The chemical composition of the PZT-PZN-PMnN ceramics.
This chapter presents the investigation of fabrication and the physical properties of the Pb(Zr1−xTix)O3-Pb(Zn1/3Nb2/3)O3-Pb(Mn1/3Nb2/3)O3 multicomponent ceramics. The multicomponent yPb(Zr1−xTix)O3-(0.925 − y)Pb(Zn1/3Nb2/3)O3-0.075Pb(Mn1/3Nb2/3)O3 (PZT-PZN-PMnN) ceramics were synthesized by conventional solid-state reaction method (MO) combined with the B-site oxide mixing technique (BO). Research results show that the electrical properties of PZT-PZN-PMnN ceramics are optimal at a PZT content of 0.8 mol and Zr/Ti ratio of 48/52. At these contents, the ceramics have the following optimal properties: electromechanical coupling factor, kp = 0.62 and kt = 0.51; piezoelectric constant (d31) of 130 pC/N; mechanical quality factor (Qm) of 1112; dielectric loss (tan δ) of 0.005; high remanent polarization (Pr) of 30.4 μC.cm−2; and low coercive field (EC) of 6.2 kV.cm−1. Investigation of the domain structure of the two ferroelectric phases (tetragonal and rhombohedral) in the ZnO-doped PZT-PZN-PMnN with compositions at near the morphotropic phase boundary is described as follows: the 90 and 180° domains exist in the tetragonal phase, while the 71, 109, and 90° domains are located in the rhombohedral phase, and the widths of these domains were about 100 nm. Besides, the ceramics exhibited excellent temperature stability, which makes them a promising material for high-intensity ultrasound applications.
- the multicomponent ceramics
- ZnO nanoparticles
- the ultrasonic transducers
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, 2, 3, 4, 5, 6, 7, 8, 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, 7, 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, 11, 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, 11, 12, 13, 14]. So far, the sintering temperature of PZT-based ceramics is usually too high, approximately 1200°C . 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 , high energy mill  and liquid phase sintering [9, 15, 17, 18, 19, 20], hot isostatic pressing, hot pressing, microwave sintering, and spark plasma sintering  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, 19, 20, 21, 22, 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 . 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 high-intensity ultrasound applications,
2. Synthesis of PZT-PZN-PMnN ceramics by the B-site oxide mixing technique
Lead-based mixed B-site cation perovskites of (B′, B″)O3-type exhibit diffuse phase transition (DPT) behaviors of broad dielectric constant spectra in contrast to the sharp phase transitions of Pb(Zr,Ti)O3 and PbTiO3 . The complex perovskite compounds are difficult to synthesize by conventional solid-state reaction method owing to the formation of pyrochlore phases and reduction of desirable properties, such as the electromechanical coupling factor and dielectric constant, which originate from the perovskite structure . The B-site oxide mixing technique (BO) [26, 27] (formation of a B-site precursor of (B′, B″)O2-type, followed by a reaction with PbO) has been applied to several complex perovskite compositions and the results are quite successful [22, 28, 29]. In the conventional method (MO), oxide powders of PbO, ZrO2, TiO2, ZnO, MnO2, and Nb2O5 were weighed and milled for 8 h. To identify the temperature for calcining PZT-PZN-PMnN, we investigated the data of thermal gravimetric (TG) and thermal analysis (DTA) of PZT-PZN-PMnN powder (Figure 1). As per the above results, the TG curve exhibits a linear decrease in the total mass of the studied powder. However, the DTA curve shows an endothermic peak from 739 to 840°C, corresponding to the ion evaporation. To ensure the phase creation in the sample, the mixture powder was calcined at temperatures a little higher than 850°C after being milled for 8 h and pressed into pellets . Afterward, the calcined PZT-PZN-PMnN pellets were continued to be milled for 16 h and pressed into disk 12 mm in diameter and 1.5 mm in thick under 100 Tan/cm2.
