Dielectric and Piezoelectric Properties of BiScO3-PbTiO3 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 20 kV/cm for [100] oriented crystals, 24 kV/cm and 27 kV/cm for [110] and [111] directions, respectively. The piezoelectric response for [100] oriented samples (d 33 = 900 pC/N) is weaker than that in rhombohedral phase (d 33 = 1200 pC/N) but much higher than that in tetragonal phase (d 33 = 200 pC/N). The strain piezoelectric d 33 improved with the temperature increasing owing to dielectric permittivity increment, while the voltage piezoelectric g 33 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°.