Raman Scattering at Phase Transformations in the Relaxor Ferroelectric PbCo1/3Nb2/3O3

Abstract

In this paper, we present the results of studies of the phonon and relaxation subsystems in the relaxor ferroelectric crystal PbCo_1/3Nb_2/3O₃ (PCN) using Raman scattering in the temperature range from 650 to 80 K, including the regions of “diffuse phase transition” with a maximum permittivity \({{T}_{m}} \approx 250{\kern 1pt} \) K at a frequency of 1 kHz and charge phase separation in the vicinity of 170 K. It has been shown that the polarized spectra of PCN are similar to those observed in relaxor ferroelectrics with a perovskite structure. The analysis of the temperature behavior of the main phonon modes and anisotropic quasielastic light scattering revealed anomalies in the region corresponding to the onset (\({{T}_{2}} \sim 230{\kern 1pt} \) K) and final formation (\({{T}_{3}} \sim 170{\kern 1pt} \) K) of charge phase separation, determined by the presence of Co²⁺ and Co³⁺ ions in the PCN crystal. Anomalies in the evolution of the Raman spectra near the temperature of the relative permittivity maximum \({{T}_{m}}\), which are characteristic of relaxor ferroelectrics, were not observed in PCN. The dynamics of polar nanoregions, which determine the behavior of quasielastic light scattering, differ from those observed in the model relaxor ferroelectric PbMg_1/3Nb_2/3O₃ (PMN).