Microwave-Assisted Fabrication and Characterization of Carbon Fiber-Sodium Bismuth Titanate Composites

Abstract

Lead-based piezoelectric materials cause many environmental problems, regardless of their exceptional performance. To overcome this issue, a lead-free piezoelectric composite material was developed by incorporating different percentages of carbon fiber (CF) into the ceramic matrix of Bismuth Sodium Titanate (BNT) by employing the microwave sintering technique. The aim of this study was also to evaluate the impact of microwave sintering on the microstructure and the electrical behavior of the carbon-fiber-reinforced Bi_0.5Na_0.5TiO₃ composite (BNT-CF). A uniform distribution of the CF and increased densification of the BNT-CF was achieved, leading to improved piezoelectric properties. X-ray diffraction (XRD) showed the formation of a phase-pure crystalline perovskite structure consisting of CF and BNT. A Field Emission Scanning electron microscope (FESEM) revealed that utilizing microwave sintering at lower temperatures and shorter dwell times results in a superior densification of the BNT-CF. Raman Spectroscopy confirmed the perovskite structure of the BNT-CF and the presence of a Morphotropic Phase Boundary (MPB). An analysis of nanohardness indicated that the hardness of the BNT-CF increases with the increasing amount of CF. It is also revealed that the electrical conductivity of the BNT-CF at a low frequency is significantly influenced by the amount of CF and the temperature. Moreover, an increase in the carbon fiber concentration resulted in a decrease in dielectric properties. Finally, a lead-free piezoelectric BNT-CF showing dense and uniform microstructure was developed by the microwave sintering process. The promising properties of the BNT-CF make it attractive for many industrial applications.

1. Introduction

Piezoelectric materials are widely employed in various applications, e.g., transducers, actuators, and sensors, due to their superior qualities. The Lead Zirconate Titanate (PZT) system is the most common material among the available alternatives, as PZT ceramics showcase remarkable piezoelectric attributes. However, the production of PbO₂ vapors during the firing procedure has rendered PZT-based ceramics ecologically hazardous. Hence, it is critical to explore lead-free piezoelectric ceramics, which minimize the environmental harm associated with PZT and provide higher performance capabilities [1,2]. Many of the families of BNT [3,4], Potassium Sodium Titanate (KNN) [5,6,7], and Barium Zirconate Titanate (BZT) [8,9] were discovered to be substitutes for lead-based piezoelectric materials, having a promising high curie temperature (Tc > 320 °C), a comparatively substantial remnant polarization, and a large coercive field [10]. Among these, BNT is an optimal solution because of its high curie temperature, microstructure stability at elevated temperatures, and better electrical properties at higher frequencies.

Researchers found that doping or adding other elements to create solid solutions could considerably increase the overall characteristics of BNT ceramics. BNT-based materials’ properties have been enhanced by combining them with some other elements like Bi_0.5Na_0.5TiO₃-BaTiO₃ (BNT-BT) [11,12] and Bi_0.5Na_0.5TiO₃-Bi_0.5K_0.5TiO₃ (BNT-BKT) [13,14,15,16] to facilitate their use in sensors and actuators. Ion doping and composite fabrication methods can significantly enhance the charge–discharge performance and energy storage properties of BNT materials [17]. The presence of a Morphotropic Phase Boundary (MPB) contributes to the promising characteristics of other BNT systems [18].

The synthesis of BNT is comparatively easy as compared to KNN and Bismuth Titanate (BT) ceramics. The strong conductivity and high coercive field of undoped BNT ceramics make poling treatment challenging. A study by Nagata et al. indicated that the pinning of the domain walls formed by oxygen vacancies due to bismuth vaporization at high sintering temperatures is the root of the difficulty in poling BNT. This research also concluded that weight loss begins at approximately 1130 °C in BNT ceramics [19]. The high temperature requirements for the sintering and calcination of Bi₂O₃ and Na₂CO₃ causes volatility issues in these compositions. However, both materials have low melting points (Bi₂O₃ T_m = 826 °C, Na₂CO₃ T_m = 851 °C), and high vapor pressure at operating temperatures results in the loss of A-site cations, which results in non-stoichiometric composition and causes vacancies. The volatilization of materials or the formation of secondary phases occurs to regain the stoichiometry [20,21]. Low sintering temperatures and the improved densification of ceramics can be accomplished to improve the characteristics of BNT ceramics. Moreover, to maintain stoichiometry, a low sintering temperature is required [22]. Energy density and electric breakdown strength have been increased using a special microwave sintering technique. Combining cold isostatic pressing with microwave sintering results in a green body that is denser and isotropic, which produces a homogeneous heat from all directions at a rapid heat rate. This can lower the formation of all byproducts and encourage mass transfer and diffusion [23].

