Abstract: The studies of initial calcining reactions of MgNb₂O₆were carried out at different calcining temperatures.
The results show that the amount of free MgO exhibits a decreasing with the increase of MgNb₂O₆ calcining temperature. PMN based electrostrictive
ceramics were prepared according to the process described by Swartz et al, but MgNb₂O₆ was formed without addition of excess MgO at 1050℃.
No pyrochlor phase, within the detection limits of X-ray diffractometer was observed in the PMN based ceramics. At room temperature the
longitudinal electrostrictive strain (S₁₁) for the ceramics was found to be 1.05×10^-3 with only 6.8% hysteresis applied a quasi-static electric
field 1kV/mm operating frequencies of 0.07Hz.

The relation between calcining temperature of MgNb₂O₆ and electrostrictive properties of the PMN based ceramics was also studied. It
was obvious that Curie temperature T_c of the PMN based ceramics increases with the increase of calcining temperature of MgNb₂O₆ and causes
the ceramics having lower dielectric constant and larger electric machanical hysteresis.

Key words: magnesium niobate, calcining temperature, exess magresium, pyrochlor phase, electrostriction