Direct Imaging of Atomic Ordering in Undoped and La‐Doped Pb(Mg 1/3 Nb 2/3 )O 3

In this paper, we report the first direct observations of local ordering in undoped and La‐doped Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) on an atomic scale by high‐resolution (∼1.26 Å) Z ‐contrast imaging. The 1:1 ordering occurs by a variation in the occupancy of Mg and Nb cations between B I and B II sublattices. In ordered regions, the B II sublattice is dominantly occupied by Nb cations, but a small Mg occupancy cannot be excluded. The Mg cations were found to dominantly occupy the B I sublattice. Within the B I sublattice, the local Mg/Nb ratio was found to vary among the various B I sublattices. The results show that the random‐site model, rather than the space‐charge model, is a better structural model for the 1:1 ordering observed in PMN. A random distribution of Mg and Nb cations on the B I sublattice within 1:1 ordered regions is believed to be responsible for the relaxor behavior of mixed B‐site cation relaxors, such as PMN.