**3.3. Fabrication of composite**

high symmetry. However, the order–disordered NaNbO3 presents a symmetry rupture along the O–Nb–O bonds that result in complex clusters with different coordination numbers ([NbO6]–[NbO5]) or distortions in the [NbO6]–[NbO6] octahedral clusters. The wide-band visible emission observed is a characteristic property of practically all self-activated ABO3

Some materials present a change in the PL emission according to the morphology [31]. However, as far as our investigation is concerned, the PL results are seen not to be related to the morphology of the NaNbO3 but rather to the organization of the crystalline structure. This observation is backed by the results observed in [22] where the orthorhombic NaNbO3 presents fiber-like and cubic-like particles, where both have PL emission in the same region. The PL emission region observed here is not the same for Na2Nb2O6.nH2O which presents fiber-like

The microwave hydrothermal process is capable of producing NaNbO3 with a more disor‐ ganized structure when compared to NaNbO3 obtained by thermal treatment of Na2Nb2O6.nH2O. This can be associated to the heating of Na2Nb2O6.nH2O so as to yield NaNbO3 with fiber-like morphology which tends to promote a better self-assembly of the crystalline structure than in cubic-like particles. This assembly decreases the structural defects as well as the intermediary levels within the band gap, resulting in a lower PL emission [22].

PVDF is a piezoelectric polymer (d33= –33 pC/N) that is able to produce variation in the surface charge when subjected to mechanical stress without requiring additional energy sources or electrodes for the generation of electrical signal. This polymer consists of a carbon-based chain with alternating hydrogen and fluorine units (–CH2–CF2–)n, and its molecular weight is around 105 g.mol–1. PVDF presents polymorphism and can be found in four structural phases (α, β, γ and δ) where the piezoelectric phase is said to be the β phase once it is a polar phase

PAni (polyaniline) is a conducting polymer in which the electrical conductivity can be modified by the protonation process controlling the reaction pH [15], and its use to cover

To obtain PAni, the monomer aniline (C6H5NH2) (Sigma-Aldrich) was used after vacuum distillation to remove photoxidized molecules. The oxidant ammonium persulfate was

To obtain NaNbO3 fiber particles coated with PAni, the fibers were incorporated into a solution of aniline, cloridric acid water solution, 1 mol.L–1, and ammonium persulfate under stirring at

**3.2. Obtaining NaNbO3 1D nanostructures modified by polyaniline (PAni)**

ceramic particles has the ability to improve the conductivity of particles.

employed for the polymerization process of aniline (MERCK).

perovskites [22,30].

68 Ferroelectric Materials – Synthesis and Characterization

particles to boot [22].

**3. Composite processing**

**3.1. Polymer matrix: PVDF**

[8,32].

α-PVDF in powder form was mixed in a mortar with pure NaNbO3 particles with both morphologies (fiber and cubic particles). In addition, the NaNbO3 fiber-like particles coated with PAni were mixed in a mortar with PVDF until a homogeneous mixture was formed. The mixtures were then placed between sheets of Kapton and hot pressed at 190°C for 5 minutes with a pressure of 5 MPa. The thickness of the films is in the range of 190 to 500 μm depending on the ratio of ceramic/polymer content. The composite films from pure NaNbO3 particles were obtained with volumetric fractions of ceramic (30%, 40%, 50% and 60%), while those from NaNbO3 fibers modified with PAni were obtained with 30% and 40% of volume fraction of ceramic. The composites obtained from fiber-like particles without PAni will be denoted by FbNN while the particles coated with PAni will be denoted by PbNN-PAni*rep*, and composites from cubic-like particles will be represented by CbNN.

The volume fraction of ceramic was calculated using the equation 5 [8,33].

$$\mathfrak{m}\_c = \frac{\mathfrak{m}\_p \rho\_c}{\rho\_p} \frac{\Phi\_c}{1 - \Phi\_c} \tag{5}$$

In the equation *m* is the mass and **ρ** is the density. The subscript *c* and *p* are related to ceramic and polymer, respectively. Φ*c* is the volume fraction of ceramic.

Figure 7, 8 and 9 show the FE–SEM images of the composite sample. The distribution of the ceramic particles in the polymer matrix likewise the difference between the samples surface according to the increase in the ceramic particles can be observed. The inhomogeneity of the sample with 60% of ceramic particles led to the lowest flexibility of the composite owing to the high concentration of particles and the change in connectivity.

