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The a.c. complex impedance spectroscopy technique was used to obtain the electrical parameters of (Na 0.5 Bi 0.5 ) 0.94 Ba 0.06 TiO 3 + 0.3 wt% Sm 2 O 3 + 0.25 wt% LiF lead-free ceramics in a wide frequency range at different temperatures. These samples were prepared by a high-temperature solid-state reaction technique and their single phase formation was confirmed by the X-ray diffraction technique. Dielectric studies exhibit a diffuse phase transition characterized by a temperature and frequency dispersion of permittivity, and this relaxation has been modelled using the modified Curie-Weiss law. The variation of imaginary part (Z ) of impedance with frequency at various temperatures shows that the Z values reach a maxima peak (Z max ) above 400 • C. The appearance of single semicircle in the Nyquist plots (Z vs. Z ) pattern at high temperatures suggests that the electrical process occurring in the material has a relaxation process possibly due to the contribution for bulk material only. The bulk resistance of the material decreases with rise in temperatures similar to that of a semiconductor, and the Nyquist plot showed the negative temperature coefficient of resistance (NTCR) character of these materials. The frequencies, thermal effect on a.c. conductivity and activation energy have been assessed.

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