Role of atomic bonding for compound and glass formation in Ni-Si, Pd-Si, and Ni-B systems

Valence electronic structures of crystalline compounds and glassy alloys of Ni silicides, Pd silicides, and Ni borides are studied by soft-x-ray spectroscopy over wide ranges of Si and B concentrations. The samples prepared include bulk compounds, glassy ribbons, and amorphous sputtered films. Silicon K{β} emissions of Ni and Pd silicides generally consist of a prominent peak fixed at {}4.5 and {}5.8 eV below the Fermi level EF, respectively, with a shoulder near EF which grows and shifts toward lower energy with increasing Si concentration. The former is identified as due to Si p--like states forming Si 3p--Ni 3d or Si 3p--Pd 4d bonding states while the latter as due to the corresponding antibonding states. Ni L₃ and Pd L₃ emissions of these silicides indicate that Ni 3d and Pd 4d states lie between the above two states. These local electronic configurations are consistent with partial-density-of-states (PDOS) calculations performed by Bisi and Calandra. Similar electronic configurations are suggested for Ni borides from B K{α} and Ni L₃ emissions. Differences of emission spectra between compounds and glasses of similar compositions are rather small, but some enhancement of the contribution of antibonding states to the PDOS near EF is suggested for certain glasses over that of the corresponding compounds. These features are discussed in connection with the compound stability and glass formability.