**Figure 7.** FE–SEM of surface of FbNN composites with the respective volume fraction of NaNbO3 particles: (A) 30%; (B) 40%; (C) 50%; (D) 60%.

**Figure 8.** FE–SEM of surface of CbNN composites with the respective volume fraction of NaNbO3 particles: (A) 30%; (B) 40%; (C) 50%; (D) 60%.

Perovskite-Based Mesostructures and Related Composites — Influence Exerted by Morphology and Interface http://dx.doi.org/10.5772/60654 71

**Figure 9.** FE–SEM of surface of FbNN–PAni*rep* composites with the respective volume fraction of NaNbO3 particles of: (A) 30%; (B) 40%.

## **3.4. Composite characterization**

Figure 7, 8 and 9 show the FE–SEM images of the composite sample. The distribution of the ceramic particles in the polymer matrix likewise the difference between the samples surface according to the increase in the ceramic particles can be observed. The inhomogeneity of the sample with 60% of ceramic particles led to the lowest flexibility of the composite owing to the

**Figure 7.** FE–SEM of surface of FbNN composites with the respective volume fraction of NaNbO3 particles: (A) 30%;

**Figure 8.** FE–SEM of surface of CbNN composites with the respective volume fraction of NaNbO3 particles: (A) 30%;

high concentration of particles and the change in connectivity.

70 Ferroelectric Materials – Synthesis and Characterization

(B) 40%; (C) 50%; (D) 60%.

(B) 40%; (C) 50%; (D) 60%.

To carry out the electric measurements, a contact was deposited onto both sides of the samples; gold electrodes with 1.0 cm of diameter were vacuum evaporated. The composite films were poled with an electric field of 5 MV/m at 90°C during 60 minutes in silicone oil.

A TREK high-voltage power supply was used for the poling process. By measuring the longitudinal piezoelectric coefficient *d*33, the piezoelectric activity of the composite was studied. In order to acquire the longitudinal piezoelectric coefficient *d*<sup>33</sup> Pennebaker Model 8000Piezo d33 Tester was used (American Piezo Ceramics Inc) coupled to a multimeter 34401A (Hewlett Packard).

To avoid problems with lack of uniformity of the composites, the measurements were made at least in 10 different points for each sample, where the average value of these points was taken as the coefficient *d33*.The sample with 50% and 60% of ceramic particles could not be poled because it got ruptured during the polarization process due to the high electric field applied. The improvement in the piezoelectric coefficient is proportional to the anisotropy of the NaNbO3 particles and the volumetric ratio of the ceramic particles was found to scatter in the polymeric matrix. The values of *d*33 obtained for the composites containing NaNbO3 particles are listed in Table 2.


**Table 2.** The values of *d*33 found for the composite with NaNbO3 obtained in different conditions.

Table 3 shows the values of *d*<sup>33</sup> piezoelectric constant for some ceramic/polymer composites. It is possible to observe that for the lowest volumetric ratio of ceramic in the composites, the piezoelectric response for the composite with the ceramic particle covered with PAni (FbNN– PAni rep/PVDF composite) was found to be better than almost all the composites with the same volumetric fraction of ceramic. This value is only smaller than that of PZT/PAni/PVDF composite.


\*Sample poled at different temperatures; \*\*Sample in different electric field

**Table 3.** The values of *d*33 found for some composites in the literature.

Malmonge et al verified the increase in *d*33 as a consequence of the increase in temperature and electric field used for the poled PHB–PZT composite (PHB = poly-β-hydroxybutyrate), indicating the possible application of the composite in areas related to sensors [34].

Hysteresis loop provides information about the remnant polarization (P*r*) of the composites. The P*r* values were obtained using a Radiant Technologies Inc RT 6000 HVS High Voltage Test System. The measurements were carried out at room temperature using varying electric fields (100 and 600 V) and frequencies (2.5 Hz, 5 Hz, 20 Hz and 40 Hz). The FbNN and CbNN (containing 30% and 60% volumetric fraction of ceramic) and FbNN–PAni*rep* with 30% are graphically represented by hysteresis loop, Figures 10, 11 and 12.

