Anisotropic effects of oxygen vacancy defects on the electrical properties of highly oriented bismuth titanate ferroelectric ceramics

Bismuth titanate (Bi₄Ti₃O₁₂, BIT) exhibits a high Curie temperature and anisotropic electrical performance owing to its layered perovskite structure, and hence, it is an important ferroelectric material for high-temperature piezoelectric applications. It is crucial to understand the effects of the anisotropy in BIT-based ferroelectrics for developing novel high-temperature piezoelectric materials. In this study, a highly textured BIT ceramic was fabricated using the tape-casting technique from highly grain-oriented BIT platelets prepared by the molten salt method. The textured BIT ceramic showed a dense microstructure and high grain orientation along the (00l) plane with a texturing degree F_00l = 0.86. It exhibited significant anisotropy in the electrical properties along the directions parallel and perpendicular to the axis of the tape-casting plane. Double ferroelectric hysteresis P–E loops and normal ferroelectric P–E loops were observed in the parallel and perpendicular samples, respectively. In addition to the layered crystal structure and domains, the anisotropy in the arrangement of the oxygen vacancy defects and their transport in the structure led to a significant anisotropy in the ferroelectric properties of the textured BIT ceramics. This work demonstrates the anisotropic arrangement of the oxygen vacancy defects and its effect on the electrical properties of high-temperature bismuth layer-structured ferroelectrics.     

Attaining excellent piezoelectric properties and thermal stability in PIN-PHT ceramics by integrating tetragonal phase and relaxor ferroelectrics

Herein, Nd₂O₃-doped 0.11PIN-0.89PHT (PIN-PHT) single-phase tetragonal piezoelectric ceramics are prepared by traditional solid-phase method. In addition, impacts of Nd-doping on crystal structure and electrical performance for 0.11PIN-0.89PHT ceramics are systematically investigated. Based on Landau theory, we propose a novel strategy for obtaining high-performance ceramics by combining tetragonal phase and relaxor ferroelectrics. Results reveal that the introduction of polar nano-regions in tetragonal phase ceramics by doping with rare-earth ions to convert normal ferroelectrics into relaxed ferroelectrics is responsible for excellent properties of 0.11PIN-0.89PHT-xNd ceramics. The optimized comprehensive performance is obtained at x = 0.9 mol%, where d₃₃ = 670 pC/N, S_max = 0.29% (45 kV/cm), strain hysteresis = 8.68% (45 kV/cm), d₃₃* = 736 p.m./V (30 kV/cm), T_C = 312.6 °C, ε_r = 3234, k_p = 0.62, tanδ = 0.014, and excellent high-temperature stability in temperature range of 20–240 °C. After 10⁶ cycles, electrical properties and strain remain unchanged, showing excellent anti-fatigue behavior. This work provides a novel approach for the development of ceramics with outstanding piezoelectric response, high strain, low strain hysteresis, excellent anti-fatigue resistance and thermal stability, and is expected to realize practical applications of piezoelectric ceramics.     

Achieving both high electromechanical properties and temperature stability in textured PMN-PT ceramics

Textured piezoelectric ceramics, such as textured Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) ceramics, have attracted considerable attention from both academia and industry, as they possess crystal-like piezoelectric properties, high composition homogeneity, and low manufacturing cost. However, the main difficulty with the textured piezoelectric ceramics is the presence of BaTiO₃ (BT) templates, which greatly reduces their piezoelectricity and phase transition temperature. Thus, it is highly recommended to fabricate textured piezoelectric ceramics using as few templates as possible. Here, we successfully fabricated high-quality <001>-textured PMN-28PT ceramics (texturing degree of 99%) by using an extremely small amount of BT templates (1 vol.%) with the help of CuO/B₂O₃ sintering aids. The textured PMN-28PT ceramic exhibits 80% piezoelectric coefficient (d₃₃ ∼ 1200 pC/N), 96% electromechanical coefficient (k₃₃ ∼ 88%) and the same temperature stability (T_rt ∼ 100, T_c ∼ 150°C) when compared to its single crystal counterpart. In addition, by using an alternating current electric field poling (AC-poling), the piezoelectric coefficient d₃₃ and dielectric permittivity ε₃₃ of the textured PMN-28PT ceramics were further enhanced around 5–8%. It is believed that the advantages of high electromechanical properties, low cost, and easy mass production of textured PMN-28PT ceramic will make it a promising candidate for advanced electromechanical devices.     

