**1. Introduction**

(Bi0.5Na0.5)TiO3 (BNT) was first reported by Smolenskii et al. in 1960 [1]. BNT ceramic is a kind of ABO3 type ferroelectrics which is replaced by Na<sup>+</sup> and Bi3 + complex ions at A-site. The A-site ions of BNT ceramics are located at the eight corner positions of octahedron, and the B-site ions are at the body center of octahedral structure [2]. Well sintered BNT ceramics have been obtained by hot pressing sintering method with d33 of 94–98 pC/N [3]. BNT ceramics exhibit a high Curie temperature (~320°C) and high polarization of 38 μC/cm<sup>2</sup> , which is considered to be one of the most promising environment-friendly ceramic system to replace lead-based ceramics [4].

Pure BNT ceramics exhibits some problems such as high conductivity, and large coercive field, consequently giving problems in the poling process [4], which seriously hinder its practical application. Studies show that the comprehensive properties of BNT system can be significantly improved by doping or by incorporation


### **Table 1.**

*Piezoelectric properties (d33) of BNT-based ceramics [9].*

with other components to form solid solutions. In recent years, investigation of BNT based ceramics mainly focuses on two aspects. On one hand, the phase transformation and structure change of BNT under external field (electric field, temperature and stress field). On the other hand, the properties enhancement of BNT-based were obtained by doping or by incorporation with other components to form solid solutions, such as Bi0.5Na0.5TiO3-BaTiO3(BNT-BT) [5], Bi0.5Na0.5TiO3- Bi0.5K0.5TiO3(BNT-BKT) [6] and other systems [7, 8] to promote its application in sensors and actuators.

At present, BNT system is mainly about its piezoelectric properties. The piezoelectric properties of well-known BNT-based system were reported in **Table 1** [9]. However, because of its strong ferroelectricity, BNT-based ceramics also exhibit great potential in the fields of energy storage, energy conversion and pyroelectric applications. In this chapter, new bismuth sodium titanate ceramics were synthesized and characterized, the ferroelectric properties, phase transition behaviors under external fields and related applications, such as application in energy storage, energy conversion and pyroelectric detection were proposed.