The increase in voltage applied provides higher values of electric field; and for the samples with a greater thickness, the electric field value is found to decrease. The increase ob‐ served in the P*r* is proportional to the increase of voltage applied and to the decrease in frequency. Low frequency promotes the increasing of P*r* value and the rounding of hysteresis loop to the same conditions. This happens as a result of the longer cycle times and the longer relaxation time for different charge carriers and dipoles. This can be explained by the fact that some charges are able to follow the electric field whereas other charges are not. There are charges that need longer relaxation time. The increase in the volumetric fraction of the ceramic leads to a higher P*r* value, though with the demerit of having a lower flexibility of composite. In the FbNN–PAni*rep*, the presence of a conduct‐ ing polymer is found to improve the P*r* value. Another factor that improves the P*r* value is the anisotropy of the particles because it is possible to observe that for the FbNN compo‐ sites all the P*r* values are better than the ones for the CbNN composites.

Perovskite-Based Mesostructures and Related Composites — Influence Exerted by Morphology and Interface http://dx.doi.org/10.5772/60654 73

**Figure 10.** *P-E* loops for FbNN composites. (Applied voltage: 100 and 600 V)

Table 3 shows the values of *d*<sup>33</sup> piezoelectric constant for some ceramic/polymer composites. It is possible to observe that for the lowest volumetric ratio of ceramic in the composites, the piezoelectric response for the composite with the ceramic particle covered with PAni (FbNN– PAni rep/PVDF composite) was found to be better than almost all the composites with the same volumetric fraction of ceramic. This value is only smaller than that of PZT/PAni/PVDF

> PZT/PHB [34] 30 1.0 to ~3.2\* PZT/PHB [34] 30 ~1.0 to 4.0\*\*

PZT/PAni/PVDF [15] 30 16 PZT/PVDF [35] 30 4.5 BT/PVDF [36] 30 4.2 BT/PVDF [36] 50 5.5

Malmonge et al verified the increase in *d*33 as a consequence of the increase in temperature and electric field used for the poled PHB–PZT composite (PHB = poly-β-hydroxybutyrate),

Hysteresis loop provides information about the remnant polarization (P*r*) of the composites. The P*r* values were obtained using a Radiant Technologies Inc RT 6000 HVS High Voltage Test System. The measurements were carried out at room temperature using varying electric fields (100 and 600 V) and frequencies (2.5 Hz, 5 Hz, 20 Hz and 40 Hz). The FbNN and CbNN (containing 30% and 60% volumetric fraction of ceramic) and FbNN–PAni*rep* with 30% are

The increase in voltage applied provides higher values of electric field; and for the samples with a greater thickness, the electric field value is found to decrease. The increase ob‐ served in the P*r* is proportional to the increase of voltage applied and to the decrease in frequency. Low frequency promotes the increasing of P*r* value and the rounding of hysteresis loop to the same conditions. This happens as a result of the longer cycle times and the longer relaxation time for different charge carriers and dipoles. This can be explained by the fact that some charges are able to follow the electric field whereas other charges are not. There are charges that need longer relaxation time. The increase in the volumetric fraction of the ceramic leads to a higher P*r* value, though with the demerit of having a lower flexibility of composite. In the FbNN–PAni*rep*, the presence of a conduct‐ ing polymer is found to improve the P*r* value. Another factor that improves the P*r* value is the anisotropy of the particles because it is possible to observe that for the FbNN compo‐

indicating the possible application of the composite in areas related to sensors [34].

*d33* **(pC/N)**

**Composites Volumetric fraction of ceramic (%)**

\*Sample poled at different temperatures; \*\*Sample in different electric field

graphically represented by hysteresis loop, Figures 10, 11 and 12.

sites all the P*r* values are better than the ones for the CbNN composites.

**Table 3.** The values of *d*33 found for some composites in the literature.

composite.

72 Ferroelectric Materials – Synthesis and Characterization

The solid materials are classified according to their ease of conducting electrical current. When they have low conductivity in the range of 10–14 to 10–10 Ω-m, they are classified as insulators; semiconductors have conductivity between 10–9 and 10–1 Ω-m; besides, a conductive material has conductivity higher than 102 Ω-m [37].

The characterization of composite materials indicates that conductivity is of essential relevance owing to the fact that there are multimodal microstructures and each phase has intrinsic properties which determine the properties as well as the applications of the composite.

Considering that the union of the different phases occurs only by physical contact of the surfaces, known as interfaces, no chemical bond formation is observed. Therefore, the layers that form the composite (matrix/disperse phase) can be said to retain their distinct conductivity.