The microwave sintering process enables low-temperature sintering with a reduced dwell time and directly applies heat to the samples while the heating profile is applied from the interior to the exterior. The process entails volumetric heating, so it is a fast process, and the densification is achieved while avoiding any accompanying grain growth [24]. Hence, the use of microwave sintering has proven critical in increasing the sintering rate, decreasing the sintering cycle, lowering the sintering temperature, and subsequently creating high-density ceramics [25,26]. This particular methodology has resulted in a high degree of uniformity coupled with a considerable increase in densification that has the potential to enhance the electrical and mechanical characteristics of ceramics [27].

Microscale two-phase composite fabrication can be used to enhance the electric breakdown (E_B) of BNT ceramics, as it is widely known that ceramics can easily break through the grain boundary. Previously, research has been conducted by adding insulating metallic oxides such as MgO [28,29], ZnO [30], and SiO₂ [31] that caused precipitation on the grain boundary, which increased the breakdown strength. A small amount diffuses inside the grain, while the excess precipitates near the grain boundary, hindering grain growth and causing its size to be reduced. The graphene and carbon nanotube incorporation improves the properties of ceramic nanocomposites [28,29]. Previous studies indicate that grain size reduction enhances ceramic materials’ E_B [30]. Tunkasiri et al. established the correlation between E_B and the grain size (G) of the ceramics. $E_B\propto {\displaystyle \frac{1}{\sqrt{G}}}$ illustrates that the reduction in the size can improve the E_B [31]. Carbon fibers were incorporated in this study, and their effect on the ceramic structure and properties was examined. Carbon fiber is the most promising form of fiber because of its exceptional strength and low weight, which remain consistent up to a temperature of 2000 °C in an inert atmosphere and in a vacuum [29]. Carbon fiber composites present good temperature storage performance as well as highly responsive heating [32]. At the same time, dense nanocomposites can be produced by using the microwave sintering process, and it can inhibit the carbon nanotube (CNT) damage that is associated with hot pressing [33]. With its rapid and localized heating, microwave sintering can help to preserve the structural and mechanical properties of the carbon fibers by minimizing prolonged exposure to high temperatures. This technique was performed in a controlled atmosphere, which helps in managing oxidation or other chemical reactions that might affect the carbon fibers. Therefore, microwave-sintered carbon fibers are also expected to have a promising impact on the properties of BNT ceramics.

2. Materials and Method

2.1. BNT Powder Preparation

BNT ceramics in pure form were synthesized using the standard method of solid-state reaction, which is a simple and economical method. Reagent-grade oxides of Na₂CO₃ (99.95%, Sigma Aldrich®, St. Louis, MO, USA), Bi₂O₃ (Sigma Aldrich® 99.9%), and TiO₂ (Sigma Aldrich® 99.9%) were used as raw materials and weighed based on the stoichiometric calculation, i.e., Bi_0.5Na_0.5TiO₃. The powder was dried at 200 °C for one hour before mixing to remove any moisture content. Then, a wet ball-milling process was used, where the mixture of powder was ball-milled in ethanol having a ball-to-powder ratio (BPR) of 20:1, and the ethanol-to-powder ratio was set at 5:1 for 4 h using ZrO₂ balls with a ball-milling speed of 400 RPM. After the ball milling, the mixture was put into a jar where the balls were carefully removed by washing them with acetone in a syringe so that no powder would be stuck on the ZrO₂ balls. After that, the jar, which contained the BNT powder, was kept in the oven for drying, and dried powder was obtained. Furthermore, the powder was calcined in a box furnace for 2 h at 850 °C at a heating rate of 10 °C/min, followed by cooling of the furnace. The calcined powder with the same parameters was ball-milled.

2.2. BNT-Carbon Fiber Composite

The carbon fibers (CFs) were initially chopped and sieved through two mesh-size sieves. They were thoroughly cleansed in an ultrasonic cleaner using ethanol. The resulting carbon fiber sizes obtained were approximately 60–70 µm. These fibers were mixed with BNT at different weight percentages by a vacuum mixer at a speed of 2000 RPM for 2 min with an interval of 30 secs for each composition. The final powder product had a composition of BNT with varying percentages of 0 wt.%, 0.5 wt.%, 1 wt.%, 2 wt.%, and 5 wt.% of carbon fibers. To create cylindrical pellets, the blended powder was mixed (~1.0 g) and then cold-compressed at 80 MPa for 90 s. The green pellets were 13 mm in diameter and 3 mm thick.

