D. Viehland et Jf. Li, COMPOSITIONAL INSTABILITY AND THE RESULTANT CHARGE VARIATIONS IN MIXED B-SITE CATION RELAXER FERROELECTRICS, Journal of applied physics, 74(6), 1993, pp. 4121-4124
A phenomenological model has been applied in an attempt to explain the
inability of the ordered regions in the lead magnesium niobate family
of relaxor ferroelectrics to coarsen. This approach is based on the c
oncept that the free energy is lowered by an embryonic decomposition a
long a non-neutral direction. It is proposed that the excess free ener
gy associated with the formation of the non-neutral phase is offset by
the distortability of the perovskite structure toward the pyrochlore.
The lack of coarsening is then explained as a balance of the electros
tatic energy and gradient energy terms, following an earlier published
report. This model is then applied to the La-modified (donor-doped) l
ead magnesium niobate, to explain the dependence of the size of the or
dered regions on the degree of doping as observed by other workers.