Effect of Bismuth Ferrite Nanoparticles on Physicochemical Properties of Polyvinylidene Fluoride-Based Nanocomposites

Abstract

Bismuth ferrite (BiFeO₃, BFO) is one of the few single-phase crystalline compounds exhibiting strong multiferroic properties at room temperature, which makes it promising for use in various fields of science and technology. The remarkable characteristics of BFO at the nanoscale position it as a compelling candidate for enhancing the functionalities of polymeric nanocomposite materials. In this study, we explore the fabrication of polyvinylidene fluoride (PVDF) nanocomposites with a variable content of BFO nanopowders (0, 5, 10, 15, 20, and 25 wt%) by solution casting in the form of thin films with the thickness of ~60 µm. Our findings reveal that the presence of BFO nanoparticles slightly facilitates the formation of β- and γ-phases of PVDF, known for their enhanced piezoelectric properties, thereby potentially expanding the utility of PVDF-based materials in sensors, actuators, and energy harvesting devices. On the other hand, the increase in filler concentration leads to enlarged spherulite diameter and porosity of PVDF, as well as an increase in filler content above 20 wt% resulting in a decrease in the degree of crystallinity. The structural changes in the surface were found to increase the hydrophobicity of the nanocomposite surface. Magnetometry indicates that the magnetic properties of nanocomposite are influenced by the BFO nanoparticle content with the saturation magnetization at ~295 K ranging from ~0.08 emu/g to ~0.8 emu/g for samples with the lowest and higher BFO content, respectively.

1. Introduction

Bismuth ferrite (BiFeO₃, BFO) stands out for its unique property of simultaneously exhibiting ferromagnetic and ferroelectric characteristics, resulting in remarkable multiferroic properties at room temperature [1,2,3,4]. This exceptional feature renders BFO an attractive candidate for integration into a wide range of devices such as memory storage, sensors, and actuators. Moreover, nanostructured BFO has been shown to possess pronounced piezocatalytic [1,2,3], photocatalytic [4,5,6], and photovoltaic [7,8,9] properties. However, the practical application of BFO nanostructures is hindered by challenges in processing and maintaining properties, particularly in thin films.

In this context, polymer-based nanocomposites emerge as promising candidates that can retain the unique properties of BFO and at the same time have a positive effect on the properties of the polymer matrix [5,10,11]. Polymer-based nanocomposites offer advantages such as light weight, corrosion resistance, flexibility, relatively low cost, and an easy manufacturing process [12]. Polyvinylidene fluoride (PVDF), a long-chain semicrystalline polymer with a repeating unit in the form of [-CH2-CF2-]n, and its copolymers have attracted attention due to their piezoelectric [13,14,15,16], pyroelectric [13,14,15,16,17,18], and ferroelectric [13,14] properties when in an electroactive phase, such as the β- or γ-phase. The combination of BFO nanoparticles and PVDF polymer matrix into a single nanocomposite yields a material with enhanced functional properties.

The versatility of PVDF-based BFO nanocomposites extends to a wide range of applications including piezoelectric [19,20], ferroelectric, dielectric, and mechanical energy-harvesting devices, as well as self-powered electronic devices [21,22]. Additional applications include memory storage devices [23], capacitors [20,24,25], spintronics [11,21,24], piezoelectric and stress sensors [19,24], sonolysis and photolysis [26], piezocatalysis, photocatalysis, and piezophotocatalysis [23,27].

It is important to note the synergism of these structures, where both components of the nanocomposite mutually influence each other’s properties. For instance, Alekhika Tripathy et al. [11] synthesized BFO nanoparticles by a hydrothermal method and incorporated them into poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] and poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)] copolymer matrices. The BFO nanoparticles acted as nucleating agents inside the polymer matrix, thereby improving the formation of polar β-phase, particularly with ~6 wt% BFO content. The resulting nanocomposite film P(VDF-TrFE)/BFO exhibited superior piezoelectric performance and was utilized in the fabrication of a flexible piezoelectric nanogenerator capable of generating a maximum of 18.5 V under a biomechanical finger tapping force. Similarly, Sonali Pradhan et al. [24] successfully fabricated nanocomposites of BFO nanoparticles in a P(VDF-TrFE) matrix obtained in the form of films with enhanced ferroelectric contour and low dielectric losses, proposed for use in sensor applications.

