Influence of Primary Milling on Structural and Electrical Properties of Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> Ceramics Obtained by Sintering Process

In this article, the influence of primary mechanical milling of precursors on the microstructure and dielectric properties of Bi₄Ti₃O₁₂ ceramics was studied. Precursor material (mixture of Bi₂O₃ and TiO₂ powders) was ground by a high-energy attritorial mill for (1, 3, 5, and 10) h. Bi₄Ti₃O₁₂ ceramics were obtained by a solid-state reaction process, synthesized at an intermediate temperature (800 °C) and finally sintered at high temperature (1140 °C). Structure studies were performed by X-ray diffraction (XRD) and scanning electron microscopy techniques. XRD patterns were analyzed by the Rietveld method using the DBWS 9807a program. The thermal properties of the studied materials were measured using differential thermal analysis and thermal gravimetric techniques. These studies indicate that one-, three-, and five-hour primary high-energy ball milling followed by sintering is a promising technique for pure Bi₄Ti₃O₁₂ ferroic ceramics preparation. The investigation of Bi₄Ti₃O₁₂ shows that ceramics obtained from a precursor and milled for 5 h have the best dielectric properties.     

Synthesis,microstructure and microwave dielectric properties of Ca<Subscript>4-x</Subscript>Mg<Subscript>x</Subscript>La<Subscript>2</Subscript>Ti<Subscript>5</Subscript>O<Subscript>17</Subscript> ceramics

Ca_4-xMg_xLa₂Ti₅O₁₇ ceramics were prepared by a solid state ceramic route for x = 0, 0.5, 1, 2, 3 and 4. The structure and microstructure of the ceramics were investigated using X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. X-ray diffraction results show that the Ca_4-x Mg _x La₂Ti₅O₁₇ adopts an orthorhombic crystal structure with no secondary phase observed for x from 0 to 0.5. Secondary phase, MgTiO₃ occurs with further increasing doping level (1 ≤ x ≤ 3). When x = 4, mixture phases La_0.66TiO_2.993, MgTiO₃ and a trace of unknown phase coexist. Ca₄La₂Ti₅O₁₇ ceramic exhibits a relative permittivity (ε_r) ~ 65, quality factor (Q × f) ~13,338 GHz (at ~4.75 GHz), and temperature coefficient of resonant frequency (τ _f ) ~ 165 ppm/°C. The sintering temperature was distinctly reduced from 1,580 °C for x = 0 to 1,350 °C for x = 4. With increasing Mg content, ε_r and τ_f obviously decrease, while Q × f value initially decreases and then increases. The ceramic for x = 2 shows ε_r ~ 50, Q × f ~ 9,451 and τ _f  ~ 62.5 ppm/°C. By the complete replacement of Ca with Mg, Mg₄La₂Ti₅O₁₇ ceramic sintered at 1,350 °C for 4 h combines a high dielectric permittivity (ε _r  = 31), high quality factor (Q × f ~ 15,021) and near-zero temperature coefficient of resonant frequency (τ _f  ~ 4.0 ppm/°C). The materials are suitable for microwave applications.     

Relationship among the phase equilibria,microstructures, and dielectric properties of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics via different sintering time

The structure–property relationship of the CaCu₃Ti₄O₁₂ ceramics processed via conventional solid-state method was studied in terms of the different processing conditions. X-ray diffraction patterns of the tenorite CuO and cuprite Cu₂O secondary phases found on the unpolished and polished surfaces of CaCu₃Ti₄O₁₂ were explained by the reduction/reoxidation reaction as a function of sintering time. Based on the microstructures, grain growth of CaCu₃Ti₄O₁₂ continued from 0.5 to 4 h sintering while the further growth was limited to the small-sized grains after 8 h sintering. Also, WDS data indicated the Cu-deficient and Ti-excessive stoichiometry of CaCu₃Ti₄O₁₂ on both outer and inner regions regardless of sintering time. The change of dielectric constant and tan δ were shortly discussed with regard to the secondary phases and the microstructures of the different sintering hours.     

Influence of Sm substitution on the phase,microstructure and microwave dielectric properties of SrLa<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>17</Subscript>

New dielectric ceramics in the SrLa_4−xSm_xTi₅O₁₇ (0 ≤ x ≤ 4) composition series were prepared through a solid state mixed oxide route to investigate the effect of Sm⁺³ substitution for La⁺³ on the phase, microstructure and microwave dielectric properties. At x = 0–3, all the compositions formed single phase ceramics within the detection limit of in-house X-ray diffraction when sintered in the temperature range 1500–1580 °C. At x = 4, a mixture of Sm₂Ti₂O₇ and SrTiO₃ formed. The maximum Sm⁺³-containing single phase ceramics, SrLaSm₃Ti₅O₁₇, exhibited relative permittivity (ε_r) = 42.6, temperature coefficient of resonant frequency (τ _f ) = −96 ppm/^oC and quality factor (Q _u f _o ) = 7332 GHz. An analysis of results presented here indicates that SrLa_4−xSm_xTi₅O₁₇ ceramics, exhibiting τ _f  ~ 0 and ε_r ~ 53 could be achieved at x ~ 1.4 but at the cost of decrease in Q _u f _o .     

