Abstract: (1-x)PNN-xPT(x=0.30～0.40) ceramics were prepared by a two-steps synthesis method. Phase structure and dielectric properties were studied.
Morphotropic phase boundary exists in (1-x)PNN-xPT system at about x=0.34～0.38 composition range according to XRD analysis. Dielectric properties
measurments showed that the optimum value of dielectric constant was obtained and the phenomenon of dielectric dual peaks was found for composition near the
morphotropic phase boundary. One dielectric peak is phase transition peak from relaxor ferroelectric phase to paraelectric phase. The other peak lying in 130～150℃ temperature range results from relaxational polarization
of the valence change of Ni ion and kinds of defects in (1-x)PNN-xPT system.

Key words: lead nickle niobate, morphotropic phase boundary, dielectric properties, dielectric dual peaks, relaxational polarization