Morphotropic Phase Boundary Region 0.7BiFeO₃-0.3BaTiO₃ Ceramics Exploration Under the Influence of the Incorporated Sn-Ions for Piezo/Ferro Applications

Abstract

In the field of piezoelectric applications, perovskite-based multifunctional composite ceramics are widely explored. The morphotropic phase boundary (MPB) regions, where dual structural phases coexist, play a crucial role in boosting the ferroelectric and piezoelectric properties significantly. Herein, MPB-region-existent 0.7BiFeO₃-0.3BaTiO₃ (BFBT) composite ceramic is investigated under the influence of wt%Sn-ion incorporation at the lattice sites of the BFBT. Specifically, the ceramic composition BFBT:0.2Sn has demonstrated excellent remnant polarization (P_r ~ 22.68 µC/cm²), an impressive piezoelectric coefficient (d₃₃ ~ 211 pC/N), stable impedance of 1.07 × 10⁷ Ω, a Curie temperature of 435 °C and low dielectric loss (tanδ) of <0.5. Moreover, the BFBT:0.2Sn ceramic has also maintained a stable d₃₃ of ~150 pC/N and resistivity of ~10² Ω even at a temperature of 400 °C. Such outcomes confirm the ability and potential of the BFBT:0.2Sn ceramic composition for high-temperature piezoelectric applications.

1. Introduction

The future-oriented smart electronic industry demands materials capable of operating in two highly energetic structural phases. Such dual structural existence in the form of a morphotropic phase boundary (MPB) within a single material holds the potential to significantly enhance both piezoelectric and ferroelectric properties to elevate the performance of devices [1,2,3]. Such MPB-existent composite materials also establish the field-driven reversible phase transformation that is vital for high-temperature piezoelectric devices [4]. Lots of reports are available regarding the lead-based and lead-free ceramics that possess MPB regions, highlighting the field-driven reversible phase transformation that can be initiated by an applied electric field [5,6,7]. Owing to the toxic behavior of lead-based perovskite ceramic materials, the focus of researchers has shifted toward exploration of lead-free perovskite materials, which must be capable of simultaneously demonstrating strong multifunctional properties [8].

Among the various types of perovskite materials, BiFeO₃ possesses significant importance, as it contains a rhombohedral structure with the space group R3c and a high Curie temperature of ~820 °C. Moreover, it possesses the ability to exhibit magnetoelectric properties simultaneously at room temperature [9]. BiFeO₃ has been widely explored to establish the MPB regions with other counterparts, including SrTiO₃ [10], Na_0.5K_0.5NbO₃ [11], BaTiO₃ [10], and Bi_0.5Na_0.5TiO₃ [12]. Another important member of the perovskite family is BaTiO₃, which contains a tetragonal structure with the space group P4mm [13]. The combination of BiFeO₃ (rhombohedral, R) with BaTiO₃ (tetragonal, T) results in the establishment of an R-T-based MPB region in the composition 0.7BiFeO₃-0.3BaTiO₃ [14]. However, there is ongoing debate in the literature regarding the exact nature of the phases in this MPB region. Some studies suggest the coexistence of rhombohedral and pseudo-cubic phases rather than a clear R-T transition. Moreover, the research on the 0.7BF-0.3BT composition has reported different piezoelectric coefficients (d₃₃), ranging from 134 to 191 pC/N [15,16]. Recently, Qin et al. have reported the maximum polarization (P_max) of 27.3 µC/cm² for the ceramic composition 0.66BF-0.34BT [17]. Habib et al. investigated the Bi³⁺-site with La-substitution effects and revealed a chemical-induced structural phase transition and a large static piezoelectric constant (d₃₃ = 274 pC/N) with a high Curie temperature (T_C = 532 °C) [18]. Lee et al. reported a water-quenching process, which increased the d₃₃ and T_C to 240 pC/N and 456 °C, respectively [19]. Habib et al. achieved a high T_C of 450 °C and an outstanding d₃₃ of 422–436 pC/N by substituting Ba²⁺ with Yb³⁺, Y³⁺, Sm³⁺, and Nd³⁺ [20]. Lee et al. introduced a rapid ceramic powder synthesis and low sintering temperatures with a quenching process, which improved the piezoelectric properties [21]. Cheng et al. reported significantly enhanced insulating and piezoelectric properties by fine-tuning the calcination temperature of 0.7BiFeO₃-0.3BaTiO₃ [22]. Many researchers have tried to improve the ferroelectric and piezoelectric performances of the material by doping/adding elements/materials at the specific reported MPB region, but the regular development of non-perovskite secondary phases like Bi₃₆Fe₂O₅₇, Bi₂₅FeO₃₉, or Bi₂Fe₄O₉ during the cooling process required for fabrication continued to occur, while the volatile nature of Bi₂O₃ for BiFeO₃ is still a big hurdle to the development of this composition [2].

