Phase Diagram in La-modified Pb(Sc_1/2Nb_1/2)O₃–PbTiO₃Binary Ceramics System

The phase boundaries in La-modified Pb(Sc1/2Nb1/2)O3–PbTiO3 system (La-PSN/PT), expressed as Pb(1-x)Lax[(Sc1/2Nb1/2)yTi(1-y)](1-x/4)O3, were determined. The phase diagram was found to consist of three phases: paraelectric cubic, ferroelectric tetragonal and ferroelectric rhombohedral at room temperature. The Curie temperature of the solid-solution ceramics decreases with increasing La content. The plot of the Curie temperatures of the samples with different La-PSN/PT compositions obtained at about 25°C, presents a curve from the composition of La-PSN/PT 2.5/100/0 to 25.5/0/100. Above room temperature, the morphotropic phase boundary (MPB) plots a straight line from composition 0/57.5/42.5 to 12.2/60.9/39.1. The electrical properties of the binary ceramics materials near the MPB were investigated.