Research Abstract
Platinum single crystals were irradiated with fast electrons along various crystallographic directions to determine the ani-sotropy of the damage rate by resistivity measurements. The temperature dependence of the anisotropy was obtained by varying the irradiation temperature from 4.5 K to 40 K and 400 K. The results were interpreted in terms of an anisotropy of the threshold energy for atomic displacement. The evaluation was done by a computer program which fitted a threshold energy profile to the measured damage rates. The effect of details of the threshold energy profile and the effect of electron beam spreading on the anisotropy of the damage rate was studied. Two models, which may explain qualita- tively the effect of temperature on the defect production pro- cess, are discussed. The important results of this work are:
The anisotropy of the damage rate in platinum increases with increasing temperature.
Fitting of the damage rate data by a threshold energy pro-file gives:
a) Zones of minimum threshold energy are around the and 100> direction, while the maximum threshold energy is found around the direction 111 >.
b) with increasing temperature the area of the zones with small threshold energy around the close-packed directions
and 100> decrease.
3.)The increasing anisotropy of the threshold energy with temperature is explained by two mechanisms:
a) The change in the defect pattern between 4.5 K and 40 K due to the instability of close pairs.
b) The defocusing of replacement sequences by thermal lattice vibration.
4.) No safe statements about the temperature dependence of the minimum and the average displacement energy are possible.
Research Journal
Juelich Report, Juel-spez-38, KFA Juelich, W. Germany