Improving piezoelectric properties and temperature stability for KNN‐based ceramics sintered in a reducing atmosphere

Lead‐free 0.955K_0.5Na_0.5Nb_1‐zTa_zO₃‐0.045Bi_0.5Na_0.5ZrO₃+0.4%MnO ceramics (abbreviated as KNNTaz‐0.045BNZ+0.4Mn) were prepared by a conventional solid‐state sintering method in a reducing atmosphere (oxygen partial pressure of 1 × 10^?10 atm). All ceramics with a pure perovskite structure show the two‐phase coexistence zone composed of rhombohedral and tetragonal phase. Ta⁵⁺ ions substitute for Nb⁵⁺ ions on the B‐site, which results in a decrease in the R phase fraction in the two‐phase coexistence zone. The R‐T phase transition temperature moves to room temperature due to the substitution of Nb⁵⁺ ions by Ta⁵⁺ ions. A complex domain structure composed of small nano‐domains (~70 nm) formed inside large submicron domains (~200 nm) exists in KNNTa0.02‐0.045BNZ+0.4Mn ceramics, which can induce a strong dielectric‐diffused behavior and improve the piezoelectric properties. The temperature stability for the reverse piezoelectric constant for the KNNTaz‐0.045BNZ+0.4Mn ceramics can be improved at z = 0.02. Excellent piezoelectric properties (d₃₃ = 328 pC/N, and  = 475 pm/V at E_max = 20 kV/cm) were obtained for the KNNTa_0.02‐0.045BNZ+0.4Mn ceramics.     

Optical,electrical, and photoelectric properties of nitrogen-doped perovskite ferroelectric BaTiO3 ceramics

Nitrogen-doped BaTiO₃ (BT) ceramics were produced by the solid-state reaction method in conjunction with ammonia gas treatment. The optical absorption spectra results show that the bandgap of BT ceramic is narrowed after N-doping, suggesting that the N-doping is an effective route to increase light absorption. Polar properties measurements indicate that the ferroelectricity of BT ceramic is well maintained after the N-doping. In addition, the electric-field–induced strain is prominently improved to ~0.8% after N-doping, a value superior to that of PZT. Furthermore, the influence of N-doping on photoelectric properties of BT ceramics was also investigated. Large increase in photoconductivity and fast response to light illumination conditions were observed in N-doped BT ceramics. This work provides a novel route to enhance the (photo)electric properties of ferroelectric materials.     

Enhanced piezoelectric properties in BF-BT based lead-free ferroelectric ceramics for high-temperature devices

Due to the high Curie temperature (T_C), BiFeO₃–BaTiO₃ (BF-BT) ceramics have been broadly investigated in high-temperature piezoelectric devices. The piezoelectric constant is one of the most significant factors in determining the sensitivity and reliability of piezoelectric functional components. However, the poor piezoelectric constant (d₃₃) of BF-BT ceramic has prevented the practical application of the material. In this work, we innovatively introduce the 0.93Bi_0.5Na_0.5TiO₃-0.07BaTiO₃ (0.93NBT-0.07BT) component to 0.7BF-0.3BT ceramic, to build a morphotropic phase boundary (MPB) for enhancing d₃₃. The XRD analysis shows that the (0.7BF-0.3BT)-x(0.93NBT-0.07BT) ceramics are still in the MPB region with R–PC phases coexistence, and exhibits a homogeneous solid solution. Moreover, the introduction of 0.93NBT-0.07BT ceramic suppresses the generation of defects and facilitates grain growth, thus enhancing piezoelectric property. In consequence, an optimum piezoelectricity d₃₃ = 213 pC/N along with T_c～450 °C was obtained in (0.7BF-0.3BT)-0.01(0.93NBT-0.07BT). This research provides a new idea for the application of BF-BT ceramics in high-temperature piezoelectric devices.     

