无序钯-金合金中氢的光学振动
Optical vibrations of hydrogen in disordered palladium-gold alloys
摘要：
在Pd的fcc晶格中，氢占据具有立方对称性的八面体间隙位置。因此，人们可以预期，在稀固体H溶液中的Pd的光学H振动的基本频带应减少到一个狭窄的3倍简并，非相互作用的各向同性本地振荡器线。由于PdH $_x$溶液在低温下的极限氢浓度非常小（x <0.001），因此用非弹性中子散射来检验这一假设的一些尝试给出了模棱两可的结果。我们增加了最大x合金钯与20原子%的金，并研究了无序的Pd $_{0.8}$金$_{0.2}$ H $_{x}$溶液的浓度从x = 0.03到0.74。根据已报道的$^{197}$ Au穆斯堡尔研究，在x <（0.8）^{6}= 0.26的Pd $_{0.8}$ Au $_{0.2}$ H $_{x}$溶液中的氢原子只能占据没有Au邻居的间隙。这减弱了在较低H浓度的溶液中H-Au相互作用的影响，并有效地防止了低温下的氢聚集。我们的INS研究表明，在浓缩和稀释的Pd $_{0.8}$ Au $_{0.2}$ H $_{x}$解决方案的基本光学H带包括一个尖锐的峰值与宽肩向更高的能量。肩没有显示出随着H浓度降低而消失的趋势，并且在所有研究的样品中主峰的积分强度约为0.44。因此，在Pd中无限稀释的H溶液中的光学带也应该由具有明显肩的峰组成。本文考虑了氢在Pd中溶解度的同位素效应的影响。
英文摘要：
In the fcc lattice of Pd, hydrogen occupies octahedral interstitial positions with cubic symmetry. One could therefore expect that in dilute solid H solutions in Pd the fundamental band of optical H vibrations should be reduced to a narrow line of 3-fold degenerate, non-interacting isotropic local oscillators. A few attempts to test this assumption by inelastic neutron scattering gave ambiguous results due to the very small limiting hydrogen concentration, x<0.001, of the PdH$_x$ solutions at low temperatures. We increased maximum x by alloying Pd with 20 at% Au and studied disordered Pd$_{0.8}$Au$_{0.2}$H$_{x}$ solutions with concentrations varying from x = 0.03 to 0.74. According to reported $^{197}$Au Mossbauer studies, hydrogen atoms in the Pd$_{0.8}$Au$_{0.2}$H$_{x}$ solutions with x < (0.8)^{6} = 0.26 can only occupy interstices having no Au neighbours. This abates the effect of H-Au interactions in the solutions with lower H concentrations and effectively prevents hydrogen clustering at low temperatures. Our INS investigation showed that the fundamental optical H band in both concentrated and dilute Pd$_{0.8}$Au$_{0.2}$H$_{x}$ solutions consists of a sharp peak with a broad shoulder towards higher energies. The shoulder shows no tendency to vanish with decreasing H concentration and amounts to approximately 0.44 integral intensity of the main peak in all studied samples. The optical band in infinitely diluted H solutions in Pd should therefore consist of a peak with a pronounced shoulder too. Implications for the isotopic effects in the hydrogen solubility in Pd are considered in the present paper.
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