P3m1 ζ-ZrH 0.5在动力学和力学上都是稳定的。澄清了P3m1 ζ-ZrH 0.5的修正晶格常数和原子坐标。对于ZrH，本工作中发现的最稳定的结构是P4 2/mmc对称，这与实验结果一致。对于ZrH 1.5，发现P4 2/nnm结构在低温下最稳定，而实验观察到的p3¯m结构在高温下最稳定。对于ZrH 2， I4/mmm （c/a= 1.25）对称的双稳结构最稳定，这与实验结果一致。通过对Zr氢化物相变过程中Zr基体结构变化的分析，提出以P4 2/nnm ZrH 1.5结构作为反应中间体可以合理解释γ→δ→ε相变。另外，通过对比生成自由能，我们发现δ-ZrH 1.5是高温下最稳定的Zr氢化物，而ε-ZrH 2在低温下最稳定。结果表明，快速冷却有利于δ-ZrH 1.5的形成，缓慢冷却有利于γ-ZrH 1.5的形成。
The formation of precipitated zirconium (Zr) hydrides is closely related to the hydrogen embrittlement of the claddings in pressured water reactors. In this work, we systematically investigated the structures of Zr hydrides ZrH x (x= 0.5, 1, 1.5, 2) and their thermodynamic properties by combining the basin hopping algorithm with first principles calculations. All the experimentally identified structures of ZrH x were reproduced, and new structures that are more stable were found. For ZrH 0.5, the most stable structure is of Pn 3¯ m symmetry. The experimentally discovered P3m1 ζ-ZrH 0.5 was found in this work, which is both dynamically and mechanically stable. The corrected lattice constants and atomic coordinates of the P3m1 ζ-ZrH 0.5 are also clarified. For ZrH, the most stable structure found in this work is of P4 2/mmc symmetry, which is in agreement with experiments. For ZrH 1.5, it was found that the P4 2/nnm structure is most stable at low temperature, while the experimentally observed Pn 3¯ m structure is most stable at high temperature. For ZrH 2, the bistable structures of I4/mmm (c/a= 1.25) symmetry is most stable, which is consistent with experiments. Furthermore, through analysis of the structural changes of Zr matrixes companying the phase transitions of Zr hydrides, we suggest that γ→ δ→ ε phase transitions can be explained reasonably using the P4 2/nnm ZrH 1.5 structure as the reaction intermediate. Additionally, through comparing the formation free energy, we found that δ-ZrH 1.5 is the most stable Zr hydride at high temperature, while ε-ZrH 2 is most stable at low temperature. Our results indicate that fast cooling process will promote the formation of δ-ZrH 1.5, and slow cooling process will promote the formation of γ-ZrH.
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