Dielectric and vibrational properties of La³⁺ substituted relaxor (Na_1/2Bi_1/2)TiO₃ ceramics

Different concentrations of A-site substitute La³⁺ were selected to modify (Na_1/2Bi_1/2)TiO₃ ceramics. Dielectric permittivity and dissipation factor (tan δ) of (Na _1/2Bi_1/2-xLa_x)TiO₃ (x = 0.5 %, 1 %, 5 % and 10 %) were measured at room temperature. Raman scattering was performed on all components at room temperature. From the dielectric measurement, we can conclude that both permittivity and tan δ markedly depend on frequency. At low frequency, permittivity and tan δ varied, and increased with La³⁺ concentration. However, in comparison with those at low frequency, permittivity and tan δ changed little at high frequency. The Raman spectra show that all bands are relatively broad, which is mainly due to the disorder on the A-site ions of perovskite structure. The bands around 130 cm^-1 and 270 cm^-1 were selected to analyzed, since they are well separated from others. With an increase of La³⁺ concentration, the band around 130 cm^-1 showed nearly no shift, while the band around 270 cm^-1 shifted to lower frequency.