First-Principles Study of the Dynamics in Face-Centered Cubic CeH9 and CeH10 under High Pressure
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摘要: 高压下的稀土金属超氢化物因具有高温超导电性而受到广泛关注。由于实验只能部分地确定超氢化物中稀土金属原子的晶格结构，因此，第一性原理计算成为全面理解其结构与物性的重要方法。基于第一性原理计算，对氢含量不同但Ce晶格结构相同的面心立方CeH9和CeH10的弹性、晶格动力学、质子动力学性质进行了对比研究，发现低氢含量有利于面心立方超氢化铈的弹性和声子稳定向低压拓展。在100～140 GPa压强区间，室温下CeH9和CeH10不具有显著的质子扩散，但1500 K时全面转变为超离子态，扩散系数分别为1.6×10−4～1.2×10−4 cm2/s和1.9×10−4～1.5×10−4 cm2/s；扩散系数与温度、氢含量正相关，但与压强负相关。所获得的压强、温度及氢含量对超氢化铈结构与动力学性质的影响规律可为其他超氢化物研究提供参考。Abstract: Rare-earth metal superhydrides have attracted much attention because of their high-temperature superconductivity. Since experimental measurements can only determine the structures of rare-earth metal atoms in the superhydrides, first-principles calculations have become an important complementary method for a comprehensive understanding on their structures and physical properties. In this work, the elasticity, lattice dynamics and proton dynamics properties of face-centered cubic CeH9 and CeH10 with different hydrogen contents but the same Ce lattice structure are investigated comparatively by first-principles calculations. The low hydrogen content is found to favor the elastic and phonon stabilization of face-centered cubic cerium superhydrides expanding to low pressures. At 100–140 GPa, CeH9 and CeH10 do not have significant proton diffusion at room temperature, but fully transform into the superionic state at 1500 K with diffusion coefficients of 1.6×10−4−1.2×10−4 cm2/s and 1.9×10−4−1.5×10−4 cm2/s; the diffusion coefficient is positively correlated with temperature and hydrogen content, but negatively correlated with pressure. The findings on the laws of pressure, temperature and hydrogen content affecting the structure and dynamics of cerium superhydrides are obtained, which can be used as a reference for the study of other superhydrides.
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Key words:
- high pressure /
- superhydrides /
- dynamics /
- superionic states /
- first-principles
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图 4 CeH9和CeH10的部分径向分布函数
Figure 4. Partial radial distribution function of CeH9 and CeH10
表 1 高压下CeH9和CeH10的弹性常数和弹性模量的变化
Table 1. Elastic constants and elastic modulus change of CeH9和CeH10 with pressure
CeHx Pressure/GPa C11/GPa C12/GPa C44/GPa (C11−C12)/GPa (C11+2C12)/GPa B/GPa G/GPa CeH9 80 726 89 134 637 904 301 191 100 818 102 173 716 1022 341 232 120 904 116 194 788 1136 379 259 140 983 132 209 851 1247 415 279 160 1056 149 221 907 1354 451 296 180 1124 167 230 957 1458 486 310 CeH10 80 673 106 −407 567 885 100 759 122 227 637 1003 335 260 120 841 138 274 703 1117 372 303 140 922 153 309 769 1228 410 337 160 998 169 339 829 1336 445 367 180 1072 185 365 887 1442 481 395 
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