The dielectric properties have been investigated in lead–free $({\mathrm{Bi}}_{0.5}{\mathrm{Na}}_{0.5}{)}_{0.92}{\mathrm{Ba}}_{0.08-3x/2}{\mathrm{La}}_x{\mathrm{TiO}}_3$ ($x$ = 0, 1, 2 and 3 at.%) ceramics. The dielectric response exhibited three anomalies in the temperature dependence of the dielectric permittivity, which have been associated to different phase–transitions in the studied temperature range. In addition, a strong dielectric dispersion, with relaxor-like characteristics, has been observed at low temperatures, for temperatures around the first dielectric anomaly, as the frequency increases, revealing a significant contribution of the conduction mechanisms in the dielectric response of the studied ceramics. By using the Cole-Cole’s formalism, the observed behavior revealed to be associated to relaxation processes related to the mobility of intrinsic defects promoted by polaron mechanisms. The obtained value for the conductivity-based activation energy, obtained by using the Arrhenius’ law, revealed to decreases with the increase of the lanthanum (${\mathrm{La}}^{3+}$) concentration, showing the major contribution of the AC conductance for the compositions with higher lanthanum content.

$\mathbf{ACKNOWLEDGMENTS}\mathbf{:}$ The authors would like to acknowledge the Third World Academy of Sciences (RG/PHYS/LA Nos. 99-050, 02-225 and 05-043), and the Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste-Italy, for financial support of Latin-American Network of Ferroelectric Materials (NET-43, currently NT-02). Thanks to CNPq and FAPEMIG Brazilian agencies for financial support. MSc. Mendez-González also acknowledges the receipt of the grant (No. AF-13/17-01) from the ICTP, Trieste, Italy.