Among the transition metal oxides (TMOs), SnO₂ has significance importance due to its n-type semiconductor nature with a wide band gap of ~3.6 eV, meaning it performs best in sensor applications [23]. SnO₂ possesses a crystal structure similar to the tetragonal rutile with the space group P4₂/mnm [24]. Jankowska-Sumara et al. specified that the low content incorporation of Sn⁴⁺ in the PbZrO₃ ceramic host matrix possesses the ability to reduce the strong occurrence of a new ferroelectric transient phase before reaching the Curie temperature (T_C) and reinforce the first-order character phase transition [25]. Wang et al. reported the improvement of the ferroelectric and piezoelectric performances of the Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ ceramic system with the incorporation of SnO₂ [26]. Hence, SnO₂ possesses the ability to easily incorporate into the lattice space of the host materials to occupy the available vacancy and improve the multifunctional properties of the materials.

In this article, an MPB-region-existent 0.7BiFeO₃-0.3BaTiO₃ (BFBT) composite with wt%SnO₂ addition is engineered and investigated as the formula 0.7BiFeO₃-0.3BaTiO₃: wt%SnO₂ with wt% = 0–0.25 (BFBT:wt%Sn). It is observed that the BFBT:0.2Sn composition ceramic displays excellent ferroelectric behavior (P_r ~ 22.68 µC/cm²) and an impressive piezoelectric coefficient (d₃₃ = 211 pC/N). Moreover, the BFBT:0.2Sn ceramic maintains a d₃₃ of 150 pC/N even at a temperature of 400 °C, confirming the potential of the material to be utilized in high-temperature piezoelectric applications.

2. Experimental and Characterization

The MPB-region-existent 0.7BiFeO₃-0.3BaTiO₃ composition has been fabricated using the solid-state reaction method. High-purity chemicals, Bi₂O₃ (99.99%, Sigma Aldrich, St. Louis, MO, USA), Fe₂O₃ (99.9%, Sigma Aldrich), BaCO₃ (99.99%, Aladin, Nanjing, Jiangsu, China) and TiO₂ (99.9%, Sigma Aldrich, St. Louis, MO, USA), have been unitized using the stoichiometric ratio of BFBT. The powders were mixed in ethanol, milled for 15 h, dried at 150 °C overnight and later calcined at 850 °C for 2 h. The calcined BFBT powder was mixed with SnO₂ (99.9%, Sigma Aldrich, St. Louis, MO, USA) at varying weight percentages of 0.0 to 0.25 (i.e., wt% = 0, 0.1, 0.15, 0.2, and 0.25). The mixture was ground to a precise diameter, milled at same rate for 10 h, dried at 150 °C overnight and pelletized into disk shapes with a diameter of 11 mm under 150 MPa hydrostatic pressure. Finally, the pressed pellets were placed in a sealed crucible with an extra amount of BFBT powder around the disks to avoid the evaporation process during the high-temperature sintering process and sintered at 1010 °C for 4 h with a rapid increase/decrease of 30 °C/50 °C in temperature per minute to avoid the evaporation of Bi.

