Raman and infrared study of sol-gel grown lead magnesium niobate: Lead titante thin films

Abstract

Thin films of 0.7Pb(Mg_1/2Nb_2/3)O₃,−0.3PbTiO₃, (PMN-PT) were prepared by the sol-gel technique and deposited on platinum coated-silicon wafer. The thicknesses of the two films were ∼400 nm and ∼550 nm, respectively. Micro-Raman spectra of the PMN-PT films show strong broad bands centered at 50, 136, 276, 450, 510, 556, and 790 cm⁻¹, which are characteristics of PMN formation. Temperature-dependent Raman scattering from 290K to 70K did not show any significant change in the bandwidth of the peaks, meaning thereby that the relaxation times of these phonons are practically temperature independent. The bands are interpreted as due to a breakdown in the phonon momentum conservation within the Brillouin zone, which is associated with some degree of disorder in the material. As a result, the Raman spectrum is a weighted average of the density of phonon states. Micro-Raman measurements in many different places on the films clearly indicate that they are homogeneous. In addition, the differences found in the Raman spectra of the films, particularly the band at 790 cm⁻¹ is discussed. FT-JR measurements of the PMN-PT films present two broad bands around 260 and 550 cm⁻¹, which are characteristic of perovskite structure and are primarily due to motions of oxygen ions. Also, these bands are compared with those found in PMN single crystal, and with those found in other similar systems, such as PLZT and PSN. SEM and XRD techniques have been used for the structural characterization.