High Effective Lead Perovskite Ceramics and Single Crystals for Ultrasonic Imaging

Some complex lead perovskites, namely Pb(B′B″)O₃ (B′ = Mg, Zn, Ni, Fe, Sc, In, and Yb; B″ = Nb, Ta, and W), are relaxors with the rhombohedral or monoclinic structure and tetragonal structure with lead titanate PbTiO₃ (PT); these perovskites exhibit a morphotropic phase boundary (MPB) and large electromechanical coupling factor and dielectric constants near the MPB [1–8]. Table 9.1 shows the Curie temperature (T _c,), maximum dielectric constant (K), crystal structure, ferroelectric (F) or antiferroelectric (AF) phase, PbTiO₃ mol(%) at the MPB, and T _c at the MPB for various relaxor materials, along with their abbreviations. Figure 9.1 shows the MPB (I) in PZT and the MPB (II) in Pb(B′B″)O₃-PbTiO₃ and the MPB (III) in Pb(B′B″)O₃-PZT. The locations of the MPB (II) and (III) vary when different B′ or B″ ions are selected as shown in Fig. 9.1. As regards practical piezoelectric applications, little attention was paid to MPB (II) and (III) compositions until 1980, due to the poor piezoelectric properties of the ceramics, notably their low electromechanical coupling factors compared to those of PZT ceramics, and the high cost of the raw materials. Initially, lead magnesium niobate, Pb(Mg_1/3Nb_2/3)O₃ (PMN), lead nickel niobate, Pb(Ni_1/3Nb_2/3)O₃ (PNN), and lead zinc niobate, Pb(Zn_1/3Nb_2/3)O₃ (PZN), were considered to be the three best relaxors.