Hydrogen conduction-electron density

The incompletely filled 4f-shell confers a magnetic moment to the lanthanide ions and it is the Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism via polarization of the conduction electrons which is responsible for the occurrence of long-range ordered magnetic structures in the lanthanide metals. Details can be foimd in numerous reviews, among others in vol. 1, chs. 3, 6 and 7 (1978) of this Handbook series and a recent one by Jensen and Mackintosh (1991). The addition of hydrogen, both in solution or resulting in hydride formation, leads to a decrease of the conduction electron density e (cf. sect. 5)... 

In metals, the conduction electrons are delocalized in the whole crystal, and consequently, the H+ neighborhood results in the electron density of the conduction band [31,33], Then, hydrogen in metals and small band gap semiconductors exist as a screened proton [9], As a result, it is possible that the proton could have a high coordination number, and can be interstitially located in tetrahedral and/or octahedral sites [32],... 

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