Dislocation contrast by transmission electron microscopy A method for Burgers vector characterization if the invisibility criterion is not valid

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Abstract
The invisibility criterion for dislocations observed by TEM g · b=0, is strictly valid only for pure screw dislocations or pure edge dislocations if g · b ∧ u = 0. A criterion for quick discrimination between g · b = 0 and g · b ≠ 0 has been established for dislocations lying in an elastically isotropic medium if g · b ∧ u » 0 : on varying the deviation from the exact Bragg position, the dislocation image presents a stationary two-sided contrast if g · b=0; it presents a moving one-sided contrast if g · b ≠ 0. This criterion is used for characterization of Burgers vector of dislocations in feldspars. The validity of the criterion in elastically anisotropic medium is discussed.