X-ray diffraction was performed to analyze the crystallinity, structure and phase purity of the ceramics using a PANalytical device (Almelo, The Netherlands). The crystallite size (D) of the pure and Sn-modified 0.7BiFeO₃-0.3BaTiO₃ was estimated using Scherrer’s equation (Equation (1)):

$$D={\displaystyle \raisebox{1ex}{$K\lambda $}\!\left/ \!\raisebox{-1ex}{$\beta Cos\theta $}\right.}$$

(1)

where λ is the wavelength of the X-ray, β is the full width of the peak at half maximum in radians, θ is the diffraction angle, and K is the Scherrer’s constant. The dislocation density (q) and lattice strain (e) for all the samples were calculated using the following equations:

$$Dislocation Density \left(q\right)={\displaystyle \raisebox{1ex}{$15\in $}\!\left/ \!\raisebox{-1ex}{$aD$}\right.}$$

(2)

where a is the lattice constant and D is the crystallite size estimated from Scherrer’s formula.

$$Lattice Strain \left(e\right)={\displaystyle \raisebox{1ex}{$\beta $}\!\left/ \!\raisebox{-1ex}{$4\tan \theta $}\right.}$$

(3)

The morphological variation in the ceramic compositions was observed by scanning electron microscopy (SEM, FEI Quanta 200, Hillsboro, OR, USA). Later, ceramic samples of all the compositions were polished to a thickness of 0.7 mm and Ag electrodes were pasted on both surfaces of the ceramics for the measurement of the ferroelectric, piezoelectric, electric and dielectric properties. The ferroelectric tester produced by Radiant Technologies (Albuquerque, NM, USA) was utilized for measuring the polarization versus the electric field loops (P-E loops) at a varying electric field range of 0–80 kV/cm at 10 Hz. The piezoelectric performances of all the ceramic compositions were measured by a piezo-d₃₃ meter (model IAAS ZJ-30 Institute of Acoustics of CAS, Beijing, China) at 60 Hz. Firstly, the ceramics were poled at 90 kV/cm (100 °C), and later, the piezoelectric coefficient (d₃₃) was measured at room temperature. Later, the poled ceramic samples of all the compositions were annealed for the temperature range of 50–600 °C, with a step size of 50 °C for 30 min, and their d₃₃ was measured at room temperature to analyze the piezoelectric stability with the temperature variation. An Agilent 4294A produced by Hewlett-Packard Co., Palo Alto, CA, USA, was employed for measuring the impedance versus the frequency plot of all the ceramic compositions. A Keithley 2611 was used for measuring the resistivity versus the temperature (range: 25–500 °C) plot of all the ceramic compositions; the device was attached to the temperature-controllable furnace and computer. For the measurement of the Curie temperature (T_C) and the ceramic samples’ stability in terms of the properties, the dielectric constant (ε_r) versus temperature plots and the dielectric loss versus temperature (15–600 °C) at varying frequencies of 100 Hz to 1 MHz were measured by an LCR analyzer model HP4980A (Agilent, Santa Clara, CA, USA).

