Ferroelectric behavior and spectroscopic properties of La-Modified lead titanate nanoparticles prepared by a sol-gel...

The sol-gel method was used to prepare perovskite type (Pb_1-1.5x La_x□_0.5x)TiO₃ (PLT) ceramics with x = 0.21, 0.22, 0.23, 0.24, 0.25 in order to investigate their structural, optical, and dielectric properties. The crystallite compounds were obtained by calcinating the mixture of PbCO₃, TiO₂, and La₂O₃ at 1000 °C for different time periods. After 4 h annealing, PLT23 sample, approximately a very little secondary phases have been observed in the XRD spectrum of the PLT sample with 23% La content (PLT23). The presence of La dopants might have affected the tetragonality of the Lead titanate crystal structure. The PLT samples tolerance factor decreases from 0.991 as in x = 0.21 to 0.986 for x = 0.25. Hence, these structures tend, generally, to be in the perovskite phase as t ~ 1. In the doped ceramics, characteristic phase transitions were shifted to lower temperatures. The dielectric permittivity value showed the tendency of a slight increase with lanthanum addition and achieved its maximum ε_m (3649) at x = 0.23, then it decreases for higher concentrations of La. The samples' estimated average crystallite size ranged from 40 nm to 50 nm, the maximum crystallite size about (49.6 nm) at x = 0.23 La. The calculated bandgaps were 3.1, 3.26, 3.28, 3.08, and 3.12 for the PLT with 0.21, 0.22, 0.23,0.24 and 0.25% La, respectively. The Curie constant C was obtained as the slope of the curve of the inverse values of ε_r vs. temperature. The highest C value (5.2 × 10⁵ K) was measured for the 23% La sample. The sample with 23% La content appears to be notably distinguished in its structural, optical, and dielectric characteristics compared with other samples.