International
Tables for
Crystallography
Volume B
Reciprocal space
Edited by U. Shmueli

International Tables for Crystallography (2010). Vol. B, ch. 2.5, p. 351   | 1 | 2 |

Figure 2.5.3.23 

M. Tanakaf
[Figure 2.5.3.23]
Figure 2.5.3.23

Diffraction pattern of Sr2Nb2O7 taken with [001] incidence at 60 kV. (a) Spot diffraction pattern. Kinematically forbidden 0001 and [200\bar 1] incommensurate reflections exhibit definite intensity. (b) Zone-axis CBED pattern showing dynamical absence of 0001 and [200\bar 1] incommensurate reflections. (c) CBED pattern taken at an incidence with a small tilt from the zone axis to the b* direction. The kinematically forbidden incommensurate reflections have intensity due to incomplete cancellation of two waves through the Umweganregung paths. The wave number vector of modulation is k = (½ − δ)a*.