Phase evolution and relaxor behavior of BiScO₃–PbTiO₃–0.05Pb(Yb_1/2Nb_1/2)O₃ ternary ceramics

High-temperature piezoelectric ceramics (0.95 − x)BiScO₃–xPbTiO₃–0.05Pb(Yb_1/2Nb_1/2)O₃ (BS–xPT–PYN, x = 0.56–0.64) were prepared by a conventional solid-state reaction method. X-ray diffraction and Raman spectra demonstrated that the ceramics convert from monoclinic phase (x ≤ 0.58) to tetragonal phase (0.62 ≤ x ≤ 0.64). A phase coexistence of monoclinic and tetragonal in the vicinity of the MPB (x = 0.60) enhances the ferroelectric polarizability by a dynamical conversion between two energy-degenerate states with d₃₃ = 392 pC/N, k_p = 53.3% and P_r = 38.8 μC/cm² and the operation temperature up to ~ 400 °C. Relaxor behaviors, which following the V–F law, are presented in this system and their dipole activation energy decrease for higher component x. The phase fraction versus temperature of the MPB (x = 0.60) was investigated by an in situ XRD, which gives an insight into the origin of the high-temperature piezoelectricity.