3. Results and Discussion

The XRD analysis of the BFBT:wt%Sn (wt% = 0–0.25) ceramic samples for 2θ = 20–65° is presented in Figure 1a. All the ceramics have maintained their perovskite structure and no phase impurity or secondary phase has been detected in the patterns, confirming that the Sn-ions have been successfully incorporated into the lattice sites of the BFBT host to occupy the vacancies and caused no destruction of the structure. Sn⁴⁺ ions possess a smaller ionic size compared to Bi³⁺; however, their charge facilitates compensation for vacancies located at both the A-site and B-site positions. Given that Sn⁴⁺ possesses an ionic radius comparable to that of Fe³⁺ (0.645 Å) and Ti⁴⁺ (0.605 Å), it is more possible that Sn is substituting for Fe or Ti within the B-site rather than for Bi³⁺ at the A-site. This substitution mechanism aids in preserving the charge neutrality and compensates for the reduction of volatile Bi that occurs during the sintering process. The XRD patterns are indexed by comparison with the standard PDF # 71-2494 of BiFeO₃ [27] and PDF # 76-0744 of BaTiO₃ [28]. An enlarged image of the XRD analysis for 2θ = 36–48° is presented in Figure 1b, where the MPB region is confirmed by the presence of a shoulder-like peak in the asymmetric (200) plane, showing the rhombohedral R (space group R3c from BiFeO₃) and tetragonal T (space-group P4mm from BaTiO₃) phases, which is consistent with previous studies [2,16]. The addition of Sn-ions into the lattice sites of the BFBT host has made this duality of structure more prominent. This prominence of the peak in the (200) plane indicates that the tetragonal phase of the MPB region is dominating with the increase in the Sn-ions content. But throughout the scheme of the XRD patterns, the MPB region has maintained its identity. For an in-depth study of the crystallographic information, refinement of the XRD patterns was performed for all the compositions using the rhombohedral (R, R3c) and tetragonal (T, P4mm) phases as reference structures. The X-ray diffraction (XRD) refinement analysis is illustrated in Figure 1c–f, elucidating the simultaneous existence of rhombohedral (R3c) and tetragonal (P4mm) phases within the BFBT:wt%Sn ceramics. The diffraction peaks associated with the rhombohedral phase (R) and tetragonal phase (T) are distinctly identified, particularly at significant diffraction angles that align with these crystalline structures. In all the analyzed samples in Figure 1c–f, both R and T phases are concurrently fitted, signifying the presence of a phase mixture. The continuous presence of both tetragonal (depicted by green lines) and rhombohedral (represented by pink lines) peaks throughout the entire compositional spectrum (from undoped BFBT ceramic to 0.25 Sn-added ceramic) indicates the coexistence of these two phases. The refinement statistics, including the χ², R_wp, and R_p, exhibit reasonable values, suggesting a satisfactory fit for both the R and T phases. The XRD refinement data of the BFBT:0.1Sn ceramic are presented in Supplementary Information (SI) Figure S1. Nonetheless, the lack of a pronounced separation or additional peak broadening at lower angles, particularly adjacent to the (111) reflection, implies that while the R phase is present, it does not predominate in the structural framework. This absence of evident peak splitting may signify a refined rhombohedral distortion. The coexistence of these two phases, as delineated in the XRD data, reinforces the assertion that the system is situated within the morphotropic phase boundary (MPB) region. The MPB is characterized by enhanced electromechanical properties owing to the structural instability and the coexistence of two or more phases. The introduction of Sn additive ions does not seemingly disrupt this phase coexistence to a significant extent, which may further elucidate the observed piezoelectric and ferroelectric characteristics of the system. In our study, we have observed significant improvements in the piezoelectric properties, particularly at wt% = 0.2 composition, and performed a thorough analysis of the structural characteristics, including the lattice constants, distortions, and the relationship between the crystalline size and the density (provided in

Table 1. Structural characteristics of the BFBT:wt%Sn (wt% = 0–0.25) ceramic.

wt% Value of Sn in BFBT	Crystalline Size (D) Nm	Dislocation Density nm−2	Micro Strain	Density ρre (%)
0	48.87	4.19 × 10−4	5.36 × 10−4	94.5
0.1	45.80	4.77 × 10−4	5.71 × 10−4	95
0.15	35.62	7.88 × 10−4	7.36 × 10−4	95.38
0.2	29.25	1.17 × 10−3	8.97 × 10−4	96.6
0.25	36.73	7.41 × 10−4	7.14 × 10−4	95.8

).

