Anisotropy of defect creation in electron-irradiated iron crystals

Single crystals of {α}-iron were irradiated perpendicularly to the (100), (110), and (111) planes with electrons in the range 0.35-1.7 MeV and their electrical resistivity change rates were measured. A geometrical model of the threshold-energy surface for atomic displacement in a bcc lattice produces a fit to the experimental data leading to the following values for the threshold energies in the principal crystal directions: Td〈100〉=17±1 eV, Td〈111〉=20±1.5 eV, and Td〈110〉30 eV. The specific resistivity of a Frenkel pair is deduced to ρFFe=(30±5) {μ}{Ω}cm/at.%. From the obtained Td's we derived an interatomic potential of the Born-Mayer type, valid in the range 1.2≤r≤2.5 {}. We propose as a good choice: V(r)=8900e^-4.5r eV. The recovery due to isochronal annealing during stage I, after irradiation at different electron energies, was measured and related to specific recovery mechanisms. Thus, the first important substage, IB ({~} 66 K), is due to the recovery of close Frenkel pairs created in the $〈100〉$ direction, while a comparison of calculated cross sections suggests that IC ({~} 87 K) possibly stems from $〈111〉$ close pairs. Substage ID (90-110 K) is complex; its first part, below 100 K, originates mostly from defects produced in the $〈100〉$ direction and the second part, above 100 K, together with IE, principally originates from defects produced in the $〈111〉$ direction.