Observation of dislocations in large crystals of Gadolinium Gallium Garnet

Abstract

Dislocations in very large (ca. 20 cm³) crystals of Gadolinium Gallium Garnet (Gd₃Ga₅O₁₂ or GGG) have been observed by stress induced birefringence and by the decoration method. Both of these techniques can be used to observe dislocations without image magnification. Birefringence has the advantage that precipitates are not required and that the direction and sign of the Burgers vectors of dislocations can be obtained. The decoration method can be used to construct stereo-images of the dislocation lines. Dislocations have been traced from a free surface to regions over 3 cm from this surface by both methods, and it would not have been difficult to observe dislocations at even greater depths than this