EVIDENCE AGAINST AMORPHOUS PHASE FORMATION BY THE SOLID-STATE REACTION OF IRON ON SINGLE-CRYSTAL ZR(0001) IN ULTRAHIGH-VACUUM

Thin polycrystalline Fe-57 films were deposited in ultrahigh vacuum onto a well ordered Zr(0001) single-crystal surface characterized by low-energy electron diffraction and Auger electron spectroscopy, and were investigated in situ by conversion electron Mossbauer spectroscopy (CEMS). In contrast to the case of a polycrystalline triple layer of 1000 angstrom Zr/200 angstrom Fe-57/150 angstrom Zr, the formation of amorphous Fe-Zr was not observed on the ordered single-crystal surface upon annealing at around 660 K. Furthermore, iron-film deposition onto an ion-beam irradiated, damaged Zr(0001) surface held at 660 K during deposition resulted in the formation of intermetallic crystalline Zr3Fe, and not of amorphous Fe-Zr. These results prove that the presence of zirconium grain boundaries is an essential requirement for the nucleation of amorphous Fe-Zr by a solid state reaction. Surface defects at the zirconium surface seem to promote nucleation of the thermodynamically more stable intermetallic compound Zr3Fe.