Anisotropy of the displacement energy in single crystals of molybdenum

Abstract

Abstract A “geometrical” model for the threshold cnergy surfaceof a b.c.c. lattice is applied to analyse recent measurements of the resistivity change rates in electron-irradiated monocrystalline molybdenum specimens with the orientations [100], [11O], [111] and [112]. Cross sections computed with this surface were matched to the experimental data using various sets of threshold energies as parameters. The best fit was obtained with Td [100] = (35+2 −2) eV, Td [1101 > 2Td [100], Td [111] = (45 f 3) eV. When corn ared to the experimental damage rates the absolute values for the cross sections yield a Frenkel pair resistivity pio = (13 f 2) pfl cm/at.% F.P. Expressions for the energy necessary to penetrate the potential barriers in the principal crystallographic directions are derived and compared to the id[iik] obtained before, with the interatomic potential as parameter. Taking into account the length of the [111] collision chains and the size of the spontaneous recombination volume, the appropriate potential can be chosen in the range between UMo(r)/eV = 3000 exp(−3.2 r/A) and 11,000 exp(−3.8 r/A). An analysis of the displacement cross sections permitted to explain the energy and orientation dependence of stage I recovery and to attribute the sub-stages a t 15 K and 40 K to the annealing o f interstitials due to [100] displacements and the substages between 20 and 33 K to that of [111] chains of various lengths.