Structure of the 〈0110〉 dislocation in sapphire

Experimental evidence of the existence of 〈010〉 dislocations in the {2 0} prism planes in sapphire has been obtained by transmission electron microscopy. By the weak-beam technique it has been shown that the 〈010〉 dislocations may dissociate into three partials. The partials all have a Burgers vector of ⅓ 〈010〉 and are separated by two identical faults. The distance between two partials is in the range 75-135 Å, corresponding to a fault energy of 320±60 mJ/m2. Perfect 〈010〉 dislocations have also been observed. These dislocations exhibited either one or two peaks when imaged in the (030) reflection by the weak-beam technique. The interpretation of the electron micrographs has been supported by computer simulation of the dislocation images. A faulted dipole has been observed, indicating that some of the prismatic loops often seen to lie in rows along [0001] are faulted with a ⅓ 〈010〉 Burgers vector. A mechanism for the dipole formation is suggested.