Raman investigation of the composition and temperature-induced phase transition in (1-x)Pb(Fe_2/3W_1/3)O₃-xPbTiO₃ ceramics

The evolution with temperature of the Raman activity in the (1-x)Pb(Fe_2/3W_1/3)O₃-xPbTiO₃ solid solution with various compositions x∈(0, 1) was investigated. By increasing x, a general evolution of the system from disordered relaxor to ordered ferroelectric state with typical lines also observed in other Pb-based relaxors were found. The Raman activity present at few hundred degrees above the Curie region confirms the thermal stability of the nanopolar ordered regions in a nonordered average cubic state. For all the examined samples, the position, intensity, or damping of a few Raman lines exhibit anomalies in a range of temperatures which was considered related to the Curie region. The range of Curie regions corresponding to each composition is in very good agreement with the shift of Curie temperature as a function of x found by previous dielectric investigations. Two sharp peaks in the Pb(Fe_2/3W_1/3)O₃ spectra showed a maximum of their intensity at ≈500 K. This behavior is interpreted as due to critical changes in the dynamics of the nanopolar clusters at the freezing Burns temperatures in the present relaxor system.