The heterogeneity of microstructure consists of single phase regions which are statistically distributed in the volume of composite, and the macroscopic properties of the composite that are directly connected to this distribution [38]. In the composite preparation method and in the volumetric fraction of each phase there are parameters which directly influence the resulting properties. The influence of each phase in the composite characteristics is associated with the intrinsic characteristics. The volume fraction of the disperse phase (one perovskite oxide) and the composites matrix which is an insulating polymer, is dependent on the

**Figure 11.** *P-E* loops for CbNN composites. (Applied voltage: 100 and 600 V)

**Figure 12.** *P-E* loops for FbNN–PAni*rep* composite. (Applied voltage: 100 and 600 V)

embedded oxide fraction in the polymer matrix. Depending on the process, it can be isolated or connected to the polymer. The percolation transition phenomenon, commonly known as the percolation threshold, occurs during the transition from the isolated oxide behavior to the interconnected oxide behavior. The percolation threshold is a mathematical term related to the percolation theory which involves long-range bond formation in a random system. Below the limit, the component or system as a whole is not connected, and over the limit there is a greatness component that is bigger than the system itself and which exerts influence on the overall behavior of the composite. The presence of a metal as a dispersed phase in the polymer matrix paves the way for the occurrence of an insulator/conductor interface transition [39].

Close to the percolation threshold, the value of the electrical conductivity and the dielectric constant of the composite increases abruptly in several orders of magnitude. However, the composite type insulator/semiconductor presents a remarkable increase in the dielectric constant with high values and a relatively low conductivity range, close to the percolation threshold [40].

The actual conductivity of the material is directly proportional to the interaction between the dispersed phase and the matrix phase expressed through the power law (a functional rela‐ tionship between two quantities, where one varies as potency of the other). Mathematically, the effective conductivity (σ) or the effective dielectric constant (ε) of the composite is described by the following equations [38,40].

$$
\sigma\_{\rm eff} = \sigma\_f \left( f\_f - f\_c \right)^t, \text{ to } f\_f > f\_c \tag{6}
$$

$$
\sigma\_{\rm eff} = \sigma\_{\rm PVDF} \left( f\_c - f\_f \right)^{-s}, \text{ to } f\_f < f\_c \tag{7}
$$

$$\mathfrak{e}\_{\text{eff}} = \mathfrak{e}\_f \left( f\_f - f\_c \right)^{\cdot \cdot}, \text{ to } f\_f > f\_c \tag{8}$$

$$
\varepsilon\_{\rm eff} = \varepsilon\_{\rm PVDF} \left( f\_c - f\_f \right)^{-s^\*}, \text{to } f\_f < f\_c \tag{9}
$$

where **ff** is the fraction of the disperse phase; **fc** is the percolation threshold; **σf** the conductivity of the dispersed phase; **σPVDF** and phase conductivity matrix (PVDF); **ε<sup>f</sup>** the dielectric constant of the disperse phase and **εPVDF** the dielectric constant of the matrix phase. The **t** e **s** exponents are the critical values of the conductive region and the insulating region. Some articles that have already been published reported that the percolation threshold is influenced by the size, morphology and constitution of particles that form the dispersed phase [41,42]. The composites analyzed in this study consist of PVDF, as polymer matrix phase and NaNbO3 as dispersed phase. The chemical composition and crystal structure of the dispersed phase are fixed, though we have two distinct particle morphology – cubes and fibers.

embedded oxide fraction in the polymer matrix. Depending on the process, it can be isolated or connected to the polymer. The percolation transition phenomenon, commonly known as the percolation threshold, occurs during the transition from the isolated oxide behavior to the interconnected oxide behavior. The percolation threshold is a mathematical term related to the percolation theory which involves long-range bond formation in a random system. Below the limit, the component or system as a whole is not connected, and over the limit there is a

**Figure 11.** *P-E* loops for CbNN composites. (Applied voltage: 100 and 600 V)

74 Ferroelectric Materials – Synthesis and Characterization

**Figure 12.** *P-E* loops for FbNN–PAni*rep* composite. (Applied voltage: 100 and 600 V)

To calculate the percolation threshold of the composites, the measurements of electrical conductivity and dielectric constant at 1 kHz for the various rates (matrix / dispersed phase) were carried out.