As the Sn concentration increases from 0 to 0.2, the crystalline size decreases significantly, reaching a minimum of 29.25 nm at wt% = 0.2. This reduction in the crystalline size can enhance the surface area and improve the piezoelectric properties by facilitating increased domain wall mobility. Concurrently, the dislocation density rises, peaking at wt% = 0.2 with a value of 0.001169 nm⁻², suggesting that the introduction of Sn induces a higher concentration of defects in the crystal structure. These defects can disrupt the long-range order while potentially enhancing the piezoelectric response due to easier domain switching. Additionally, the microstrain increases, also reaching its highest value at wt% = 0.2 (0.000896), indicating local deformation within the lattice. Collectively, these microstructural changes highlight the significant influence of Sn addition on the properties of the BFBT ceramics, suggesting that the optimal composition for enhanced piezoelectric performance may lie at the wt% = 0.2 level.

The morphological analysis of the BFBT:wt%Sn (wt% = 0–0.25) was observed by SEM and is presented in Figure 2a–h, where highly densified micrographs without any porosity of all the ceramic compositions are reported. The grain sizes of the BFBT ceramic show an average of 3–4 µm (Figure 2a), but then it started to reduce with the addition of Sn-ions. For the BFBT:0.2Sn ceramic, the measured grain size is ~1–2 µm (Figure 2c), and such a reduction in the grain size can be associated with overpassing the settled heterogeneity of the BFBT structural stability where Sn-ions have tried to occupy the available lattice sites (created due to the high sintering temperature), and also, SnO₂ possesses a more refractory nature than Bi₂O₃ [29]. The reduction in the grain size of the ceramic can also be accredited to the low melting and Curie temperature of nanosized SnO₂ materials (~300 °C) [30]. The ionic radius of Sn⁴⁺ (~0.69 Å) is much smaller than that of Bi³⁺ (~1.08 Å) [31], making it unlikely that Sn⁴⁺ substitutes for Bi³⁺ at the A-site. Instead, Sn⁴⁺ is more likely to occupy the B-site, substituting for Fe³⁺ or Ti⁴⁺, given the similarity in their ionic radii. The introduction of Sn⁴⁺ at the B-site likely influences the diffusion kinetics during sintering, leading to a reduced grain size, as supported by the absence of secondary phases in the XRD patterns. A similar type of suppression of the grain size of BFBT-based ceramics has been reported earlier [32,33]. For the confirmation of the contribution of all the constituent elements in the BFBT:0.2Sn ceramic, 2D colored elemental mapping is presented in Figure 2e–h. A high degree of dispersion has been observed with uniformity for the Ti (Figure 2f) and Fe (Figure 2g), whereas a low degree of dispersion has been observed for the Sn-ion (Figure 2h) distribution, confirming the low content (0.2 wt%SnO₂) addition of the SnO₂. For a better understanding, a surface morphological image of the BFBT:0.1Sn ceramic is presented in the SI in Figure S2.