Moreover, the polymer matrix can serve as a support for particles, enhancing their reusability, particularly in catalysis and water remediation applications. This addresses concerns regarding secondary pollution due to material dispersion within the environment. Wafa Amdouni et al. [5] observed exceptional efficacy in degrading rhodamine B model dye, achieving record degradation rates when piezocatalysis was synergistically combined with sunlight photocatalysis. This was achieved using 60 nm BFO particles embedded in a P(VDF-TrFE) matrix, resulting in flexible, chemically stable, and recyclable nanocomposites that retain remarkable piezophotocatalytic performance. While PVDF-based BFO nanocomposites hold promise for numerous applications, fabrication methods for such nanocomposites are still under development, and many physicochemical properties remain unexplored.

In this work, we synthesized BFO nanoparticles via a glycine-based sol–gel route and investigated their concentration effect on the structural, surface, and magnetic properties of PVDF. Particular attention was paid to the influence of nanofiller content on the morphology of the polymer matrix and the hydrophobicity of the nanocomposite surface—aspects that, to the best of our knowledge, have not been thoroughly explored in previous studies.

2. Experimental Methodology

2.1. Materials

The following chemicals were used as received: bismuth nitrate pentahydrate Bi(NO₃)₃ × 5H₂O (≥98%; LenReactiv, Saint Petersburg, Russia), iron nitrate (III) nonahydrate Fe(NO₃)₃ × 9H₂O (≥98%; LenReactiv, Saint Petersburg, Russia), sodium hydroxide NaOH (≥98%; LenReactiv, Saint Petersburg, Russia), glycine H₂NCH₂COOH (≥99%; PanReac AppliChem, Chicago, IL, USA), nitric acid HNO₃ (≥99%; Gala-Trade, Saint Petersburg, Russia), polyvinylidene fluoride (PVDF; m.w. 534,000; Sigma-Aldrich, St. Louis, MO, USA), N,N-dimethylformamide (DMF; ≥98%; Ekos-1, Moscow, Russia). Distilled water H₂O(d) was used in all synthesis.

2.2. Synthesis of BFO Nanoparticles

Nanoscale BFO particles were synthesized by the glycine-based sol–gel method [28] (Figure 1). The synthesis process commenced with the preparation of precursor solutions in separate vials, where 1.1 mmol of bismuth nitrate was dissolved in 10.5 mL H₂O(d) to yield a milky solution, and 1 mmol of iron (III) nitrate in 10 mL H₂O(d) to produce a bright orange solution. The metal cations were taken in a ratio of 1.05:1 (Bi:Fe) to avoid a lack of bismuth. For better dissolution of precursors, a laboratory vortex (Vortex V-1 plus) was used.

The resulting highly concentrated solutions were mixed for 15 min at 80 °C, following which 2.1 mol of glycine was added, and the reaction mixture was stirred for additional 15 min at 80 °C. Subsequently, 1.5 mL of HNO₃ (65%) was introduced to the mixture. After complete dissolution, the mixture was evaporated on a hotplate at 150 °C for an hour. The temperature was then raised to 330 °C to complete the self-combustion reaction, yielding a fluffy powder product. The final powder was annealed in a muffle furnace (LOIP Ltd., Saint Petersburg, Russia) at 550 °C for 1.5 h in air.

2.3. Fabrication of BFO/PVDF Nanocomposites

The nanocomposites were prepared using the solvent casting method assisted with the Dr. Blade technique, also known as knife coating or blade coating. The procedure of nanocomposite sample preparation was adapted from [29] and is illustrated in Figure 2. In brief, to produce polymer films, PVDF powder was dissolved in DMF with continuous stirring. Subsequently, BFO nanoparticles in DMF, previously exposed to ultrasound, were added to the resulting mixture to form nanocomposite films. After intensive stirring, the mixture was poured under the blade of a squeegee knife to produce films. The thickness of the films was controlled by adjusting the gap between the blade and the support [30]. The resulting films were dried in a desiccator for 24 hours at 60 °C. Thus, a series of nanocomposite films with a fixed thickness of 60 µm and various BFO filler contents (f_BFO) of 0 (pure PVDF), 5, 10, 15, 20, and 25 wt% was prepared (

Table 1. Characteristics of BFO/PVDF nanocomposites and pure PVDF film: nominal content of BFO particles (f_BFO), content of β and γ phases (F(β + γ)), degree of crystallinity (x_c), average spherulite diameter (Dspherulite), and average pore diameter (Dpore).