In the B-site oxide mixing technique, in order to identify the temperature for calcining of (Zn,Mn)Nb2(Zr,Ti)O6 (BO), we investigated the data for thermal gravimetric (TG) and thermal analysis (DTA) of (Zn,Mn)Nb2(Zr,Ti)O6 powders, as shown in Figure 2. As per results, the TG curve of the mixture powder shows that the total mass of the studied powder decreases linearly. However, the DTA curve shows the endothermic peak at 978°C, corresponding to the temperature of powder evaporation. In order to ensure that the temperature is at least above 978°C for each powder grain, the mixture powder was calcined at little higher temperature of 1100°C [6, 11, 21, 22] after the powders of BO and PbO were weighed and milled for 8 h.
The powders were calcined at a temperature of 850°C for 2 h, producing the PZT-PZN-PMnN compound. The samples were sintered at 950°C for 2 h. Figure 3 shows the X-ray diffraction (XRD) patterns of the PZT-PZN-PMnN ceramics prepared by different methods. From X-ray diagrams, we can see that the BO sample has only pure perovskite phase with rhombohedral structure, and this was determined by the (
3. Characterization of ceramics
The crystalline structure of the sintered ceramics was analyzed by X-ray diffraction (XRD) analysis at room temperature. The surface morphology was examined using field emission scanning electron microscopy (SEM), X-ray energy dispersive spectra (EDS) was measured using a Hitachi S-3400N scanning electron microscope with an EDS system Thermo Noran, and the densities of the ceramic samples were measured by the Archimedes method from the ceramic samples weighed in air, in water and the density of water. The grain size is determined from SEM micrographs by a linear intercept method. The dielectric properties of ceramics (relative dielectric constant and dielectric loss) were measured with a HIOKI 3532 impedance analyzer. The electromechanical coupling factors
4. The effects of Pb(Zr0.47Ti0.53)O3 on the structure, microstructure, and the dielectric properties of
xPb(Zr0.47Ti0.53)O3-(0.925 − x)Pb(Zn1/3Nb2/3)O3-0.075Pb(Mn1/3Nb2/3)O3 ceramics
Lead-zinc niobate Pb(Zn1/3Nb2/3)O3 (PZN) materials were first synthesized in the 1960s [35, 36]. It is one of the well-known relaxor perovskite ferroelectrics exhibiting a diffused phase transition with a phase transition temperature around 140°C (
Figure 5 shows XRD patterns of the PZT-PZN-PMnN ceramics at various contents of PZT. As observed, all ceramics have pure perovskite phase with dominantly tetragonal structure. The lattice parameters (
|Elements||The mass percentage of elements from the precursors||Mass percentage of elements from the synthesized ceramic|
Figure 7 shows microstructures of the PZT-PZN-PMnN ceramics at various contents of PZT. The average grain size of these samples is increased with the increase of PZT content in Table 2. On the other hand, the average grain size is reduced when x increases above 0.8. These results are obviously consistent with the change in the density of PZT content of PZT-PZN-PMnN ceramics, as shown in Table 2.
|Average grain size (μm)||0.56 ± 0.02||0.66 ± 0.02||0.90 ± 0.02||1.04 ± 0.01||0.85 ± 0.02||0.83 ± 0.03|
|The average density of ceramics (g/cm3)||7.77 ± 0.02||7.78 ± 0.01||7.80 ± 0.01||7.81 ± 0.01||7.72 ± 0.01||7.69 ± 0.02|
Table 2 shows the density of the PZT-PZN-PMnN ceramics as a function of the PZT content. With the increase of PZT content up to 0.8, the mass density of PZT-PZN-PMnN ceramics increases. It achieves a maximum value (
where n = number of atoms associated with each unit cell in ABO3, A = atomic weight, VC = volume of the unit cell in ABO3, and NA = Avogadro’s number.
This is explained by the content of PZT was added to the ceramic system is less than 0.8 mol, a large number of pores were present, indicating insufficient densification of the sample (Figure 7: some SEM for M70, M90 are missing and M75 is not good). As the PZT content increases, the ceramics became denser, and the sample was almost fully dense at a PZT content of 0.8 mol.
