1ST OBSERVATION OF AMORPHIZATION-J IN SINGLE-CRYSTAL MGAL2O4 SPINEL

We have observed the amorphization of single-crystal MgAl2O4 spinel induced by 400 keV Xe2+-ion irradiation at 100 K to a peak damage level of 25 displacements per atom (dpa). Rutherford backscattering spectrometry combined with ion channelling showed that the amount of radiation damage accumulated with increasing dose and reached a fully random level at a dose of 1 X 10(16) Xe cm-2. Cross-sectional transmission electron microscopy examination of the high-dose sample revealed the presence of a continuous amorphous layer of about 130 nm, followed by a radiation-damaged but crystalline transition layer on the undamaged spinel substrate. The irradiation-damaged crystalline layer is highly defected, and electron diffraction from this region exhibits a decrease in or complete loss of intensity at the spinel (220) reciprocal-lattice positions. These observations suggest that the principal driving force in the amorphization of MgAl2O4 spinel is through the accumulation of chemical disorder (antisite defects) and dislocations (line defects). This is the first experiment where amorphization of spinel is demonstrated. In previous irradiation studies of spinel at elevated temperatures (300-1100 K) up to 250 dpa, no amorphization has ever been observed.