Temperature Dependent Raman Scattering and Dielectric Permittivity Measurements of Pb_(1-x)Sr_x TiO_3 Films

摘要

Pb_(1-x) Sr_x TiO_3 (x = 0 to 1.0) films of thickness ～ 4 μm have been prepared on sapphire and Pt substrates by metalorganic decomposition (MOD) method. X-ray diffraction results show that the films are polycrystalline with a perovskite tetragonal phase at room temperature for x < 0.5 and a cubic phase for x > 0.5. Room temperature Raman spectra show a systematic variation of lattice vibrational modes with x. The most notable changes in the Raman spectra with x are the decrease in the splitting of A_1(3TO) and E(3TO) modes and the disappearance of E(3TO) mode at x ～ 0.6. Although the x-ray diffraction peaks for films with x > 0.5 show a cubic phase at room temperature, the Raman spectra show the characteristic phonon modes of a tetragonal phase even at x = 0.7. The dielectric permittivity versus temperature measurements for films with x ≤ 0.7 show a broad dielectric anomaly corresponding to a diffuse ferroelectric to paraclectric phase transition. The phase transition temperature (T_c) values are consistently lower than the corresponding bulk ceramic alloys. Furthermore, T_c are also determined by monitoring the temperature dependence of the splitting between E(3TO) and A_1(3TO) phonon modes in the Raman spectra of Pb_(1-x)Sr_x TiO_3 films for x ≤ 0.6. There has been good agreement between the two methods.