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5.1.4.2 Lattice Imaging of D022 and Dla Phases


 The lattice imaging technique is well established and

will not be reviewed here. An excellent review has been

prepared by Sinclair (1979). Briefly, all the information

contained in a lattice image is in the diffraction pattern

from which the lattice image is produced. The advantage

of the lattice image over the diffraction pattern is the

significantly better spatial resolution in a lattice image

compared to a diffraction pattern. There are exceptions

to this, of course. If a focused electron probe is used

to form a diffraction pattern, the diffracting volume will

be on the order of the probe size which can sometimes

approach lattice dimensions.

 The D022 and Dla phases do not present major

difficulties for lattice imaging. From Figures 2.20b and

2.20c, it should be clear that the simplest image can be

formed with the 1/4(420) and 1/5(420) reflections. These

represent real lattice spacings of 3.18 Angstroms and 3.98

Angstroms, respectively. Figure 5.12 is a lattice image

of both the Dla and D022 phases using the 1/4(420) and

1/5(420) reflections from a B = [001] zone axis under

axial illumination conditions. The inset describes this

imaging condition. The large lattice spacings are about

3.9 Angstroms. Next to these are lattice planes of 3.2

Angstroms spacing. The former corresponds to Ni4Mo