Interpretation of HRTEM images of partially amorphized pyrochlore structure types

摘要

Results of image simulations on partially amorphous microlite (Ca(sub 2)Ta(sub 2)O(sub 7), pyrochlore structure) are presented. Results indicate that HRTEM images are not sensitive to position of amorphous layers within a crystalline matrix. It is also observed that the limit of detection of amorphous material within a crystalline matrix is dependent on total thickness. In thin crystals (<150(Angstrom)), up to 75 vol% crystalline material can give rise to aperiodic images, yet addition of a small amount of crystalline material (80 vol% crystalline) produces a periodic image. Images calculated for isolated spheres of amorphous material distributed within crystalline microlite suggest that isolated domains of amorphization are observable at sample thicknesses less than 3x the diameter of the feature. Image contrast of amorphized domains is enhanced by imaging at defocus settings significantly different than Scherzer focus. This indicate that interpretation of HRTEM images of partially amorphized crystalline materials should be undertaken with caution, and estimates of the volume of damage considered only qualitative.