高压下面心立方CeH_(9)和CeH_(10)动力学性质的第一性原理研究

First-Principles Study of the Dynamics in Face-Centered Cubic CeH_(9) and CeH_(10) under High Pressure

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CeH_(9)和CeH_(10)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CeH_(9)和CeH_(10)不具有显著的质子扩散,但1 500 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) cm^(2)/s和1.9×10^(-4)~1.5×10^(-4) cm^(2)/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。

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 CeH_(9) and CeH_(10) 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,CeH_(9) and CeH_(10) do not have significant proton diffusion at room temperature,but fully transform into the superionic state at 1 500 K with diffusion coefficients of 1.6×10^(-4)-1.2×10^(-4)cm^(2)/s and 1.9×10^(-4)-1.5×10^(-4) cm^(2)/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.