**6. Ferroelectric domain structures around the morphotropic phase boundary of the 0.8Pb(Zr0.48Ti0.52)O3-0.125Pb(Zn1/3Nb2/3)O3- 0.075Pb(Mn1/3Nb2/3)O3 ceramics**

In this section, in order to develop the composition ceramics for highintensity ultrasound applications, 0.8Pb(Zr0.48Ti0.52)O3–0.125Pb(Zn1/3Nb2/3) O3–0.075Pb(Mn1/3Nb2/3)O3 + *z* wt% ZnO nanoparticles ceramics were fabricated by the B-site oxide mixing technique with the variations of *z* and then the phase formation, piezoelectric and dielectric characteristics were investigated with the variations of *z.* The general formula of the studied materials is 0.8Pb(Zr0.48Ti0.52) O3–0.125Pb(Zn1/3Nb2/3)O3–0.075Pb(Mn1/3Nb2/3)O3 + *z* wt% ZnO, where *z* = 0.0, 0.20, 0.25, 0.30, 0.35, 0.40, and 0.45. The obtained ZnO nanoparticles are spherical in shape, with their average diameter about 27 nm [9, 18]. On the other hand, reagentgrade oxide powders of PbO, ZnO, MnO2, Nb2O5, ZrO2, and TiO2 (purity ≥99%) were used as starting raw materials for the fabrication of the PZT-PZN-PMnN ceramics.

**Figure 19** shows X-ray diffraction patterns of the PZT-PZN-PMnN ceramics at various contents of ZnO nanoparticles. All the compositions have demonstrated pure perovskite phases and no trace of the second phase. Further XRD analysis is performed in the 2θ ranges from 43 to 46°, as shown in the inset of **Figure 19**. It can be seen that a phase transformation from the rhombohedral structure to the tetragonal structure occurs with increasing ZnO content. The samples with *z* = 0.0 and 0.2

*The Investigation on the Fabrication and Characterization of the Multicomponent Ceramics… DOI: http://dx.doi.org/10.5772/intechopen.93534*

have the rhombohedral structure characterized by a peak (200)R at 2θ ≈ 44.5°. With *z* = 0.40 and 0.45, the ceramics exist as a tetragonal phase which is indicated by the splitting of (002)T and (200)T peaks in the 2θ range from 44 to 45° [23, 53, 54]. In the *z* range from 0.25 to 0.35, the ceramics coexist as rhombohedral and tetragonal phase, which is revealed by the coexistence of (002)T, (200)T, and (200)R peaks. Therefore, it could be said that the composition *z* from 0.25 to 0.35 is close to the morphotropic phase boundary (MPB) of this system. The phenomenon can be explained by the penetration of Zn2+ ions into the grains to substitute for B-site ions due to the similar radii of Zn2+ (0.074 nm), Ti4+ (0.0605 nm), Zr4+ (0.072 nm), and Nb5+ (0.064 nm) at the octahedral sites of the perovskite lattice, forming additional anionic vacancies. This causes a distortion in the lattice; therefore, the substitution of Zn2+ ions at Ti4+ or Zr4+ sites caused the c-axis to be lengthened and changed in lattice parameters and degree of tetragonality (c/a). These results are consistent with the literature [5, 19, 21, 48, 55].

Effects of the contents of ZnO nanoparticles on the microstructure development of the ceramics are shown in **Figure 20**. As can be described in the microstructure of

**Figure 19.**

*X-ray diffraction patterns of PZT-PZN-PMnN ceramics at various contents of ZnO nanoparticles [9].*

### **Figure 20.**

*Microstructures of PZT-PZN-PMnN ceramics at different contents of ZnO nanoparticles: (a) 0.20 wt%, (b) 0.25 wt%, (c) 0.3 wt%, (d) 0.35 wt%, (e) 0.40 wt%, and (f) 0.45 wt%.*

**Figure 21.** *The domain structures micrographs of the PZT-PZN-PMnN ceramics; (a) 0.4 wt% ZnO; (b) 0.35 wt% ZnO [9].*

ceramics, the grain size of PZT-PZN-PMnN samples is increased with the increasing content of ZnO nanoparticles. This may explain that the low melting point of ZnO nanoparticles is beneficial to generate eutectic liquid phase at low temperature, and it can act as lubrication during the sintering process, wetting solid particles and providing capillary pressure between them, thus resulting in faster grain growth of PZT-PZN-PMnN ceramics [56, 57]. However, when the ZnO concentration is large, it exceeds the solubility limit of ZnO into the ceramics, and they will be located at grain boundaries preclude the grain growth process, as shown in **Figure 20(d)**–**(f)**.

**Figure 21** shows evolution examples of the ferroelectric domain with the rhombohedral to tetragonal phase transformation and the grain size of the PZT-PZN-PMnN samples of about 2 μm. The SEM images of the domain structure suggest the presence of 90 and 180° domains in the tetragonal phase (**Figure 21(a)**), whereas the 71, 109, and 90° domains are located in the red-bordered region and primarily viewed in **Figure 21(b)**), and the widths of these domains were about 100 nm. Inspection of SEM images acquired at lower magnifications showed that the abundance and scale of these microtwin structures varied with location both within and between ceramic grains, with abrupt changes in the domain structure occurring at the grain boundaries [58]. One of the important contributions from our experimental works is the confirmation of the SEM images by corrosion method as a valid method for domain size assessment in bulk ceramics.