Sample	fBFO (wt%)	$\mathit{F}\mathbf{(}\mathsf{\beta }+\mathsf{\gamma }\mathbf{)}$ (%)	${\mathit{x}}_{\mathit{c}}$ (%)	Dpore $\mathbf{(}\mathsf{\mu }$m)	Dspherulite $\mathbf{(}\mathsf{\mu }$m)
PVDF	0	61.6	27 ± 3	7 ± 1	8 ± 1
5BFO	5	61.8	29 ± 3	8 ± 1	11 ± 1
10BFO	10	61.7	28 ± 3	8 ± 1	14 ± 1
15BFO	15	62.2	29 ± 3	12 ± 1	15 ± 2
20BFO	20	64.5	28 ± 3	14 ± 2	17 ± 2
25BFO	25	64.9	20 ± 3	15 ± 2	17 ± 2

).

3. Characterization Methods

3.1. X-ray Diffraction (XRD) Analysis

X-ray diffraction analysis (XRD) was performed using an AXRD Benchtop powder diffractometer (Proto Mfg. Ltd., LaSalle, ON, Canada) with monochromatic radiation Cu-Kα₁ λ = 1.540562 Å. The average coherent scattering region (D) was calculated using the Scherrer formula [31]:

$$D={\displaystyle \frac{0.94 \mathsf{\lambda }}{\beta cos\theta }} ,$$

(1)

where β is the full width at half the maximum, estimated after fitting the peaks using the Voigt function, and θ is the Bragg angle.

3.2. Transmission Electron Microscopy (TEM)

Transmission electron microscopy (TEM) images and selected area electron diffraction (SAED) patterns of synthesized BFO nanostructures were taken on the JEOL JEM-1400 (120 kV) microscope (Tokyo, Japan). All samples were prepared by dropping dichloromethane dispersion of synthesized samples onto a carbon-coated copper grid (300 mesh) and subsequently evaporating the solvent.

3.3. Fourier-Transform Infrared Spectroscopy (FTIR)

The phase formation in PVDF with BFO loading was also proved using Fourier-transform infrared spectroscopy (FTIR). The PerkinElmer Spectrum 65 (Waltham, MA, USA) was used to perform these measurements. A square piece measuring approximately 3 × 3 mm was cut from each nanocomposite material and then analyzed using attenuated total reflectance (ATR) within the wavelength range of 4000 cm⁻¹ to 600 cm⁻¹. The samples were deposited on a diamond prism with a high refractive index. The content of the electrically active (β and γ) phases is determined from Equation (2) [32]:

$$F\left(\mathsf{\beta }+\mathsf{\gamma }\right)={\displaystyle \frac{A_{\mathsf{\beta },\mathsf{\gamma }}}{1.26A_{\mathsf{\alpha }}+A_{\mathsf{\beta },\mathsf{\gamma }}}}$$

(2)

where $A_{\mathsf{\beta },\mathsf{\gamma }}$ and $A_{\mathsf{\alpha }}$ are absorbance values at 763 cm^–1 and 840 cm^–1, respectively.

3.4. Differential Scanning Calorimetry (DSC)

The degree of crystallinity of the finished nanocomposites was evaluated on a differential scanning calorimeter (DSC, NETZSCH 204 F1 Phoenix, Selb, Germany) by comparing the melting heat of the sample and pure crystalline PVDF (104.6 J/g) [28,30,33]. The samples were analyzed between room temperature and 350 °C at a heating or cooling rate of 5 °C/min under an argon atmosphere. The degree of crystallinity ($x_c$) was calculated from the sample’s fusion heat (${∆H}_f$) with Equation (3) [32]:

$$x_c\left(\%\right)={\displaystyle \frac{∆H_f}{∆{H_f}^0}}·100\%$$

(3)

where $∆{H_f}^0$ is the enthalpy for 100% crystalline form of PVDF.

3.5. Thermogravimetric Analysis (TGA)

Thermogravimetric analysis (TGA) was conducted using a LABSYS evo instrument (Seratam company, Caluire, France). Approximately 10 mg of each sample was placed in an alumina crucible and subjected to analysis in the temperature range of 18–900 °C in the air environment. The data were obtained after the blank subtraction, to remove the crucible contribution on weight loss values. The value obtained at 400 °C was used as the initial mass for normalization of the nanocomposites and the PVDF film to ensure a consistent baseline for comparison across different samples.