Figure 13 shows the curves of dielectric constant and conductivity measurements for the CbNN/PVDF composite, where one can observe that there is an abrupt increase in both dielectric constant and conductivity as the ratio is higher than 50% (w/w) for the cubes morphology. Equation 9 jointly with the best linear fit (in the illustrated set) with the value of s = 0.31 +/– 0.08 allow us to indicate that the percolation mechanism (percolation threshold) in this composite and for these processing conditions occur at the rate of 54.6% (w/w). In Figure 13, the threshold value is close to the abrupt increase in conductivity. The composites when subjected to an electric field responded to the field applied accumulating charges on the surface of particles; this charge interferes in the characteristics of the particles–matrix interfaces. The composites formed by the concentrations of morphologically different particles, where the dispersed phase needs different rates (in the matrix phase) so as to occur an interconnection between them. A minimum distance required between the particles prior to the occurrence of percolation is known as interconnection [43]. When the morphology of the particle is in the form of cubes, the distance must be very small in order to promote the contact between them since polarization is homogeneous in the cube–matrix interfaces. Thus, for cubes-like particles a high density of ceramics in the array is required to achieve the interfacial polarization needed to promote the percolation threshold for 54.6% (w/w) of the cubes in the matrix. The variation of dielectric constant and conductivity values prior to the percolation threshold, as can be observed at 40% (w/w), can be linked to the interfacial polarization and the percolation paths in the matrix [44].

**Figure 13.** Dielectric constant and conductivity for the various fractions mass of cubes dispersed phase in PVDF ma‐ trix. Inset for the best linear fit of the percolation threshold.

The dielectric constant and conductivity values for the FbNN/PVDF composite are illustrated in Figure 14; in this case, there is an abrupt increase in conductivity after 30% (w/w) of fibers. Applying the best linear fit (shown in the inset) with s = 0.90 +/– 0.05 in equation 9 gives you a concentration of 38.0% (w/w) for the percolation threshold. Therefore, the morphology of the fibers, nanoparticles 1D, allows the polarization to reach a long distance over the length of the fiber. A lower concentration of particles enables the interconnection between them so the percolation threshold occurs at only 38% (w/w).

Perovskite-Based Mesostructures and Related Composites — Influence Exerted by Morphology and Interface http://dx.doi.org/10.5772/60654 77

Figure 13 shows the curves of dielectric constant and conductivity measurements for the CbNN/PVDF composite, where one can observe that there is an abrupt increase in both dielectric constant and conductivity as the ratio is higher than 50% (w/w) for the cubes morphology. Equation 9 jointly with the best linear fit (in the illustrated set) with the value of s = 0.31 +/– 0.08 allow us to indicate that the percolation mechanism (percolation threshold) in this composite and for these processing conditions occur at the rate of 54.6% (w/w). In Figure 13, the threshold value is close to the abrupt increase in conductivity. The composites when subjected to an electric field responded to the field applied accumulating charges on the surface of particles; this charge interferes in the characteristics of the particles–matrix interfaces. The composites formed by the concentrations of morphologically different particles, where the dispersed phase needs different rates (in the matrix phase) so as to occur an interconnection between them. A minimum distance required between the particles prior to the occurrence of percolation is known as interconnection [43]. When the morphology of the particle is in the form of cubes, the distance must be very small in order to promote the contact between them since polarization is homogeneous in the cube–matrix interfaces. Thus, for cubes-like particles a high density of ceramics in the array is required to achieve the interfacial polarization needed to promote the percolation threshold for 54.6% (w/w) of the cubes in the matrix. The variation of dielectric constant and conductivity values prior to the percolation threshold, as can be observed at 40% (w/w), can be linked to the interfacial polarization and the percolation paths

**Figure 13.** Dielectric constant and conductivity for the various fractions mass of cubes dispersed phase in PVDF ma‐

The dielectric constant and conductivity values for the FbNN/PVDF composite are illustrated in Figure 14; in this case, there is an abrupt increase in conductivity after 30% (w/w) of fibers. Applying the best linear fit (shown in the inset) with s = 0.90 +/– 0.05 in equation 9 gives you a concentration of 38.0% (w/w) for the percolation threshold. Therefore, the morphology of the fibers, nanoparticles 1D, allows the polarization to reach a long distance over the length of the fiber. A lower concentration of particles enables the interconnection between them so the

trix. Inset for the best linear fit of the percolation threshold.

percolation threshold occurs at only 38% (w/w).

in the matrix [44].

76 Ferroelectric Materials – Synthesis and Characterization

**Figure 14.** Dielectric constant and conductivity for the various fractions mass of fibers dispersed phase in PVDF ma‐ trix. Inset for the best linear fit of the percolation threshold.