The microwave sintering was performed at 1000 °C with a 10 °C/min heating rate and held for 20 min at the peak temperature. Bi₂O₃ powder was sprinkled next to the green pellet to minimize bismuth loss during sintering to preserve the bismuth-rich environment. The oxides (Bi₂O₃) are more stable and can act as a buffer to reduce the vaporization of Bi during the sintering process. Furthermore, the spreading helps to maintain the stoichiometric balance of Bi in the BNT system. The sintered ceramic composites were gradually cooled in a furnace to prevent any quenching effects [34]. The density of composites was calculated using Archimedes’s Principle and found to be ~95%. Figure 1 schematically presents the steps involved in the synthesis of the carbon-fiber-reinforced Bi_0.5Na_0.5TiO₃ composite (BNT-CF).

2.3. Characterization

The purity of BNT-CF was identified using an X-ray diffractometer (Rigaku. Miniflex 2 Desktop, Tokyo, Japan). The X-ray pattern was recorded within a range of 2θ = 20–80° at 45 kV and 40 mA using copper anode radiation with a 1.5°/min scanning rate and 0.02° step size. For the study of microstructure, polished sintered samples were examined by a Field Emission Scanning Electron Microscope (FESEM) using FE-SEM-Nova Nano-450, Breda, Netherlands. The surface morphology was studied by an Atomic Force Microscope (AFM) using an MFP-3D Asylum research (Santa Barbara, CA, USA) device equipped with a silicon probe (Al reflex coated Veeco model OLTESPA, Olympus, Tokyo, Japan) in contact mode. Raman Spectroscopy was carried out using Raman Thermo Scientific DXR3 Waltham, MA, USA. The mechanical properties of the sample were evaluated by attaching the MFP-3D nanoindenter to the AFM by using a Berkovich diamond indenter tip with the highest 1.00 mN indentation force. The values of nanoindentation were calculated from loading–unloading curves. The electric properties were calculated by a Precision LCR meter (Tonghui TH2829C, Bologna, Italy) with a range of 20 Hz–1 MHz.

3. Results and Discussions

3.1. X-ray Diffraction

Figure 2 illustrates the X-ray diffraction analysis of the sintered BNT. In the sintered BNT, the crystalline phases were identified and indexed properly from the powder diffraction card (PDF) by JCPDS Card No: 36-0340. Usually, ABO₃ perovskite shows diffraction peaks at (32°, 46°, and 58°).

It is evident that all the BNT samples are made of a single phase and clearly show typical ABO₃ perovskite diffraction peaks at room temperature [35,36]. Moreover, the XRD pattern shows the existence of defined and sharp diffraction peaks, indicating the formation of well-defined and targeted sintered compositions. Figure 2a shows the XRD pattern of the microwave-sintered BNT-CF having varying compositions of carbon fiber (0.5%, 1%, 2%, and 5%). It is persistent that no additional phases were observed for the BNT ceramics when various amounts of carbon fiber were incorporated. This indicates that the carbon fiber has been dispersed properly into the BNT structure to produce a homogenous composite structure for all compositions [36]. Furthermore, the characteristic carbon peak appears at an angle of 43°, indicating the presence of carbon fiber in the BNT. The tetragonal structure exhibits a splitting of the (200) peak that was utilized to determine the presence of the Morphotropic Phase Boundary (MPB); the split peaks at 46–47° imply that a rhombohedral–tetragonal phase transition occurs, which can be noticeably seen in Figure 2b [36,37,38]. High piezoelectric properties are usually obtained from a stable MPB structure [39,40].

3.2. Scanning Electron Microscopy

Figure 3 displays the particle-size analysis of the BNT powder obtained after ball milling, which shows that the BNT powder has an average particle size of around 500 nm. Moreover, in Figure 4, the FE-SEM results revealed that all the BNT-CF samples were effectively dense and with fully developed rectangular grain shapes, which is typically observed in the microstructure of BNT piezoceramics. It can be noticed that a clear, round equiaxed grain and uniform grain size, without any cluster formation of carbon fibers, prevails in the BNT-CF samples. The carbon fiber is well integrated within the BNT structure while maintaining its individual existence with phase boundaries. Moreover, a comparison of the surface morphology of the BNT and BNT-CF with the carbon fiber composition ranging from x = 0 to 5 is also presented in Figure 4, showing the presence of a dense and compact structure. The grain sizes from the given micrographs were measured using ImageJ software (Version 1.54j), as shown in Figure 5. For the bare BNT, the average grain size is around 2.4 µm, and for the compositions x = 0.5, x = 1, x = 2, and x = 5, the average grain size decreases to 1.5 µm, 0.64 µm, 0.57 µm, and 0.56 µm.

