| Popis: |
Thin crystals of rutile, brookite, anatase, and cassiterite were irradiated in situ in the transmission electron microscope using 1.0 MeV Kr ions at 50-300 K. Synthetic rutile and natural cassiterite, with 0.1-0.2 wt% impurities, remain crystalline up to a fluence of 5 x 10{sup 15} ions cm{sup -2} without evidence for amorphization at 50 K. Natural brookite and anatase, with 0.3-0.5 wt% impurities, become amorphous at fluences of 8.1 x 10{sup 14} and 2.3 x 10{sup 14} ions cm{sup -2}, respectively. We have also studied two natural rutile samples containing {approx}1.7 and 1.2 wt% impurities. These samples became amorphous at 9.2 x 10{sup 14} and 8.6 x 10{sup 14} ions cm{sup -2} at 50 K, respectively. Further analyses of the fluence-temperature data for natural brookite, rutile, and anatase give critical amorphization temperatures of 168 {+-} 11, 209 {+-} 8, and 242 {+-} 6 K, respectively. Results are briefly discussed with respect to several criteria for radiation resistance, including aspects of the structure, bonding, and energetics of defect formation and migration. |
