J. Phys. I France 2 (1992) 537-543
Electron microscopy diffraction contrast in quasicrystals: some rulesMaurice Kléman, Wolfgang Staiger and Dapeng Yu
Université de Paris-Sud, Centre d'Orsay, Laboratoire de Physique des Solides, Bâtiment 510, 91405 Orsay Cedex, France
(Received 10 October 1991, revised 27 January 1992, accepted 19 February 1992)
A number of authors have observed dislocations in icosahedral quasicrystals and advanced some rules to the effect of measuring their Burgers vectors, on the basis of the two-beam method in the kinematical approximation. We first shortly review their results, which state that the determination of the direction of the Burgers vector , ( in I P , in I P ), which has six components, can be suitably simplified if the five necessary extinctions fall into two classes, viz. four so-called `strong extinction conditions' (SEC) , and one so-called `weak extinction condition' (WEC) We then state the relationships between the and the components which result from these conditions. We show that the modulus and sign can be determined without ambiguity by examining two incommensurate non-extinguishing diffractions ( , n integer). Any `perfect' dislocation obeys at least approximately the rules which follow from this analysis. Dislocations which fail to obey them can be `imperfect' dislocations (we define them), whose existence should not be discarded.
© Les Editions de Physique 1992