It can be observed that by increasing the carbon fiber content in the BNT-CF, the grain size decreases. The restricted behavior of carbon fibers towards the grains makes it possible to reduce the grain size. This suggests that non-metallic CFs hindered the grain growth in the BNT. Furthermore, the grain growth rate (G) and nucleation (N) are the fundamental factors influencing grain growth. The grain growth rate and nucleation have opposing effects; a small ratio of N to G will result in a high final grain size, while a large ratio of N to G will result in a small final grain size. Therefore, the enhanced nucleation rate induced by the increased nucleation sites created by carbon fibers is mostly responsible for the reduction in grain size. Additionally, the CFs served as pinning points, which probably inhibited grain development at high temperatures [41].

In the microwave-sintered samples, the rapid heating rate of the microwaves prevented undesirable grain growth and provided more fine and uniformly distributed grains, which is considered to be an attractive feature for the processing of piezoelectric materials [42]. Incorporating a dense and uniform microstructure in the materials can greatly enhance their properties. The above discussion reveals that all the sintered BNT-CF samples demonstrate dense structure with minimum porosity.

An EDX analysis of the BNT and BNT-2CF was conducted to determine the sample’s elemental composition. The results are presented in Figure 6, which shows the peaks of Bi, Ti, Na, and O. In contrast, a new peak of carbon emerged in Figure 6b, which confirms the successful incorporation of the carbon into the BNT structure.

3.3. Raman Spectroscopy

In ceramics, the phase transition that occurs due to perovskite distortion can be detected by Raman Spectroscopy [43]. Moreover, this technique was deployed to detect the existence of the Morphotropic Phase Boundary (MPB). Figure 7 displays the Raman spectra for the BNT-CF containing different concentrations of CF from 100 to 1000 cm⁻¹, showing six broad Raman peaks positioned at 137, 279, 529, 580, 758, and 834 cm⁻¹, which is consistent with the already published results [44,45]. The width of the Raman spectra peak shows disorder on the A-site and overlapping of peaks. The peak appears at a lower Raman shift of 137 cm⁻¹ labeled as peak A, showing vibrations of cations on the A-site in the ABO₃ perovskite structure [46]. Peaks that appeared between 100 and 200 cm⁻¹ correspond to the confirmed vibration bands of Bi-O and Na-O bonds, and the peak that appeared around 137 cm⁻¹ is associated with the Na-O bond vibrations [47]. Wang et. al. reported that the band indicates the presence of local Na⁺TiO₃ groups of multiple unit cells. Also, Bi-O bonds are not expected in this section, as Bi-O bonds must occur at <100 cm⁻¹ because of the large Bi mass [37]. The Raman data demonstrate no substantial deviations in the Raman shift or magnitude of peak A with rising carbon fiber contents.

Peak B, centered at 280 cm⁻¹, is consigned to Ti-O vibrations [48], whereas peaks C and D at ~529 cm⁻¹ and 580 cm⁻¹ are due to vibrations of TiO₆ octahedra [49,50]. Broad peaks emerged from the overlapping of peaks, and disorder of the A-site happened due to the presence of various Bi³⁺ and Na⁺ ions [51]. The Raman spectra show that the centered peak B position at ~280 cm⁻¹ slightly moves towards the higher Raman shift with the increasing addition of carbon fiber. This shift may be due to the structural disorder as well as the existence of oxygen vacancies in the system [49].

The modes that exist between the range of 450 and 650 cm⁻¹ are changed after the addition of the CF. The splitting of the peak in region C indicates the presence of a mixed rhombohedral and tetragonal crystal structure that confirms the MPB nature [52]. The spectra at 529 cm⁻¹ and 580 cm⁻¹ are responsive to the deviations in structure from rhombohedral to tetragonal, according to the findings of research on another perovskite type of ceramics [50]. The splitting of these peaks becomes more prominent when the concentration of CF increases. These BNT-CFs at the aimed compositions exhibit an MPB nature, further supporting the XRD data (Figure 2). It is reported that a multi-structure in a solid solution improves dielectric and ferroelectric properties [53,54]. Apart from broadening and weakening in the frequency band between 700 and 900cm-1, no significant changes in composition are noticed for peaks E and F of the BNT. These bands are observed due to the shifting of O [55].

