Hj. Maier et al., ON THE UNIQUE EVALUATION OF LOCAL LATTICE-PARAMETERS BY CONVERGENT-BEAM ELECTRON-DIFFRACTION, Philosophical magazine. A. Physics of condensed matter. Structure, defects and mechanical properties, 74(1), 1996, pp. 23-43
We summarize some practical aspects of using convergent-beam electron
diffraction (CBED) patterns for determination of three-dimensional lat
tice parameters in crystalline materials. Owing to the insensitivities
of certain lattice spacings to changes in lattice parameters, and to
measurement errors imposed by finite higher-order Laue zone (HOLZ) lin
ewidths, most CBED patterns can be simulated by a number of different
lattice parameter combinations. Unique combinations are found by fitti
ng several patterns obtained from the same area. In cases where a uniq
ue set of all six parameters cannot be found, semiquantitative informa
tion about elastic stress and strain states can still be extracted. Th
e number of obtainable lattice parameters is affected by the symmetry
of the pattern and by the specific HOLZ reflections which are present,
for a given accelerating voltage. Symmetry-breaking distortions in pa
tterns from nominally orthorhombic systems can often be attributed to
deviations in lattice angles as small as 0.01-0.02 degrees away from 9
0 degrees, even if such angular distortions are not expected from know
ledge of the material's bulk behaviour. The correct simulation of CBED
patterns further requires consideration of foil thinning artefacts on
HOLZ line positions. We show that an intelligent choice of zone axis
can provide useful information even from difficult sample geometries.