Electron spectroscopy on metallic glasses

Abstract

With 36 FiguresThis chapter will deal with electron spectroscopy measurements on metallic glasses. The most important aim of these experiments is to get detailed information about the electronic structure of the solid to be studied. Since many physical properties like electronic specific heat, magnetic susceptibility, ferromagnetism, superconductivity and thermodynamic data are directly related to the electronic structure of a solid, the importance of electron spectroscopy measurements is evident. OverviewBeside the usual questions which can be investigated on crystalline alloys, additional interesting issues related to the electronic structure of glassy alloys arise: (i) Do the alloys which are good glass formers (alloys which can be obtained in the amorphous phase by rapid quenching from the melt by low cooling rates and which have hi#h crystallization temperatures) have any common electronic properties? (ii) Are there any correlation between parameters which define the glassy state (e.g., glass and crystallization temperature, lowest required cooling rate, reduced glass temperature Trg= TJT m where Tg and T m are the glass and melting temperatures, respectively) and electronic properties ? The former question is related to the model of Nagel and Tauc [9.1] which treats the glass as a nearly-free-electron metal. They found that there will be increased stability against crystallization when the Fermi level E v is located at a minimum in the density of states.Therefore, the metallic glasses offer the opportunity to study new and interesting problems besides the standard questions to be solved in investigations on crystalline alloys. In addition, they make it possible to study alloys in continuous ranges of concentrations and at concentrations at which no crystalline phase exists.The significance of electron spectroscopy in studying the electronic structure of alloys and the progress in preparing new metallic glasses has stimulated many workers to perform measurements in this field. A summary of the papers published so far is given in Table 9.1. Besides the alloys studied by el6ctron spectroscopy, the different kind of experiments and excitation energies are listed 284 P. Oelhafen in the following columns. As can be seen from the second column, most of the alloys fall into two groups : the transition-transition metal ~ alloys (T-T group) and alloys containing (at least) one transition metal and a normal metal (nontransition or rare-earth metal) or metalloid (T-N group). From all the studies given in Table 9.1, a fairly precise picture of the electronic structure of metallic glasses emerges. Even though electron spectroscopy measurements can yield information on both surface and bulk properties of a solid (the escape depth of the electrons to be detected in these experiments is between 5 and 30 A, depending on their energies), in most of the experiments done so far the bulk properties have been studied. However, there are many interesting phenomena related to the surface properties of glassy alloys, like corros...

Electronic structure of liquid transition metals studied by time resolved photoelectron spectroscopy

“…Regarding the distinct changes in the valence band spectra of Mo and W on melting we suggest marked changes in the atomic short range order since we can exclude strong influences from a change in the photoemission process itself as in the case of Pd. As it turned out in earlier investigations on binary amorphous transition metal alloys [26,31] the valence band spectra are best described by calculations for the fcc structure which did yield much better agreement than the bcc structure. Since the atomic structure of amorphous and liquid alloys are rather similar [11,32] it is tempting to adopt the model of an fcc-like short range order for the liquid phases of Nb, Mo, Ta and W. Within this model the coordination number would be markedly increased on melting and the atomic short range order is fcc-like.…”