Abstract
In this paper, we report the first direct observations of local ordering in undoped and La‐doped Pb(Mg1/3Nb2/3)O3 (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 BI and BII sublattices. In ordered regions, the BII sublattice is dominantly occupied by Nb cations, but a small Mg occupancy cannot be excluded. The Mg cations were found to dominantly occupy the BI sublattice. Within the BI sublattice, the local Mg/Nb ratio was found to vary among the various BI 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 BI sublattice within 1:1 ordered regions is believed to be responsible for the relaxor behavior of mixed B‐site cation relaxors, such as PMN.
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