Formation of transition metal silicides by solid–gas reactions: thermodynamic and kinetic considerations

Alternative synthesis routes to nickel silicides are discussed. Results of the reactions of Ni with a SiCl4/H2 gas mixture (1), of NiSi with NiCl2 (2) as well as of Si with nickel halides (3) are presented. Kinetics of the reactions (1) and (2) were studied in detail by in situ electrical resistance measurements and isothermal X-ray powder diffraction, respectively. Kinetic evaluation of the electrical resistance measurement data points to island and layered silicide growth in process (1). XRD data analysis leads to the conclusion that process (2) proceeds via transient metastable nickel silicide phases, which are interrelated with the thermodynamically stable silicide phases Ni2Si, Ni3Si2 and NiSi.