164
and are reproducible to .1 mm. The accuracy in absolute
lattice parameter measurement is very poor, as previously
explained in Chapter 4. No absolute measurement was
attempted. The relative differences in lattice parameter
as measured with CBED between the RSR 197 and RSR 209 is
on the order of .3%. This number compares very favorably
with the x-ray diffraction results of the previous
section.
Not all the CBED patterns from the gamma prime phase
were as symmetrical as those shown in Figure 4.9. Figure
4.1, for example, shows an asymmetrical pattern from the
gamma prime. The origin of the assymetry is unclear.
Measurements from the gamma phase were extremely
difficult to make. Figure 5.30b is a low camera length
B=\114^> CBED pattern from the gamma phase of RSR 185.
Figure 5.30a shows the detail in the central spot.
Figure 5.30b shows both a lack of any {llO} superlattice
reflections in the zero order zone, and no superlattice
FOLZ lines. The pattern is thus clearly from the gamma
phase only. The fine structure in 5.30a shows that the
lattice parameter of the gamma is greater than the lattice
parameter of the gamma prime. There is no perceptible
distortion or loss of symmetry in this gamma B = ,\114/>
CBED pattern. This implies that there is no measurable
strain unless that strain is parallel to the beam.