Dielectric and piezoelectric properties of BiScO₃-PbTiO ₃ crystals with morphotropic phase boundary composition

The room temperature dielectric permittivity of [100] oriented 0.37BiScO₃-0.63PbTiO₃ (BSPT63) crystals with a morphotropic phase boundary (MPB) composition was found to be 1400, lower than that of BSPT57 crystals with rhombohedral phase (∼3000), but much higher than that of the tetragonal crystal BSPT66 (∼200). The Curie temperature of BSPT63 single crystals along [100] was found to be about 443°C, while the values were around 440°C and 445°C for [110] and [111] oriented crystals, respectively. Evidence of a ferroelectric-ferroelectric phase transformation temperature was associated with a dielectric anomaly occurring around 310-350°C for different orientations, indicating a strong curvature of the MPB. The coercive fields (E_c) were found to be 20kV/cm for [100] oriented crystals, 24kV/cm and 27kV/cm for [110] and [111] directions, respectively. The piezoelectric response for [100] oriented samples (d ₃₃ = 900pC/N) is weaker than that in rhombohedral phase (d ₃₃ = 1200pC/N) but much higher than that in tetragonal phase (d ₃₃ =200 pC/N). The strain piezoelectric d₃₃ improved with the temperature increasing owing to dielectric permittivity increment, while the voltage piezoelectric g₃₃ is independent of temperature (g ₃₃ ∼0.074 m²/C). Evidence of a monoclinic phase for BSPT63 crystals is inferred using the X-ray powder diffraction (XRD), and the lattice parameters were calculated to be a = 4.0751 Å, b = 3.9765 Å, c = 3.9893 Å and β= 90.166°.