The surface mechanism for the flexoelectric response in sodium bismuth titanate-based ferroelectric ceramics

The flexoelectric effect of the ferroelectric materials has been intensively studied in recent years. One unresolved issue in this field is that the measured flexoelectric coefficients in ferroelectrics are often several orders of magnitude greater than the values predicted by the theoretical studies. To understand the mechanism for this discrepancy, the flexoelectric response of the Na_0.5Bi_0.5TiO₃–BaTiO₃ (NBBT) ceramics of different compositions was systematically studied. We show that the measured flexoelectric response of the NBBT ceramics is mainly from the piezoelectric response of the spontaneously polarized surface in the ceramics. The surface effect can be reduced or removed by abrading the surface off or modifying the compositions of the surface. The thickness of the surface layer was found to be 10-15 µm. We also show that the composition dependence of the flexoelectric response is mainly affected by the piezoelectric response of the surface layer, whereas the temperature dependence of the flexoelectric response of a composition is primarily influenced by the dielectric constant of the bulk. The mechanisms for the observations are discussed based on the origin of the surface layer. This work is important for the understanding of the mechanisms of the flexoelectric (or flexoelectric-like) response in ferroelectrics.     

Processing and electromechanical properties of high-coercive field ZnO-doped PIN-PZN-PT ceramics

This study explores sintering and piezoelectricity of ZnO-doped perovskite Pb(In_1/2Nb_1/2)O₃-Pb(Zn_1/3Nb_2/3)O₃-PbTiO₃ (PIN-PZN-PT) ceramics. The enhanced densification of ZnO-doped PIN-PZN-PT is attributed to the formation of oxygen vacancies by the incorporation of Zn²⁺ into the perovskite B-site and increased rate of bulk diffusion relative to undoped PIN-PZN-PT. Incorporation of Zn²⁺ into the perovskite lattice increased the tetragonal character of PIN-PZN-PT as demonstrated by tetragonal peak splitting and increased Curie temperature. Sintering in flowing oxygen reduced the solubility of Zn²⁺ in the perovskite lattice and resulted in rhombohedral PIN-PZN-PT. Sintering in oxygen prevented secondary phase formation which resulted in a high-piezoelectric coefficient (d₃₃ – 550 pC/N), high-coercive field (E_c – 13 kV/cm), and high-rhombohedral to tetragonal phase transition temperature (T_r-t – 165°C). We conclude that ZnO-doped PIN-PZN-PT ceramics are excellent candidates for high-power transducer applications.     

Temperature stability and electrical properties of MnO‐doped KNN‐based ceramics sintered in reducing atmosphere

Lead‐free MnO‐doped 0.955K_0.5Na_0.5NbO₃‐0.045Bi_0.5Na_0.5ZrO₃ (abbreviate as KNN‐0.045BNZ) ceramics have been prepared by a conventional solid‐state sintering method in reducing atmosphere. The MnO addition can suppress the emergence of the liquid phase and improve the homogenization of grain size. All ceramics sintered in reducing atmosphere show a two‐phase coexistence zone composed of rhombohedral (R) and tetragonal (T) phase. MnO dopant results in the content increase in R phase and slight increase in Curie temperature T_C. For KNN‐0.045BNZ ceramics, Mn²⁺ ions preferentially occupy the cation vacancies in A‐site to decrease oxygen vacancy concentration for 0.2%‐0.4% MnO content, whereas Mn²⁺ ions substitute for Zr⁴⁺ ions in B‐site to form oxygen vacancies at x ≥ 0.5. The defect dipole is formed at the moderate concentration from 0.5 to 0.6, which can provide a preserve force to improve the temperature stability of piezoelectric properties for k_p and . The Mn0.4 ceramics show excellent electrical properties with quasistatic piezoelectric constant d₃₃ = 300 pC/N, electromechanical coupling coefficient k_p = 51.2%, high field piezoelectric constant  = 430 pm/V (at E_max = 25 kV/cm) and T_C = ~345°C, insulation resistivity ρ  =  6.13 × 10¹¹ Ωcm.     

Piezoelectric and ferroelectric properties of (Bi,Na)TiO3–(Bi,Li)TiO3–(Bi,K)TiO3 ceramics for accelerometer application

The piezoelectric and ferroelectric properties of 0.76(Bi_0.5Na_0.5)TiO₃–0.04(Bi_0.5Li_0.5)TiO₃–0.2(Bi_0.5K_0.5)TiO₃ (abbreviated as 0.76BNT–0.04BLT–0.2BKT) ceramics were investigated to clarify the optimal sintering temperature, and the vibration characteristics were examined for a compression‐mode accelerometer assembly in which 0.76BNT–0.04BLT–0.2BKT ceramics sintered at the optimized temperature served as the piezoelectric elements. The increase in the grain size of the 0.76BNT–0.04BLT–0.2BKT ceramics with the sintering temperature provides a beneficial contribution to the piezoelectric coefficient; however, it detrimentally contributes to the depolarization temperature. The charge sensitivity of the prototype accelerometers was evaluated with changes in the seismic mass and the layer number of the piezoceramics. The deviation between the theoretical and measured values of charge sensitivity was less than 10%.     