3.4. Atomic Force Microscopy

Figure 8 shows the surface topography of the BNT-CF containing different amounts of CF. The surface roughness of the BNT-CF increases with the increasing concentration of CF. The surface roughness value was analyzed by comparing the Root Mean Square (RMS) roughness parameter for the BNT and BNT-CF. The RMS value measured for the bare BNT is 42.840 nm, which presents a smooth surface. However, it is observed that the surface roughness of the BNT-CF increased due to the addition of carbon fiber, and a maximum value of 105.264 nm is achieved for the BNT-5CF.

3.5. Nanohardness

Figure 9 shows the nanohardness value for the BNT and BNT-CF with different concentrations of CF. It can be seen that the nanohardness gradually increases with the increasing content of CF. This increase may be due to the possibility of a dispersion hardening effect due to the presence of hard fibers [56]. Moreover, grain refinement also has a hardening effect because of the presence of CFs within the matrix [41]. Although the increase in CF concentration in the BNT structure helped to increase the hardness of the material, there is a significant drop in the BNT-5CF sample. This suggests that incorporating a high amount of carbon fibers may lead to a mismatch of reinforcing fibers and ceramic matrix, which results in stress concentrations, reduced load-bearing capacity, and, ultimately, lower nanohardness. This is also evident from the Atomic Force Microscopy, where the RMS value for the BNT-5CFs is greater than other compositions. The higher CF concentration significantly impacts the carbon fibers’ alignment within the ceramic matrix. If the fibers are not aligned properly or there is poor interfacial bonding between the ceramic and the fibers, nanohardness can be reduced.

3.6. Conductivity Study

3.6.1. Effect of Frequency on Conductivity

The study of AC conductivity is valuable for gaining a better understanding of the compound’s electrical conductivity by examining its frequency dependency. The fluctuation in AC conductivity with frequency provides information about the behavior of charge carriers (electrons and holes).

To understand the basic feature, a plot is created between the AC conductivity (σ_ac) and frequency at various temperatures. The conductivity value is acquired from the R by the relation

$${\mathsf{\sigma }}_{\mathrm{ac}}={\displaystyle \frac{\mathcal{l}}{AR}}$$

(1)

where ℓ is thickness and A is the effective area of the material. The fluctuation in AC conductivity of the BNT-CF containing various concentrations of CF as a function of the frequency at various temperatures (50–500 °C) is presented in Figure 10.

For BNT, the conductivity is independent of frequency within this frequency range, so no change in conductivity is observed, even at a frequency value of 1 M Hz. The conductivity of BNT-CF increases at a frequency of 600 KHz by increasing the carbon fiber, and a further increase in carbon fiber results in a shift in the rise in conductivity at low frequency and elevated temperatures. For the BNT-5CF, an increase in conductivity occurs at 200 KHz. The region has little to no effect on frequency at lower temperatures, and then it smoothly relaxes to a strong dispersive region. A further increase in temperature causes broad dispersion in conductivity. At higher temperatures (400–500 °C), the conductivity curves narrow down and seem to merge. However, they did not merge completely. This phenomenon of merging the curves is due to the release of space charges [57].

Moreover, with the increase in temperature and frequency, the conductive ion returns to its original location due to less time and random collisions, making it a failed hop, resulting in failure. As a result, the ratio between successful and unsuccessful hops causes dispersion in conductivity at high frequencies and temperatures. Moreover, the structure transition occurs, providing unoccupied sites with more mobile ions at elevated temperatures. Increased AC conductivity with rising temperature indicates a Negative Temperature Coefficient of Resistance behavior (NTCR). The fluctuation in AC conductivity with temperature spikes after 300 °C. The data reported herein indicate the thermal activation of the conduction mechanism.

There is no significant increase in conductivity at the low-frequency regions for all temperature ranges. Conductivity curves at low frequencies give DC conductivity. The relaxation jump hypothesis helps to explain the observed frequency-independent σ_dc. Conduction occurs at low frequencies and high temperatures as charged particles bounce from one localized state to another. This leads to a wide range of translational motion of charge carriers, which increases σ_dc [58].

3.6.2. Activation Energy

Activation energies are calculated using the Arrhenius equation, as expressed below, to characterize the conduction mechanism at various frequencies.

