Abstract: The pyrochlore-free Bi₂O₃ doped lead magnesium niobate ceramics were fabricated through columbite
precursor method and their B-site ordering structures were characterized by XRD and SAED techniques. With the increase of the ratio between
Mg²⁺ and Nb5⁺ cation content, hexagonal Mg₄Nb₉O₆ becomes coexisting with orthorhombic MgNb₂O₆ in the columbite precursor.
The donor doping with Bi³⁺ can compensate for the space charge generated by the nonstoichiometric order and thus promotes the growth
of ordering regions. Moreover, the ordering degree of PMN can be increased pronouncedly with the increase of bismuth cation content
of the specimen. The average size of ordering microdomains estimated in PMN-0.05Bi specimen is about 22nm.

Key words: PMN, ordering microdomains, relaxors, perovskites