DISPLACEMENT FUNCTIONS FOR DIATOMIC MATERIALS

We have used an extension of the methods of Lindhard et al. to calculate the total displacement function ηij(E) for a number of diatomic materials, where nij(E) is defined to be the average number of atoms of type-j which are displaced from their sites in a displacement cascade initiated by a PKA of type-i and energy E. From the nij(E) one can calculate the fraction ηij(E) of the type-j displacements produced by a type-i PKA with energy E. Values of the ηij for MgO, CaO, A12O3, and TaO are presented. It is shown that for diatomic materials with mass ratios reasonably near one (e.g., MgO, Al2O3) and equal displacement thresholds for the two species the ηij become independent of the PKA type i at energies only a few times threshold. However, for larger mass ratios the ηij do not become independent of i until much larger energies are reached - e.g. > 105 eV for TaO. In addition, it is found that the ηij depend sensitively on the displacement thresholds, with very dramatic changes occuring when the two thresholds become significantly different from one another. © 1979.