OPTICAL CHARACTERIZATION OF CRYSTAL DISLOCATIONS - THE CASE OF BISMUTH-GERMANATE

Dislocations in Bi4(GeO4)3 single crystals were characterized by several optical methods: (i) Chemical etching followed by etch pit examination using optical microscopy. (ii) Stress birefringence microscopy, a method that reveals the anisotropy of the stress field around dislocations. For dislocations viewed end-on, the sign of the edge component has been determined by a simple procedure involving external compression of the crystal. Birefringence images of dislocations viewed side-on are only obtained when the Burgers vector has an edge component parallel to the direction of observation. (iii) Parallel beam, Schlieren and phase contrast microscopy, combined with analog contrast enhancement. By these techniques the field of mass densities around the dislocations is observed. (iv) Dark field microscopy to detect the inclusion strings that might decorate dislocations. © 1990.