For practical applications like non-volatile memory devices and piezoelectric applications, the ferroelectric (polarization vs. electric field) P-E loops of the BFBT:wt%Sn (wt% = 0–0.25) ceramics have been measured (Figure 3a), where the BFBT:0.2Sn ceramic has shown the maximum remnant polarization (P_r ~ 22.68 µC/cm²). The measurements for all the samples were taken at a 0–80 kV/cm electric field and an applied frequency of 10 Hz. In Figure 3b, there is the plot between the coercive electric field for all the BFBT:wt%Sn (wt% = 0–2.5) ceramic compositions. It is observed that for the pristine BFBT, the coercive electric field was ~33kV/cm, but then with the addition of wt%Sn, the value E_C started to reduce. The increment in the ferroelectric domain switching is consistent with the decrement of the Ec with varying Sn-ions. Figure 3c is demonstrating the relationship of the maximum polarization (P_max) and the P_r dependent on the wt% value of the Sn in the BFBT, where it is clearly evident that the values of P_max (~31.86 µC/cm²) and P_r (22.68 µC/cm²) were highest for the BFBT:0.2Sn ceramic as compared to all the other compositions. For BFBT:0.25Sn, the reduction in the P_max (~27.88 μC/cm²) and P_r (~21.57 μC/cm²) can be attributed to the onset of saturation, where the material reaches its solubility limit for Sn-ions in the BFBT matrix. As a result, excessive Sn-ions begin to segregate at the grain boundaries [34], which can disrupt polarization switching and contribute to the reduction in the ferroelectric properties [2,35]. However, the resistivity trend in Figure 4d shows that the 0.25 wt% Sn-added sample still maintains higher resistivity compared to the 0.1 wt% and 0.15 wt% Sn-added samples, indicating that significant leakage current is not the primary cause of the reduced ferroelectric properties. Instead, the decrease in the P_max and P_r may be due to increased structural disorder or grain boundary effects, which limit the full alignment of the domains during polarization switching, consistent with behavior observed in relaxor ferroelectrics.

The piezoelectric coefficient d₃₃, as a function of the wt% values of the Sn in BFBT ceramics, is presented in Figure 4a, where the BFBT:0.2Sn ceramic has demonstrated the highest d₃₃ value of 211 pC/N, much higher than that of the pure BFBT (187 pC/N) ceramic. The incorporation of Sn⁴⁺ into B-site perovskite structures leads to lattice distortions due to the difference in ionic radii between Sn⁴⁺ and its replacement ions, such as Fe³⁺ or Ti⁴⁺. These distortions can modify the local symmetry, induce strain, and enhance the piezoelectric performance. Additionally, Sn⁴⁺ can create oxygen vacancies or ionic defects to maintain charge neutrality, affecting the domain wall motion and piezoelectric response. These distortions can also promote local structural heterogeneity, forming polar nanoregions (PNRs), further enhancing the piezoelectric response in the relaxor state. The d₃₃ has reached a maximum and then reduced for the BFBT:0.25Sn ceramic, which was also observed in the case of the ferroelectric analysis (Figure 3c); hence, the percolation threshold value has been reached, where the additive, after occupying the vacant lattice sites, starts to accumulate at the grain boundaries and results in the creation of a leakage current and the reduction of the d₃₃ values. For the utilization of the reported ceramics in the field of high-temperature piezoelectric devices, it is important to measure the stability of the d₃₃ values with the variation of the temperature. Hence, all the ceramic compositions of BFBT:wt%Sn (wt% = 0–0.25) were annealed from 50 to 600 °C with the step size of 50 °C for 30 min, and later, their d₃₃ values were observed at room temperature and reported in Figure 4b. All the ceramic compositions have demonstrated good and stable piezoelectric behavior until 400 °C, such that the BFBT, BFBT:0.1Sn, BFBT:0.15Sn, BFBT:0.2Sn and BFBT:0.25Sn ceramic samples have displayed d₃₃ values of 98, 105, 130, 150 and 121 pC/N, respectively. Even at 550 °C, the samples have maintained the weak signal of the d₃₃ response; the BFBT:0.2Sn ceramic has displayed the 24 pC/N at 550 °C. Such results confirm the character of the BFBT:0.2Sn ceramic to be employed for high-temperature piezoelectric devices. The impedance values, as a function of the frequency plots for the BFBT:wt%Sn (wt% = 0–0.25) ceramic, are presented in Figure 4c, where it is evident that all the ceramic compositions have maintained their impedance of ~10⁷ Ω at room temperature and a 100 Hz frequency. There came a decrement in the impedance with a variation in the frequency, but it remained a consistent reduction in all the compositions. The same trend of resistivity (~10⁷ Ω) for all the compositions of the BFBT:wt%Sn (wt% = 0–0.25) ceramics is observed at room temperature, and with the variation of the temperature to 500 °C, the resistivity of the ceramics reduced in a similar fashion for all the ceramics, and it became conductive at a high temperature of 500 °C. The high resistivity, high impedance and low dielectric loss at room temperature are the confirmation of lower oxygen vacancies and fewer charge effects even after the sintering at a high temperature of 1010 °C. Such characteristics of the materials are important to fully polarize the ceramics under an applied electric field and useful to utilize in high-temperature piezoelectric applications.

