**1. Introduction**

Over the years, piezoelectric materials have been heavily investigated for ultrasonic device applications. Of the many piezoelectric materials, Pb(Zr1−xTix) O3 (PZT)-based materials are more attractive for these applications, such as piezoelectric actuators, ultrasonic motors, and piezoelectric transformers [1–9]. As Pb(Mn1/3Nb2/3)O3 (PMnN), Pb(Zn1/3Nb2/3)O3 (PZN) have been found to be promising ferroelectric ceramics with good piezoelectric characteristics, high Curie temperature, they meet well with the requirements of ultrasonic transducer applications [6–8]. They are ferroelectric materials that have characteristics such as: high dielectric constant, the temperature at the phase transition point between the ferroelectric and paraelectric phase is broad (the diffuse phase transition), and a strong frequency dependency of the dielectric properties [6, 10–12]. The PZT-PZMnN ceramics, as one of PZT-Pb(B′, B″)O3 solid solutions, received more attention due to their high piezoelectric properties [6, 10–14]. So far, the sintering temperature of PZT-based ceramics is usually too high, approximately 1200°C [9]. To improve the sinterability and properties of lead piezoelectric ceramics, on the basis of the conventional solid phase sintering method, various advanced manufacturing techniques have been applied to the fabrication of lead ceramics such as the two-stage calcination method [15], high energy mill [16] and liquid phase sintering [9, 15, 17–20], hot isostatic pressing, hot pressing, microwave sintering, and spark plasma sintering [17] has been used effectively. Among them, the liquid phase sintering is a simple and effective method of improving the properties of PZT-based ceramics, which is currently attracting the interests of many scientists [15, 16]. By using various additives, such as NiO, B2O3, Bi2O3, Li2CO3, BiFeO3, ZnO, CuO, and Bi2O3, many researchers have successfully decreased the sintering temperature of PZT-based ceramics [5, 6, 13, 14, 18–23]. We also attempted decreasing sintering temperatures from 1150 to 930°C, which significantly improved the electrical properties of the ceramics. In these ceramics, Li2CO3 is considered as a liquid-phase sintering aid [5, 21, 24]. The addition of Li2CO3 improved the sinterability of the Bi0.5(Na0.8K0.2) 0.5TiO3 ceramic samples and caused an increase in the density and grain size at a sintering temperature of 1100°C [19]. With increasing Li2CO3 content, the phase structure of the ceramics changed from rhombohedral to tetragonal, indicating that it is close to the morphotropic phase boundary (MPB) of this system.

In this chapter, in order to develop the composition ceramics for highintensity ultrasound applications, *x*Pb(ZryTi(1−y))O3-(0.925-*x*)Pb(Zn1/3Nb2/3) O3-0.075Pb(Mn1/3Nb2/3)O3 (PZT-PZN-PMnN) ceramics were fabricated by the B-site oxide mixing technique. The aim of the chapter was, first, to carry out a phase formation, piezoelectric, ferroelectric, and dielectric characteristics in a solid solution of PZT-PZN-PMnN. The compositions synthesized in this study were *x* = 0.65, 0.70, 0.75, 0.80, 0.85, and 0.90 in the ternary system, *x*Pb(Zr0.47Ti0.53) O3-(0.925 − *x*)Pb(Zn1/3Nb2/3)O3-0.075Pb(Mn1/3Nb2/3)O3. Then detailed systematic structural analysis and the study of physical properties were carried out for *x* = 0.8 compositions by varying the value of *y* in the Zr/Ti ratio. This will help to better determine how variations in the phase content affect local atomic arrangements and hence the electrical properties; and, second, to study the effect of ZnO nanoparticles on the sintering behavior and electrical properties of 0.8Pb(Zr0.48Ti0.52) O3-0.125Pb(Zn1/3Nb2/3)O3-0.075Pb(Mn1/3Nb2/3)O3 piezoelectric materials; the application, fabrication of ultrasonic transducers are reported and discussed.
