On the electronic structure of interstitial transition-metal based alloys with boron and carbon impurities

Abstract

Experimental results so far obtained are given for the interstitial solid solutions of boron and carbon in the f.c.c. transition metals and alloys, Ni, Co, Ni_1-xFe_x alloys with × < 0-65, Pd and Pt. First their crystallographic properties are investigated: the conditions and limits of boron and carbon solubility, the increases in the lattice parameter, and the localization of carbon in the sites of the f.c.c. lattice are described. The second part reports the investigation of their physical properties in order to obtain information about the nature, the form and the extension of the screening around the interstitial atom. For this, the transport properties (resistivity and thermoelectric power), the magnetic properties (magnetization, susceptibility and Curie temperature), and the nuclear magnetic resonance of ⁵⁹Co are studied. It is found that the electronic structure of interstitial alloys essentially depends upon whether the matrix is a strong ferromagnet, or a weak ferromagnet or paramagnet. In the first case, the results for C in Ni, Co and Ni_1-xFe_x alloys (x≤0-4) can be interpreted in terms of a large increase of the density of states at the Fermi level, similar to that observed in substitutional Ni or Co based alloys which have a virtual bound state. In the second case (Pd B, Pd C, Pt B and (Ni,_1-x Fe _x) C for × > 0·4), the variation of the density of states due to the interstitial atom is negative, and more negative the higher the interstitial valence number.