Figure 15 presents the data obtained by plotting the dielectric constant and conductivity for the composite FbNN–PAni*rep*/PVDF. The abrupt increase in the dielectric constant and conductivity values is observed from the first analyzed concentration of 30% (w/w). Because of this, it is believed that the percolation threshold is set to a lower concentration. Comparing the three types of dispersed phase of this review, this is the one with the lowest value of percolation threshold, which can be explained by the surface characteristics. The particle morphology 1D indicates a behavior similar to that seen in Figure 14; however, the covering of the fibers with polyaniline which promotes conductivity and the connectivity allowing the percolation threshold is reached with lower concentrations of the dispersed phase. Therefore, to establish the percolation threshold of the composites, a study involving the minor fractions dispersed phase is required. There is also an anomalous behavior observed in Figure 15, for the concentration of 50% (w/w) of dispersed particles. At this point, the results of conductivity and dielectric constant are 1.1x10–8 and 4.0, respectively. These values are close to those of pure PVDF matrix. This anomalous behavior for the concentrations above the percolation threshold has been observed in some papers that have been published already [41,45,46]. It is suggested that there is a formation of agglomerates with dispersed phase which are found to be isolated functioning as microcapacitors, enveloped by an insulating film that prevents both the load passage and a continued polarization of the network, so a decrease in the dielectric constant and conductivity is verified at this concentration.

The dielectric constant and conductivity values for the dispersed phases and for the pure PVDF are plotted in Figure 16. These values were measured in pellet of these materials. The values of electric conductivity are low contrary to the dielectric constant values which are found to be high. The dielectric constant and conductivity increase in the following order PVDF< cubes< fibers< fibers–PAni*rep*, which can be explained by the fact that this polymer is an insulating material with a rigid structure linked by strong covalent bonds, which can generate a polari‐ zation though with difficulty resulting in very low dielectric constant and conductivity. Interestingly, the dispersed phase, which are perovskite oxides, have dipoles in their crystal‐ line structure, making them capable of being oriented quite more easily.

**Figure 15.** Dielectric constant and conductivity for the various fractions mass of fibers–PAni*rep* dispersed phase in PVDF matrix. Inset for the best linear fit of the percolation threshold.

**Figure 16.** Dielectric constant and conductivity for pure PVDF matrix and the dispersed phase, NaNbO3 with different morphology (cubes, fiber and fiber–PAni*rep*).

The morphology of the dispersed phase directly influences this behavior; the fibers compared with cubes as shown in Figure 16 allow for better charge distribution and thus a higher conductivity. The surface-modified fibers with a conductive polymer, in this case PAni, promote conductivity and permittivity (dielectric constant). The values found for the dielectric constant and conductivity decrease in the order fibers–PAni*rep*, fiber, cubes. The same result is observed for the percolation threshold values, when these materials are used as the dispersed phase in the PVDF matrix, indicating that these factors are interrelated.

### **4. Conclusion**

By microwave hydrothermal synthesis, it is possible to obtain Na2Nb2O6.nH2O and NaNbO3 orthorhombic crystalline structure particles. The Na2Nb2O6.nH2O is obtained in fiber-like morphology while NaNbO3 presented cubic-like morphology. The results are associated to synthesis conditions including synthesis time and microwave power. Using 300 W, the increase in synthesis time favors the formation of NaNbO3; and by 800 and 1000 W the NaNbO3 is obtained within a relatively shorter time. The Na2Nb2O6.nH2O is used as a precursor to get a fiber-shaped NaNbO3. The thermal treatment of Na2Nb2O6.nH2O promotes the dehydration and the formation of 1D NaNbO3. The characteristics of the particles exert influence on the material characteristics. Both morphologies of NaNbO3 particles can be mixed with PVDF for the production of flexible composites. An increase in the amount of the ceramics particles leads to the loss of flexibility in the composite owing to the change of connectivity of the ceramic particles and polymer. The anisotropy of ceramic particles improves the composites charac‐ teristics, such as d33, Pr, conductivity and dielectric constant values. By inserting a third phase into the composite, these values tend to be higher. The characterization of composite materials indicates the importance of conductivity due to the fact that these materials have multimodal microstructure and each phase has intrinsic properties that determine the properties and applications of the composite formed. These preliminary results demonstrate that the NaNbO3 composite can be used with piezoelectric and ferroelectric properties depending on the material.