3.6. Scanning Electron Microscopy (SEM)

Scanning electron microscopy (SEM, Hitachi TM4000 Plus, Tokyo, Japan) in electron backscattering mode was used to study the surface morphology of polymer films, particles, and particle distribution on the surface. The 5 × 5 mm samples were attached to carbon tape and the accelerating voltage was 30 kV.

3.7. Contact Angle (CA) Analysis

The contact angle (CA, θc) is the angle between the surface of a liquid and a solid surface at the point of contact of these phases. Quantitatively, this value characterizes the wettability, which was used in relation to BFO/PVDF nanocomposites. The CA was measured by a contact angle meter Attension Theta (Biolin Scientific, Stockholm, Sweden). Ultrapure water was chosen as the probe liquid in the experiments. A water drop (30 μL) was lowered onto the sample’s surface from a needle tip. A magnified image of the droplet was recorded using a digital camera. Static CA was determined from these images with the calculation software OneAttension v. 4.1 (Biolin Scientific, Stockholm, Sweden). The CA measurement was taken as the mean value of 3 different points on each sample.

3.8. Vibrating-Sample Magnetometer (VSM) Analysis

The field dependence of magnetization M(H) of nanocomposites was measured using a vibrating-sample magnetometer (VSM, Lakeshore 7400 System, Westerville, OH, USA) at room temperature (~295 K). The law of approach to saturation (LAS) was used to estimate the saturation magnetization (Ms) [34,35]:

$$M\left(H\right)=M_s·\left(1-{\displaystyle \frac{A}{H}}-{\displaystyle \frac{B}{H^2}}\right),$$

(4)

where A and B are the free fitting parameters.

4. Results and Discussion

4.1. BiFeO₃ Nanoparticle Characterization

Figure 3a shows a TEM micrograph of BFO nanoparticles. The recorded SAED pattern (Figure 3b) confirms the formation of a distorted rhombohedral structure of BiFeO₃. The data obtained were compared with ICSD 01-086-1518 (Figure 3c). The XRD pattern of the BFO powder sample (Figure 3d) aligns with the pattern expected for the rhombohedral structure of BiFeO₃ (space group R3c) with negligible content of satellite phases (less than 3%). The average crystallite size (D_XRD) of BFO particles, evaluated using Equation (1), was determined to be ~20 nm.

The field dependence of magnetization was investigated at ~295 K (Figure 3e). The BFO nanoparticles exhibit a value of M_S, estimated with Equation (4), of ~0.5 emu/g, which can be ascribed to the uncompensated magnetic moment of the G-type antiferromagnetic BiFeO₃ [36,37]. The observed S-shape M(H) dependence and high paramagnetic-like slope near room temperature are consistent with previous observations in BFO nanoparticles synthesized via the sol–gel method [38].

4.2. BFO/PVDF Nanocomposite Characterization

4.2.1. Structural Characterization of Nanocomposites

The XRD patterns for BFO/PVDF nanocomposites and pure PVDF film are shown in Figure 4. The XRD analysis confirms the presence of both constituents—polymer and BFO nanoparticles—in the nanocomposites. The intensity of the reflexes related to each constituent agrees with the concentration, indicating the successful incorporation of BFO nanoparticles into the PVDF matrix. Distinguishing between the XRD peaks of PVDF phases is not trivial. According to [26], the α-, β-, and γ-phases of PVDF exhibit an intense reflex near 20° in XRD patterns. However, the α- and β-phases are characterized by additional distinct reflexes. In our patterns, reflexes corresponding to α- and β-phases are discernible, while the presence of the γ-phase is uncertain. To gain a better understanding of the electroactive β- and γ-phase content, further analysis using FTIR was performed (see Section 4.2.2).

According to XRD analysis, the BFO particles with R3c symmetry undergo a structural change after compounding, passing into tetragonal form with the P4mm symmetry (COD 00-101-0021). Previously, this change in symmetry has been observed in BFO thin films grown on different substrates, where different microstresses lead to the formation of BFO structures with different symmetries, including a combination of rhombohedral (R3c) and tetragonal (P4mm) structures [39]. In our case, this can be caused by the macromolecular diffusion in the ultrasound treatment in DMF and its further evaporation during nanocomposite fabrication. For instance, changes in the structure of α-Fe₂O₃ nanoparticles were observed earlier after exposure to ultrasound [40]; at the same time, the symmetry of those particles remained the same—only the interplanar distance changed, which clearly shifted the peaks to the lowest angles. In another study [41], BFO particles changed symmetry under the influence of reduced graphene oxide (rGO). The glycine used as a fuel in this sol–gel process may be a source of carbon structures.