The PZT content dependence of the dielectric constant (
In order to characterize the dielectric loss of all samples, the measurement of dielectric constant dependent on temperature is carried out at 1 kHz, as shown in Figure 8. With increasing PZT content, the dielectric constant peak increases and becomes sharpened. Hence, the material properties change from relaxor ferroelectricity to normal ferroelectricity. The permittivity and the maximum temperature (
The slopes of the fitting curves (Figure 9) are used to determine the
5. The effects of Zr/Ti ratio on the structure, microstructure, and the electrical properties of 0.8Pb(Zr
yTi1− y)O3–0.125Pb(Zn1/3Nb2/3)O3–0.075Pb(Mn1/3Nb2/3)O3 ceramics
The influence of Zr/Ti ratio on the structure of PZT-PZN-PMnN ceramics has been analyzed through the X-ray diffraction patterns (Figure 11). The patterns reveal a pure perovskite phase for all ceramic samples.
As can be seen, the tetragonality of PZT-PZN-PMnN ceramics decreased with increasing Zr/Ti ratio content through the c/a ratio decreases. According to Dixit et al.  and Kahoul et al. , the morphology of Pb(Zr,Ti)O3 ceramics is strongly dependent on the Zr and Ti content. The content of the rhombohedral phase gradually increases within decreasing the Zr content simultaneously, and the tetragonal phase gradually decreases. The morphological evolution with Zr contents in this work may be attributed to the increase of a rhombohedral phase in these ceramics [46, 47]. This may be because the large Zr+4 (0.86 Å) ions diffuse into the PZT-PZN-PMnN lattice to replace Ti4+ (0.61 Å), resulting in the increase in the lattice constant and a shift in the XRD peak position toward lower 2
Effects of the contents of Zr/Ti ratio on the microstructure development of the ceramics are shown in Figure 12. In general, surface ceramics with large grains and uniform microstructure were obtained in all samples, and the average grain size of samples is increased with the increasing content of Zr/Ti ratio. In conformity with the previous densification results, highly dense samples exhibited high degrees of grain close packing. However, some pores and abnormal grain boundaries were observed in Figure 12 (MZ50 and MZ51) and the average grain size is reduced.
Figure 13 shows the temperature dependence of
In order to determine the piezoelectric properties of ceramics, resonant vibration spectra of the PZT-PZN-PMnN samples were measured at room temperature (Figure 15), and from these resonant spectra, the piezoelectric parameters of the samples, such as electromechanical coefficients
The effect of temperature on the ferroelectric properties of ceramics was studied by the hysteresis loops of the 0.8Pb(Zr0.48Ti0.52)O3–0.125Pb(Zn1/3Nb2/3)O3–0.075Pb(Mn1/3Nb2/3)O3 sample in the temperature range of 30–280°C (Figure 18(a)). The hysteresis loops of the ceramics exhibited excellent temperature stability due to the broad diffusive phase transition between the nonergodic and ergodic relaxor states that coexisted over a wide temperature range . When the temperature increased from room temperature to 120°C, the remanent polarization and the coercive field increased (Figure 18(b)). The reason is when the temperature increases, the oxygen vacancies in the perovskite structure will move and significantly increase the conductivity of the material, which should increase the dielectric loss. However, when the temperature rises above 120°C, the remanent polarization
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 high-intensity ultrasound applications, 0.8Pb(Zr0.48Ti0.52)O3–0.125Pb(Zn1/3Nb2/3)O3–0.075Pb(Mn1/3Nb2/3)O3 +
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
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 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 . 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.
This chapter presents the investigation on the fabrication and characterization of sample groups of PZT-based ceramics and the relaxor PZN-PMnN ferroelectric materials with perovskite structure. The B-site oxide mixing technique reported in this study is simple, produces large quantities, and is easy to reproduce. Experimental results showed that the electrical properties of
This research is funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) under Grant Number 103.02-2017.308.