Significantly enhanced dc electrical resistivity and piezoelectric properties of Tb-modified CaBi2Nb2O9 ceramics for high-temperature piezoelectric applications

Bismuth layer–structured ferroelectric calcium bismuth niobate (CaBi₂Nb₂O₉, CBN) is considered to be one of the most potential high-temperature piezoelectric materials due to its high Curie temperature T_c of ∼940°C, but the drawbacks of low electrical resistivity at elevated temperature and low piezoelectric performance limit its applications as key electronic components at high temperature (HT). Herein, we report significantly enhanced dc electrical resistivity and piezoelectric properties of CBN ceramics through rare-earth element Tb ions compositional adjustment. The nominal compositions of Ca_1−xTb_xBi₂Nb₂O₉ (abbreviated as CBN-100xTb) have been fabricated by conventional solid-state reaction method. The composition of CBN-3Tb exhibits a significantly enhanced dc electrical resistivity of 1.97 × 10⁶ Ω cm at 600°C, which is larger by two orders of magnitude compared with unmodified CBN. The donor substitutions of Tb³⁺ ions for Ca²⁺ ions reduce the oxygen vacancy concentrations and increase the band-gap energy, which is responsible for the enhancement of dc electric resistivity. The temperature-dependent dc conduction properties reveal that the conduction is dominated by the thermally activated oxygen vacancies in the low-temperature region (200–350°C) and by the intrinsic conduction in the HT region (350–650°C). The CBN-3Tb also exhibits enhanced piezoelectric properties with a high piezoelectric coefficient d₃₃ of ∼13.2 pC/N and a high T_c of ∼966°C. Moreover, the CBN-3Tb exhibits good thermal stabilities of piezoelectric properties, remaining 97% of its room temperature value after annealing at 900°C. These properties demonstrate the great potentials of Tb-modified CBN for high-temperature piezoelectric applications.     

Crosslinked,biodegradable polyurethanes for precision-porous biomaterials: Synthesis and properties

Crosslinked poly(ester urethane)s and their acrylate derivatives based on trifunctional polycaprolactone and trifunctional aliphatic isocyanates were synthesized. Biodegradable scaffolds with uniform, controlled micron-scale porosity were fabricated with these materials. Mechanical and swelling properties of monolithic and microporous materials were studied. Cytotoxicity, hydrolytic, and enzymatic degradation and their effects on mechanical properties of the biodegradable scaffolds were investigated. The polymer degradation products were found not to be cytotoxic at moderate concentrations and to permit cell attachment and spreading. Degradation rates and mechanical properties could be tuned to desired performance criteria for a given application by adjusting crosslink density and the ratio of hard segment to soft segment. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48943.     

Improved transmittance and ferroelectric properties realized in KNN ceramics via SAN modification

Transparent, Sr(Al_0.5Nb_0.5)O₃‐modified K_0.5Na_0.5NbO₃ (KNN) ceramics were successfully fabricated by a solid‐state pressureless sintering method in this work. The obtained microstructure, transmittance, and electrical properties were characterized in detail. Our results indicated that the modification by Sr(Al_0.5Nb_0.5)O₃ significantly limited the grain growth behavior of KNN, resulting in dense ceramics with submicron grain size (<0.5 μm) and small pore size. Consequently, the ceramic with the 0.96K_0.5Na_0.5NbO₃‐0.04Sr(Al_0.5Nb_0.5)O₃ composition showed superior transmittance and electrical properties: T = 55% in the visible region (0.78 μm), d₃₃ = 105 pC/N, ε_r = 1021, and P_r = 15.1 μC/cm², which were significantly higher than those of pure KNN. Our findings implied that the addition of Sr(Al_0.5Nb_0.5)O₃ could be a good strategy to obtain superior transmittance and electrical properties in KNN and may shed light on other ferroelectric systems.     