It is worth noting that previous studies have reported that the structure of BFO nanoparticles, synthesized using a very similar method and incorporated within PVDF using a solvent casting method but with a different solvent, remained unchanged after compounding [26]. This suggests that the solvent and processing conditions may play a role in the structural changes observed. Further research and analysis are needed to fully understand the structural changes and their impact on the properties of BFO in the PVDF matrix. We note that BFO in the P4mm phase exhibits a larger polarization compared with R3c [42], which could potentially enhance the overall ferroelectric response of nanocomposites.

Figure 5 shows the FTIR absorption spectra of a pure PVDF polymer and a nanocomposite BFO/PVDF. According to [43], the characteristic bands of the α-phase are approximately at 614, 763, 795, 854, 975, 1149, 1209, 1383, and 1423 cm^–1. For the β-phase, they are at about 1275 and 1431 cm^–1, and for the γ-phase, they are at about 776, 811, 833, 1234, and 1429 cm^–1. Peaks around 881, 1071, 1176, and 1401 cm^–1 can be observed for samples with any phase composition.

Analysis of the FTIR spectra enables the distinction of the total content of the β- and γ-phases, referred to hereafter as the electroactive phase content F(β + γ). It was found to be ~62% for the pure PVDF film, with a slight increase to 65% for the sample with the highest BFO content (Table 1). This observation aligns with findings in the literature, where an increase in F(β + γ) for P(VDF-TrFE) from 78% to 82% was noted with the addition of BFO nanoparticles ranging from 0 up to 6 wt% [11]. However, in the study [11], as the weight content of BFO exceeded 6 wt%, the F(β + γ) tended to decrease.

The DSC measurements (Figure 6) show the melting (T_M = 161 ± 1 °C) and crystallization processes (T_C = 136 ± 1 °C). Any significant difference in these temperatures was not detected among the pure PVDF and BFO/PVDF nanocomposite samples.

The degree of crystallinity (x_c) was estimated using the enthalpy of fusion $∆H_f$, calculated as the ratio between the area of the melting peak and the heating rate by substituting into Equation (3). At higher concentrations, BFO particles may agglomerate, potentially decreasing the effective interaction area between nanoparticles and PVDF chains. This phenomenon could lead to a reduction in electroactive phase content and a decrease in crystallinity level. Indeed, we observed that the degree of crystallinity remains relatively stable (around 28–29%) for BFO contents up to 20 wt% but drops to 20 ± 3% for the 25 wt% BFO sample (Table 1).

The TGA conducted in air showed that the weight loss in pure PVDF occurred in a two-step process (Figure 7, dashed line): a sharp decrease in mass at ~475 °C, followed by a second step concluding at ~650 °C, resulting in complete (~100%) weight loss. This two-step degradation process is characteristic of PVDF-based nanocomposites [44]. In the case of the nanocomposites, the weight loss associated with these two processes was proportional to the nominal content of the inorganic BFO nanoparticles, as expected due to the reduction in organic content. The slight increase in temperature during the first step of the degradation process is roughly proportional to the BFO content in the nanocomposite. This can be attributed to the interplay between the organic PVDF matrix and the inorganic BFO nanoparticles, which enhances the stability of the polymer chains. However, the total degradation of the nanocomposites occurs at lower temperatures after the second step. This is explained by the fact that the inorganic fillers may increase the thermal conductivity of the polymer matrix.

Notably, an additional weight loss process was observed at higher temperatures for the nanocomposites, characterized by a gradual decrease in mass. This behavior is attributed to the removal of residual organics or carbonaceous impurities present within the BFO nanoparticles after the sol–gel synthesis process.

4.2.2. Surface Properties of Nanocomposites

According to SEM images, the pure polymer film exhibits a characteristic structure composed of spherulites and pores with characteristic sizes D_pore and D_spherulite, as shown in Figure 8 and detailed in Table 1. These spherulites represent crystalline regions within the polymer matrix, while the pores indicate areas of lower density or voids. Possible causes of pore formation include the air capture during the manufacture of a polymer solution and the release of volatile products (i.e., solvents) during the solidification of the composite. It is worth underlining that the films solidified under the same conditions, yet there is an increase in the number of pores and their diameter with increasing filler concentration. This observation suggests that the BFO particles modify the microstructure of the polymer and as a consequence, the formation of microvoids and increased porosity.

