Nanometer-range atomic order directly recovered from resonant diffuse scattering

Determination of chemical ordering in the complex perovskite Pb(Cd1/3Nb2/3)O3

“…The chemically ordered region sizes in PMN are found to be larger than those in PNN (Dmowski et al, 2002). The superlattice diffraction spots in PZN are broad and of small intensity, which is similar to PMN (Paściak et al, 2013;Kopecký et al, 2016). It is shown from this work that PMN and PZN exhibit a lower degree of chemical ordering than PCN, which has a fully ordered chemical distribution.…”

“…Thus, the surrounding matrix must be Nb-rich in order to reach the overall 2:1 ratio given by the stoichiometry and electrical charge balance. This model was named -COR in recent years (Kopecký et al, 2016). But later, TEM and neutron diffraction on Zr/La-doped Pb(Mg 1/3 -Ta 2/3 )O 3 (PMT) samples, as well as atomic resolution Z-contrast imaging on PMN (Akbas & Davies, 1997Dmowski et al, 2002;Cantoni et al, 2004;Montgomery et al, 1999;Yan et al, 1998;Jin et al, 2001), showed that in the ordered region Ta 5+ (Nb 5+ ) occupied the B 00 site, while Mg 2+ and Ta 5+ (Nb 5+ ) occupied the B 0 site randomly with a 2:1 ratio.…”

Atomic-resolution electron microscopy of nanoscale local structure in lead-based relaxor ferroelectrics

“…While X-ray and neutron scattering are the predominate characterization methods used to explain these details, making direct connections between composition, structure, and polarization have proven exceedingly difficult [11][12][13][14][15][16][17] . For example, while nanoscale chemical ordering of the B sub-lattice cations was one of the first signatures revealed 17,18 and is found to varying degrees in all Pb-based relaxor ferroelectrics 19,20 , its details are still being explored [21][22][23] .…”

Relaxor Ferroelectrics: Back to the Single-Soft-Mode Picture

“…This F 2g mode is actually an acousticlike mode folded from the Brillouin zone corner of the parent Pm3m (Z ¼ 1) structure, what explains its temperature stability and rather low frequency. However, in the presence of considerable B-site occupational fluctuations [56], it is reasonable to assume that the Fm3m (Z ¼ 2) symmetry is strongly perturbed and many other modes from the flat part of the acoustic phonon branches near the Brillouin zone boundary are contributing to this Raman band. This disorder also allows for the bilinear coupling between the two bare modes of intrinsically different symmetry.…”