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Abstract
A systematic study of the temperature dependence of the superlattice reflections has been carried out using anomalous x-ray scattering technique in a single crystal Pb(Mg⅓Nb⅔)O3 (PMN). Two types of nanodomains were found to exist in PMN: a) chemically ordered nanodomains, and b) polar regions formed by short-range correlated ionic displacements. Each type of nanodomains gives rise to superlattice reflections at different locations in the reciprocal space. From the temperature dependence of the superlattice peaks, corresponding to polar nanodomains, we found a second order structural phase transition near Tf=220 K. This transition corresponds to the freezing of correlated oxygen octahedra rotations with temperature-independent correlation radius of 40 Å below Tf. Chemical nanodomains due to short-range order on the B sites were shown to exhibit isotropic shape and temperature independent size of 50 Å in 15–800 K interval. Anomalous diffraction near Pb LIII absorption edge has shown that Pb displacements are not random at low temperatures, but correlated on the short-range scale.
