The effect of different tetravalent octahedral‐site substitutions (M 4+ = Zr, Tb, and Ce) on the stability of the 1:1 chemically ordered phase in Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) relaxor ferroelectrics were investigated using X‐ray diffractometry and transmission electron microscopy. In their as‐sintered form, all the samples adopted a phase‐separated microstructure that consisted of nanosized 1:1 ordered domains dispersed in a disordered matrix. However, after annealing at 1250°C for 24 h, a fully 1:1 ordered microstructure with large domains (>100 nm) was stabilized in 10 mol%‐terbium‐doped PMN. No ordered‐domain coarsening was observed in pure or zirconium‐doped PMN, which indicated that the size of the solid‐solution additives was critical to stimulating the growth and stability of the 1:1 order. The observation of complete 1:1 order in the terbium‐doped system supports the “random‐site” model description of the Pb(β′ 1/2 β″ 1/2 )O 3 structure. This model also can be used to explain the insensitivity of the diffuse frequency‐dependent dielectric properties to the size of the chemically ordered domains.
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Akbas et al. (2000) studied this question.
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