WEAK-BEAM STUDY OF ANTIPHASE BOUNDARIES IN FE-27-PERCENT-AL AS A FUNCTION OF TEMPERATURE

The study by electron microscopy of the fringes due to planar defects such as antiphase boundaries (APB) is riot a new problem, and the equa tions describing this phenomenon are well-known, but the effect on ele ctron diffraction of the broadening with temperature of these boundari es close to order-disorder transitions is a new field of investigation . We show hem that a careful study of the behaviour of the fringes gen erated by the APB in dark field images is a good method to analyze the different order-disorder transitions. In particular we describe in de tail a quantitative method that allows us to determine the correlation length xi below a second order transition.