As shown in Table 1, the D_pore increases from 7 ± 1 μm in pure PVDF to 15 ± 2 μm in the 25 wt% BFO sample. Concurrently, the electroactive phase content F(β + γ) shows a slight increase from 61.6% in pure PVDF to 64.9% in the 25 wt% BFO sample. These results indicate that the presence of BFO particles and the resulting porous structure may facilitate the formation of electroactive phases, potentially by providing nucleation sites that promote β- and γ-phase crystallization.

Upon the addition of BFO nanoparticles, the SEM images reveal bright spots uniformly distributed on the surface of the nanocomposite films. With an increase in the nominal concentration of BFO, the number of these particles increases.

CA analysis was performed on BFO/PVDF nanocomposites to investigate the wetting behavior of the surfaces. The contact angle value (θ_c) was measured as a function of increasing filler concentration, and the results are shown in Figure 9. The θ_c ranged from an initial value of 75°, corresponding to pure PVDF, to a maximum value of 89° at a BFO concentration of 20 wt%. At a higher BFO concentration of 25 wt%, the θ_c decreased slightly to 87°, which is within the margin of measurement error. It is important to note that all the obtained contact angle values were within the range of 0° < θ_c < 90°, indicating that the BFO/PVDF nanocomposites exhibit wettable hydrophilic surfaces.

The introduction of BFO contributes to an increase in the hydrophobicity of the PVDF matrix. The increase in hydrophobicity of nanocomposite surface correlates with an increase in the size of pores and spherulites as well as BFO particles exposed to the surface on the nanocomposites with higher filler concentrations, which in turn leads to an increase in surface roughness [45]. The increased roughness provides more sites for interactions, leading to altered surface energy [46]. Thus, the surface roughness generally leads to an increase in θ_c and surface hydrophobicity [47].

4.2.3. Magnetic Properties of Nanocomposites

In the VSM analysis of all nanocomposite samples (Figure 10), we observed S-shaped M(H) curves, where the magnetic behavior was, as expected, driven by the BFO. The M_S value obtained from the analysis ranged from ~0.08 emu/g for samples with the lowest 5 wt% BFO content to ~0.8 emu/g for those with the highest 25 wt% BFO content. This reduction in M_S with lower BFO content can be attributed to the dilution effect of magnetic BFO particles within the diamagnetic PVDF matrix [48]. We also noted a large error in the determination of magnetic characteristics due to the small mass of BFO particles in the investigated nanocomposite thin film samples. The coercivity of all samples was found to be negligible (10 ± 1 Oe), with no dependence on the particle concentration.

5. Conclusions

In conclusion, the development of PVDF/BFO nanocomposites represents a burgeoning area of modern research, with a growing number of published papers attesting to its significance. Figure 11 provides a roadmap of selected studies in this area. While considerable attention has been devoted to exploring various aspects of these nanocomposites, such as their piezoelectric, photocatalytic, and magnetic properties, there remains a notable gap in understanding the specific effect of BFO content on polymer morphology.

In this study, we successfully synthesized BFO particles via the sol–gel method and subsequently incorporated them into the PVDF matrix with various concentrations. The TEM and SAED results confirmed the high crystallinity of the BFO nanoparticles. Interestingly, the XRD pattern of the obtained particles showed almost pure BFO R3c symmetry; however, the processing conditions (ultrasound, drying) could lead to a transition to P4mm symmetry, which was observed for XRD patterns of nanocomposite samples.

The FTIR analysis of nanocomposite films demonstrated an increase in the electroactive phase content, which suggests the improved ferroelectric behavior of the nanocomposites. Magnetic measurements indicated that the nanocomposites exhibit weak ferromagnetism, with the saturation magnetization being influenced by the BFO nanoparticle concentration. This finding suggests the possibility of the application of these nanocomposites in magnetoelectric devices.

SEM analysis of nanocomposite films indicates that an increase in filler concentration leads to an increase in the average diameter of pores and spherulites. Since the latter affects the surface roughness of the films, an increase in the value of the contact angle was observed with the increase in BFO content. Additionally, the observed increase in hydrophobicity with BFO content caused by morphology variation, as determined by contact angle measurements, suggests potential for applications of these nanocomposites for specific applications.