International
Tables for Crystallography Volume B Reciprocal space Edited by U. Shmueli © International Union of Crystallography 2010 
International Tables for Crystallography (2010). Vol. B, ch. 2.5, p. 351
Figure 2.5.3.22
M. Tanaka^{f}


Figure 2.5.3.22
Schematic diffraction pattern at the [001] incidence of Sr_{2}Nb_{2}O_{7}. Umweganregung paths a and b via fundamental reflections to the 0001 incommensurate reflection. Large and small spots denote fundamental and incommensurate reflections, respectively. The wave number vector of modulation is k = (½ − δ)a*. 