This equation is τ = τ_o exp (E_a/k_BT), where τ_o is the pre-exponential factor, E_a shows the activation energy for charge transfer, k_B represents the Boltzmann constant (1.3807 × 10⁻²³ J K⁻¹), and T stands for the absolute temperature.

Table 1. Activation energy for sintered composite samples at 1 MHz.

SR. Number	Sample	Ea
1.	BNT	0.34
2.	BNT-0.5CF	0.15
3.	BNT-1CF	0.1
4.	BNT-2CF	0.03
5.	BNT-5CF	0.33

shows the calculated activation energies of the sintered BNT-CF containing different concentrations of CF at various frequencies. The values of activation energy appeared to decrease at a high frequency value (1 MHz).

Figure 11 clearly shows that the value of the activation energy decreases with the addition of CF into the BNT-CF. This is due to the fact that carbon fibers are inherently electrically conductive because of the delocalized π-electrons in their structure. When carbon fibers are added to ceramic materials like BNT, they create pathways for the conduction of electrons, which causes a decrease in activation energy.

Carbon fibers can facilitate the movement of charged defects by providing pathways for electron conduction. This can enhance the mobility of ions or vacancies within the ceramic matrix. In ceramic materials, electrical conductivity can influence the migration of charged defects (such as ions or vacancies). It is observed that activation energy tends to drop up to a certain point, and a 5% addition of carbon fiber increased it again. Although the addition of CF in small amount can lower the activation energy by enhancing conductivity and facilitating charge transport, further additions beyond an optimal threshold can lead to detrimental effects such as overcrowding or the disruption of pathways critical for ion movement. These effects can ultimately result in an increase in activation energy, potentially returning it to levels similar to those observed in the absence of carbon fibers. The acquired results indicate that conduction is caused by a thermally stimulated process.

3.6.3. Dielectric Properties

The dielectric behavior strongly depends upon temperature and frequency [59,60]. Figure 12 illustrates the dielectric behavior of the BNT-CF containing different amounts of CF with respect to temperature at various frequencies. Two dielectric humps are observed in these graphs. The first anomaly is observed between room temperature and 180 °C, which can be termed the depolarization temperature (Td) [61], and the second is detected at temperatures above 320 °C. Where the dielectric constant value is maximum, that temperature is the maximum permittivity temperature (T_m) [47,62]. This shows that the increase in CF concentration has caused a decrease in dielectric properties at the frequency of 1 MHz. An increase in the carbon fiber content also increases the dielectric loss (Tanδ). It is illustrated in the graphs that tanδ rises with a temperature rise. The increase in tanδ is more significant at higher temperatures because of the high electrical conductivity. The movement of electric dipoles becomes maximum at high temperatures. At first, the dielectric loss is triggered by the interfacial properties of the composites; after that, the increase in carbon fibers causes a huge amount of heat generation during the polarization process, contributing to the dielectric loss. After a 2% addition of CF, the dielectric constant is half of its initial value because the excessive amount of fiber causes some escalation of the internal pores. Moreover, adding more CF content decreases the dielectric constant, and dielectric loss (tan δ) increases, signifying that the established percolation network is not steady and can be easily damaged by external frequency disturbances. The adjustment between the high values of the dielectric constant coupled with a low dielectric loss of compounds makes them ideal for various device applications.

4. Conclusions

A lead-free piezoelectric composite material (BNT-CF) was developed by reinforcing the Bi_0.5Na_0.5TiO₃ (BNT) matrix with varying concentrations of carbon fiber (CF) by employing the microwave sintering technique. A structural analysis confirmed the formation of a phase-pure crystalline perovskite structure with a stable Morphotropic Phase Boundary (MPB). Microwave sintering of the BNT-CF at a low temperature and shorter dwell time results in superior densification and a more uniform microstructure with minimum porosity. The conductivity of the BNT-CF is influenced by the concentration of the CF, temperature, and frequency. The improvement in the electrical conductivity of the BNT-CF with increasing amounts of CF can be ascribed to the inherent high electrical conductivity of CF, which facilitates the movement of charged defects by providing pathways for electron conduction. Moreover, the dielectric properties of the BNT-CF are sensitive to the amount of CF; a gradual increase in the dielectric loss (Tanδ) and a decrease in the dielectric constant (ε) is noticed with the increase in CF. As a comparison, the BNT-CF with 2% carbon fiber exhibits optimal structural, mechanical, and dielectric properties.