Micro-Raman Characterization of the Phase Transition Behavior in Lanthanum Doped Lead Titanate Thin Films

Lanthanum-modified lead titanate, Pb 1 m x La x Ti 1 m x/4 O 3 (PLT), films with different compositions, such as x = 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30 were deposited on platinized silicon substrates using the sol-gel process. Raman scattering technique was utilized to study the dynamics of phase transitions and possible relaxor behavior in these compositions in a wide range of temperatures 100-873K. The outcome indicates change of the structure with the increase of La doping, as well as an increase in diffused phase transition behavior. The residual intensities of phonons above the tetragonal-to-cubic phase transition temperature suggest a diffuse nature of the ferroelectric phase transition, due to the short-range structural disorder in the paraelectric cubic phase. The Lyddane-Sachs-Teller (LST) relations were employed to analyze changes in the Raman mode positions in order to obtain the optical dielectric constants. The results are in good agreement with the previous dielectric studies.