The dielectric constant versus temperature (ε_r vs. T) plots for analyzing the stability of the ceramic compositions and their Curie temperatures are presented in Figure 5a–d. The ε_r vs. T plots are measured for the 15–600 °C temperature range and varying frequencies of 100 Hz, 100 kHz, and 1 MHz. Figure 5a is a presentation of the typical ferroelectric sharp ε_r vs. T peak at a T_C of ~510 °C. As the Sn content is varied, the dielectric constant curves, as a function of the temperature, start to broaden and the frequency is dispersed around their T_C values, indicating the relaxor behavior of the ceramics [36]. This transformation from true ferroelectric to relaxor ferroelectric is associated with the existence of induced polar nanoregions (PNRs) and the structural heterogeneity of the BFBT host matrix created due to the Sn addition [37]. Such PNRs are formed due to the fluctuation of dipoles at the nano-level, which causes the amplification of the piezoelectric response (evident from Figure 4a) [38]. There also comes a gradual decrease in the value of T_C with the variation of the Sn content; for the BFBT:0.15Sn, BFBT:0.2Sn and BFBT:0.25Sn ceramics, the values of T_C are 480 °C, 445 °C and 433 °C, respectively. Figure 5e–h present the dielectric loss versus temperature (tanδ vs. T) plots, and the measurement has demonstrated the low dielectric loss of 0–1 even at the high temperature of 400 °C. The dielectric constant and dielectric loss information of the BFBT:0.1Sn ceramic is presented in SI Figure S3. This strong dielectric stability can be associated with the high density of the ceramic materials, along with the low charge defect concentration, consistent with previously reported rare-earth-modified BFBT ceramic systems [18]. Finally, for the better understanding of presented study, the outcomes are compared with the literature (

Table 2. Comparison of the BFBT:wt%Sn (wt% = 0–0.25) ceramics with the literature.

Sr. No	Ceramic Compositions	d33 pC/N	Pr μC/cm2	Ref.
1	0.7BiFeO3-0.3BaTiO3	191	28.06	[16]
2	0.66BiFeO3-0.34BaTiO3	217	27.3	[17]
3	0.7Bi1.03(1−x)LaxFeO3-0.3BaTiO3	274	~18.5	[18]
4	0.7BiFeO3-0.3BaTiO3	210	40.6	[22]
5	(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 + xSnO2	656	8.98	[26]
6	0.7BiFeO3-0.3BaTiO3	210	31.2	[39]
7	BiFeO3-BaTiO3-0.2wt%SnO2	211	22.68	This Work

), it will provide the better significance of our work for the high-temperature piezoelectric devices.

4. Conclusions

In conclusion, a successful ceramic scheme for BFBT:wt%Sn (wt% = 0–0.25) has been fabricated by using the rapid solid-state reaction mechanism. All the ceramic compositions have maintained their MPB region even after the addition of Sn-ions at the lattice sites of the BFBT host matrix. The BFBT:0.2Sn ceramic composition has shown the best merits as compared to all the other compositions: highest P_r ~ 22.68 µC/cm², impressive d₃₃ ~ 211 pC/N, stable impedance of 1.07 × 10⁷ Ω, and a Curie temperature of 435 °C. BFBT:0.2Sn has maintained an excellent stable d₃₃ of 150 pC/N and resistivity of ~10² Ω even at the high temperature of 400 °C, confirming the potential of the ceramic for high-temperature piezoelectric applications.