A variety of intermetallic compounds have been irradiated with high energy ions to determine the criteria for an amorphous transformation. Those compounds with limited compositional range or solubility tend to become amorphous during irradiation, whereas those compounds with wide solubility tend to remain crystalline. This solubility criterion is consistent with the concept that a critical defect density which will result in a greater free energy of the crystal phase than the free energy of the amorphous phase is necessary for the amorphous transformation. This critical defect density is lower in those compounds that become amorphous. The ionicity criterion of Naguib and Kelly does not work for these intermetallic compounds, but the temperature criterion is probably valid and is, in fact, directly related to the proposed solubility criterion.

Amorphous phase formation in irradiated intermetallic compounds

The formation of amorphous or crystalline damaged regions by ion bombardment or neutron irradiation of Ge and Si is discussed. Several experiments have demonstrated that Ge and Si become amorphous when bombarded to high fluences with ions of 20–200 keV energy, but remain crystalline after low ion fluences (<1014/cm2) or after fission neutron irradiations up to very high fluences. The present results indicate that a fission neutron fluence of 5 × 1035 n/cm2 at ∼50 °C and at a flux of 6 × 1012 n/cm2/sec produces no amorphism in Ge or Si, but that microcrystals appear after annealing at 450 °C. It is concluded that the individual damaged regions produced by high-energy ions or by primary knock-on atoms from fission neutron collisions are crystalline. When these damaged regions are created rapidly enough so that overlap occurs before appreciable annealing of point defects takes place, the damaged regions become amorphous. The critical defect concentration required for spontaneous transformation to am...

Damaged regions in neutron-irradiated and ion-bombarded Ge and Si

The ordering and disordering of solid solutions under irradiation

Lattice resolution measurement of strain fields at Guinier-Preston zones in Al-3.0% Cu

Amorphization of intermetallic compounds under irradiation - A review

Of particular interest in the study of crystal lattice imperfections are the magnitude and extent of their influence on atornic structure. In the present work two-beam crystal lattice images have been used to examine directly the perturbing influence of Guinier-Preston zones in Al-4% Cu, damaged regions in neutron irradiated Ge and dislocations in deformed and partially crystallized Ge. The 2–02 A; spacing of (200) planes was resolved in Al-4% Cu while the 3–26 A spacing of (111) planes was resolved in the Ge specimens. The crystal lattice images were obtained using a high vacuum, short focal length (2.1 mm) Siemen's Elmiskop 1 operated at 100 kv with pointed filaments and thin film objective apertures. The experimental observations reveal: (1) that the G.P. [1] zones are coherent with the matrix (200) planes and produce an observable tensile distortion out to ∼ 20 A on either side of its centre; (2) that when a damaged region in Ge has a size equal to the foil thickness, then the lattice image d...

Influence of crystalline defects on 2-beam crystal lattice images-Experimental

The behaviour of the ordered alloy Zr3Al has been iavestigated by transmission electron microscopy following ion bombardments at temperatures ranging from 30 to 850 K. The diffraction-contrast features of individual damaged regions produced by low-fluence C+, N+ or Ar+ ions (0·5–2·0 MeV) were examined. Imaging with fundamental reflections revealed strain-contrast images arising from defect clusters which have essentially a spherically symmetrical strain-field and which presumably also encompass disordered regions. Other disordered regions, which were not associated with the defect clusters, were rendered visible due to structure factor contrast by imaging with 110 superlattice reflections. Both types of damaged regions were observed to anneal out in the region 723–848 K. With increasing bombarding ion fluence, Zr3Al gradually disordered and this transition was monitored by assessing the change in the long-range order parameter S. Post-irradiation annealing and high-temperature irradiation experim...

M. H. Rainville

Papers

Influence of crystalline defects on 2-beam crystal lattice images-Experimental

The nature of irradiation-produced damaged regions in ordered Zr3Al