Synthesis, structural evolution, and dielectric properties of a new perovskite solid solution (Pb_0.5Sr_0.5)(Zr_0.5Ti_0.5)O₃–PbTiO₃

To explore lead-reduced dielectric materials in the SrTiO₃–PbTiO₃–PbZrO₃ ternary system, a novel solid solution between relaxor ferroelectric (Pb_0.5Sr_0.5)(Zr_0.5Ti_0.5)O₃ and ferroelectric PbTiO₃, namely (1 − x)(Pb_0.5Sr_0.5) (Zr_0.5Ti_0.5)O₃–xPbTiO₃ (lead–strontium–zirconate–titanate [PSZT]–PT), has been synthesized in the perovskite structure by high-temperature solid-state reaction method in the form of ceramics. The crystal structure and phase symmetry of the materials synthesized were analyzed and resolved based on X-ray powder diffraction (XRD) data through both the Pawley and Rietveld refinements. The results of the structural refinements indicate that at low PT-concentration end of the solid solution system, for example, x = 0.05, the PSZT–PT solid solution exhibits a cubic structural symmetry (with the space group Pm-3m). As the PT concentration (x) increases, the structure of (1 − x)PSZT–xPT gradually transforms from the cubic to a tetragonal (P4mm) phase. In the composition range of x = 0.10–0.25, a mixture of the cubic and tetragonal phases was identified. As the concentration of PT increases, the proportion of the tetragonal phase increases at the expense of the cubic phase. For a composition of x > 0.25, a pure tetragonal phase is observed. The dielectric properties of the materials were studied by measuring the permittivity as a function of temperature at various frequencies. For the composition of x = 0.05, the temperature dependence of dielectric constant shows typical relaxor behavior. For x = 0.35, the dielectric peaks indicate a normal ferroelectric phase transition. Overall, a structural transformation from a central-symmetric, nonpolar cubic phase to a non-centrosymmetric, polar tetragonal phase is induced by the substitution of PT for PSZT in the pseudo-binary solid solution of (1 − x)PSZT–xPT, which also reveals an interesting relaxor to ferroelectric crossover phenomenon.