Superior ferroelectric properties and enhanced depolarization temperature simultaneously achieved in BNT-based ceramics

Bi_0.5Na_0.5TiO₃-based ceramics with high remnant polarization P_r have shown outstanding potential in the application of high-power ferroelectric transducers. However, low depolarization temperature T_d is an obstacle for their application. Here, a composition design strategy was proposed to simultaneously improve the T_d and P_r in BNT-based materials. Ultrahigh P_r of 40.56 µC/cm² and relative high T_d of 184°C were synergistically achieved in (Bi_0.5Na_0.5)(Ti_0.995Mn_0.005)O₃ (BNMT) ceramics by adding 1.0 mol% BiGaO₃ (BG), which is superior to other reported lead-free systems. The excellent ferroelectric properties were attributed to strengthen ferroelectric order as evidenced by increased rhombohedral distortion. Meanwhile, the enhanced depolarization temperature, increasing from 168°C for x = 0% to 184°C for x = 1.0%, can be ascribed to the suppression of the thermal-induced ferroelectric-relaxor phase transition by adding BG. Those results enable the BNMT-BG systems ceramics to be an attractive candidate for application in high-power supplies.     

Thermal stability and electric‐field‐induced strain behaviors for PIN‐PSN‐PT piezoelectric ceramics

Pb (In_1/2Nb_1/2) O₃‐Pb (Sc_1/2Nb_1/2) O₃‐PbTiO₃ (PIN‐PSN‐PT) ternary ceramics with compositions near morphotropic phase boundary (MPB) were fabricated by solid‐state‐sintering process. Dielectric and piezoelectric properties of xPIN‐yPSN‐zPT (x = 0.19, 0.23 and z = 0.365, 0.385) ceramics were investigated as a function of temperature, showing high T_r‐t and T_c on the order of 160 ~ 200°C and 280 ~ 290°C, respectively. The xPIN‐yPSN‐0.365PT (x = 0.19 and 0.23) ceramics do not depolarize at the temperature up to 200°C, showing a better thermal stability when compared to the state‐of‐the‐art relaxor‐PbTiO₃ systems. A slight variation (<9%) of k_p, k_t, and k₃₃ was observed in the temperature range of 25°C‐160°C for xPIN‐yPSN‐0.385PT (x = 0.19 and 0.23) ceramics. Rayleigh analysis was employed to quantify the contribution of domain wall motion to piezoelectric response, where the domain wall contribution was found to increase with composition approaching MPB for PIN‐PSN‐PT system.     

Textured CaBi4Ti4O15 ceramics with large piezoelectricity,excellent thermal stability and high resistivity

The bismuth layer-structured ferroelectrics (BLSF) are promising high-temperature piezoelectric materials, in which large piezoelectricity, good thermal stability and high electrical resistivity are desired. Here highly textured CaBi₄Ti₄O₁₅ BLSF ceramics with orientation factor of 82% have been fabricated by spark plasma sintering technique. The piezoelectric coefficient d₃₃ is significantly enhanced by 250%, from 7.2 pC/N for the texture-less sample to 25.3 pC/N for the textured one, accompanied by a high Curie temperature T_C= 788 °C. The variation of d₃₃ is below 5% in the temperature range of 25–500 °C, showing excellent thermal stability. The textured sample exhibits high electrical resistivity ρ = 2.1 × 10¹¹ Ω·cm, an order of magnitude larger than that of the texture-less sample. At the temperature as high as 500 °C, the textured sample still maintains excellent electrical properties of d₃₃ = 24.2 pC/N, tanδ = 9.9% and ρ = 2.7 × 10⁶ Ω·cm, suggesting that the textured CaBi₄Ti₄O₁₅ ceramics could be a potential candidate for high-temperature piezoelectric sensor or detector applications.     

