The 2D through
space homonuclear correlation RFDR sequence has been used to
investigate the spatial proximity between the different phosphorous
sites. Since the dipolar interaction is distance dependent (~1/r3),
correlation signals can only be created between spatially close
phosphorous sites belonging to the same micro-crystallite and thus
to the same phase. All the phosphorous sites of a given phase correlate
all together, creating thus a set of off-diagonal signals, whereas the
lack of signal indicates that the phosphorous sites belong to different
phases.