Relationship between low frequency dielectric dispersion and ferroelectric phase transition in pulsed-laser-deposited Bi4-xLaxTi3O12 thin film

The frequency and temperature dependence of the complex dielectric constant of Bi4-xLaxTi3O12 (BLT, x = 0.9) ferroelectric thin film was studied in the frequency range of 10(-1) similar to 10(6) Hz and the temperature range of 298 similar to 673 K. A low frequency dielectric dispersion (LFDD) was found. A model was proposed to account for this observed phenomena. The complex dielectric constant data obtained in the measured frequency and temperature ranges have been found to fit very well to the dielectric dispersion relation: epsilon* = epsilon(infinity) + isigma/epsilon(o)omega + [B(iomega)(n-1)]/epsilon(o). The knee in the log of the electrical conductivity versus the reciprocal temperature curve occurs at T-c. The activation energies associated with charge conduction are E-a,E-II = 0.73 eV below T-c and E-a,E-I = 0.95 eV above T-c. The occurrence of an anomaly in both the n and epsilon(infinity) parameters near T-c indicates a coupling between charge carries and phonons.