PZT-nickel ferrite and PZT-cobalt ferrite comparative study: Structural,dielectric, ferroelectric and magnetic properties of composite ceramics

Comparative study of different PZT-based composite materials ((x)PbZr_0.52Ti_0.48O₃ + (1-x)CoFe₂O₄ and (x)PbZr_0.52Ti_0.48O₃ +(1-x)Ni_0.7Zn_0.3Fe₂O₄ (x = 0.8 and 0.9)) is presented in the frame of structural, dielectric, ferroelectric and magnetic properties. PZT and NZF/CF powders were synthesized by auto combustion technique. The composites were synthesized by mixing the appropriate amount of individual phases using conventional sintering. XRD data indicated the formation of well crystallized structure of PZT and NZF/CF, without the presence of undesirable phases. SEM micrographs revealed a uniform grain distribution of both, ferroelectric and ferromagnetic phases. Non-saturated hysteresis loops are evident in all samples due to the existence of non-ferroelectric ferrite phase. All the samples exhibit typical ferromagnetic hysteresis loop, indicating the presence of the order magnetic structure. Dielectric investigations revealed that ferrites are the main source of charge carriers, which must be of electronic origin. The activation energy of effective electrical resistivity is heavily influenced by the ferroelectric phase.     

Defect‐driven evolution of piezoelectric and ferroelectric properties in CuSb2O6‐doped K0.5Na0.5NbO3 lead‐free ceramics

Defect greatly affects the microscopic structure and electrical properties of perovskite piezoelectric ceramics, but the microscopic mechanism of defect‐driven macroscopic properties in the materials is not still completely comprehended. In this work, K_0.5Na_0.5NbO₃+x mol CuSb₂O₆ lead‐free piezoelectric ceramics were fabricated by a solid‐state reaction method and the defect‐driven evolution of piezoelectric and ferroelectric properties was studied. The addition of CuSb₂O₆ induces the formation of dimeric (DC1) and trimeric (DC2) defect dipoles. At low doping concentration of CuSb₂O₆ (0.5‐1.0 mol%), DC1 and DC2 coexist in the ceramics and harden the ceramics, inducing a constricted double P‐E loop and high Q_m of 895 at x=0.01. However, DC2 becomes more dominant in the ceramics with high concentration of CuSb₂O₆ (≥1.5 mol%) and thus leads to softening behavior of piezoelectricity and ferroelectricity as compared to the ceramic with x=0.01, giving a single slanted P‐E loop and relatively low Q_m of 206 at x=0.025. All ceramics exhibit relatively high d₃₃ of 106‐126 pC/N. Our study shows that the piezoelectricity and ferroelectricity of K_0.5Na_0.5NbO₃ ceramics can be tailored by controlling defect structure of the materials.     

Effect of La and Ni substitution on structure,dielectric and ferroelectric properties of BiFeO3 ceramics

In this communication, we present the results on Bi_1−xLa_xFe_1−yNi_yO₃ (x=0.0, 0.1; y=0.0, 0.05) samples processed by solid-state reaction route in order to study crystalline and electronic structure, dielectric and ferroelectric properties. The best refinement was achieved by choosing rhombohedral structure (R3c) for BiFeO₃ and Bi_0.9La_0.1FeO₃ samples. Whereas, the XRD pattern of BiFe_0.95Ni_0.05O₃ and Bi_0.9La_0.1Fe_0.95Ni_0.05O₃ samples were refined by choosing rhombohedral (R3c) and cubic (I23) structure. Raman scattering measurement infers nine Raman active phonon modes for all the as prepared samples. The substitution of Ni ion at Fe-site in BiFeO₃ essentially changes the modes position i.e. all the modes are observed to shift to lower wave number. Dielectric constant (ε′) and dielectric loss (tan δ) as a function of frequency have been investigated and they decreases with increasing frequency of the applied alternating field and become constant at high frequencies. This feature is a characteristic of Maxwell Wagner type of interfacial polarization. The remnant polarization (P_r) for Bi_0.9La_0.1FeO_3, BiFe_0.95Ni_0.05O₃, and Bi_0.9La_0.1Fe_0.95Ni_0.05O₃ are 0.08, 0.11, 0.69 μC/cm², respectively and the value of coercive field for Bi_0.9La_0.1FeO_3, BiFe_0.95Ni_0.05O₃, and Bi_0.9La_0.1Fe_0.95Ni_0.05O₃ are 0.53, 0.67, 0.68 kV/cm, respectively. X-ray absorption spectroscopy (XAS) experiments at Fe L₂,₃ and O K-edges are performed to investigate the electronic structure of well-characterized Bi_1−xLa_xFe_1−yNi_yO₃ (x=0.0, 0.1; y=0.0, 0.05) samples. The presence of reasonable ferroelectric polarization at room temperature in Bi_0.9La_0.1Fe_0.95Ni_0.05O₃ ceramics makes it suitable for technological applications.