  This letter reports microwave dielectric measurements performed in the
antiferroelectric phase of NaNbO3 ceramics from 100 to 450 K. Remarkable
dielectric relaxations were found within the antiferroelectric phase and in the
vicinity of ferroelectric-antiferroelectric phase transition. Such dielectric
relaxation process was associated with relaxations of polar nanoregions with
strong relaxor-like characteristic. In addition, the microwave dielectric
measurements also revealed an unexpected and unusual anomaly in the relaxation
strength, which was related to a disruption of the antiferroelectric order
induced by a possible AFE-AFE phase transition.
