Ni-H体系中固溶体的电子结构和热力学

Gavriljuk Vg
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引用次数: 1

摘要

基于第一性原理原子计算和实验x射线衍射数据,讨论了Ni-H体系中广泛存在的氢化镍概念。利用密度泛函理论和Wien2k程序包计算了Ni-H固溶体的总内聚能。它对氢浓度的依赖是线性的,这表明沉淀反应不存在任何能垒。此外,在氢镍比(H/Ni)为0.03 ~ 0.75的范围内,计算得到的溶液焓二阶导数为负,这是旋量分解的标志。这些氢浓度与x射线衍射的测量结果一致,x射线衍射的结果传统上用氢化镍来解释。计算了电子态的密度,其非单调的浓度依赖关系与溶液焓的浓度依赖关系相关联,这也是spinodal分解所期望的。所得结果可以解释为Ni-H体系中具有电子源的独立分解的混相间隙。此外,在H/Ni比约为0.7的含氢镍中,利用力学谱法观察到应变相关的内摩擦。这种效应是由不可逆的塑性变形控制的,这是典型的固溶体,而不是脆性化合物。最后,根据两种吉布类型的沉淀反应,讨论了许多金属中的“氢化物”。关键词:镍,氢,从头计算,旋多分解,氢化物
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Electron structure and thermodynamics of solid solutions in Ni–H system
The widespread concept of nickel hydride in the Ni–H system is discussed based on the first–principle atomic calculations and experimental X–ray diffraction data. The total cohesion energy in Ni–H solid solution has been determined using the density functional theory and program package Wien2k. Its dependence on hydrogen concentration is shown to be linear, which suggests the absence of any energy barrier for precipitation reaction. Moreover, the second derivative of the calculated solution enthalpy is negative within the hydrogen–to–nickel ratios, H/Ni, of 0.03 to 0.75, which is a sign of spinodal decomposition. These hydrogen concentrations are consistent with the measurements of X–ray diffraction, of which results are traditionally interpreted in terms of Ni hydride. The density of electron states has been calculated, and its non–monotonous concentration dependence correlates with that of solution enthalpy, which is also expected for spinodal decomposition. The obtained results are interpreted as miscibility gap in the Ni–H system with spinodal decomposition having the electron origin. In addition, using mechanical spectroscopy, the strain dependent internal friction has been observed in the hydrogen–charged nickel with H/Ni ratio of about 0.7. This effect is controlled by irreversible plastic deformation, which is typical for solid solutions, not for brittle chemical compounds. Finally, the “hydrides” in a number of metals are discussed in terms of two Gibb’s types of precipitation reactions. Keywords: nickel, hydrogen, ab initio calculations, spinodal decomposition, hydride
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