Effects of Nd-substitution on microstructures and dielectric characteristics of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics

Ca_1−3x/2Nd _x Cu₃Ti₄O₁₂ (x = 0, 0.1, 0.2) ceramics were prepared by a solid state reaction process, and single-phased structures were obtained for all the compositions. The dielectric characteristics of pure and Nd-substituted CaCu₃Ti₄O₁₂ ceramics were investigated together with the microstructures. The mixed-valent structures of Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺ in the present ceramics were confirmed by X-ray photoelectron analysis. The dielectric relaxation in the low temperature range was examined in detail and the variation of dielectric constant and dielectric loss was attributed to the modification mixed-valent structures.     

Phase,microstructural characterization and dielectric properties of Ca-substituted Sr<Subscript>5</Subscript>Nb<Subscript>4</Subscript>TiO<Subscript>17</Subscript> ceramics

The effect of Ca substitution for Sr on the phase, microstructure and microwave dielectric properties of the Sr_5−x Ca _x Nb₄TiO₁₇ composition series was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), an LCR meter, and vector network analyzer. Below 1450 °C, Sr_5−x Ca _x Nb₄TiO₁₇ (x = 1, 2, 3, or 4) compositions formed single-phase Sr₄CaNb₄TiO₁₇, Sr₃Ca₂Nb₄TiO₁₇, Sr₂Ca₃Nb₄TiO₁₇, and SrCa₄Nb₄TiO₁₇ ceramics, respectively. At x = 0 and 5, Sr₅Nb₄TiO₁₇ and Ca₅Nb₄TiO₁₇ formed, but along with Sr₂Nb₂O₇ (at x = 0) and CaNbO₃ and CaNb₂O₆ (at x = 5) secondary phases. Above 1450 °C, all the compositions formed two-phase ceramics. At low frequencies, a phase transition was observed in the composition Sr₅Nb₄TiO₁₇. The substitution of Ca for Sr enabled processing of highly dense Sr₂Ca₃Nb₄TiO₁₇, with ε_r ~ 53.4, τ_f ~ −6.5 ppm/°C and Q _u  × f _o  ~ 1166 GHz. Further investigations are required to improve the quality factor of these ceramics for possible microwave applications.     

Effects of ZnO and CeO2 additions on the microstructure and dielectric properties of Mn-modified (Bi0.5Na0.5)0.88Ca0.12TiO3 ceramics

The effects of ZnO and CeO₂ on the microstructure and dielectric temperature characteristics of the Mn-modified (Bi_0.5Na_0.5)_0.88Ca_0.12TiO₃ ceramics were investigated to develop temperature-stable dielectric ceramics. By adding 1–2 wt% ZnO, the overall dielectric constant increased. With further increasing the amount of ZnO, the dielectric constant at temperatures lower than 25 °C decreased, whereas the dielectric constant at temperatures higher than 75 °C increased. The temperature characteristic of capacitance became flatter when more than 4 wt% ZnO was doped. By adding CeO₂, the dielectric constant decreased and a flat temperature characteristic of permittivity was obtained. X-ray diffraction analysis revealed that the perovskite BNT phase formed for all the compositions and the secondary phases Zn₂TiO₄ and Bi₂Ti₂O₇ occurred, respectively when ZnO and CeO₂ was added. Scanning electron microscope indicated that an inhomogeneous microstructure comprising fine and rectangle grains was observed in the ZnO-free sample. ZnO less than 2 wt% could inhibit the grain growth and decrease long grains. However, the grain growth was promoted as more than 8 wt% ZnO was added. The dielectric loss with different contents of ZnO and CeO₂ were characterized as the function of temperatures for potential use at high temperature. The dielectric loss at 25 °C was independent of the amounts of ZnO and CeO₂. However, the dielectric loss at 250 °C decreased by adding 1 wt% ZnO and then increased with increasing ZnO. This system is considered to be a potential material for high-temperature capacitors.     

Microstructures and microwave dielectric properties of low-temperature sintered Ca2Zn4Ti15O36 ceramics

Low-temperature sintered Ca₂Zn₄Ti₁₅O₃₆ microwave dielectric ceramic was prepared by conventional solid state reaction method. The influences from V₂O₅ addition on the sintering behavior, crystalline phases, microstructures and microwave dielectric properties were investigated. The crystalline phases and microstructures of Ca₂Zn₄Ti₁₅O₃₆ ceramic with V₂O₅ addition were investigated by X-ray diffraction, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). V₂O₅ addition lowered the sintering temperature of Ca₂Zn₄Ti₁₅O₃₆ ceramics from 1140 °C to 930 °C. Ca₂Zn₄Ti₁₅O₃₆ ceramic with 5wt% V₂O₅ addition could be densified well at 930 °C, and showed good microwave dielectric properties of ε_r ~ 46, Q × f ~ 13400 GHz, and temperature coefficient of resonant frequency (τ_f) ~ 164 ppm/°C.

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Dielectric and Structural Properties of Bi<Subscript>5</Subscript>Ti<Subscript>3</Subscript>FeO<Subscript>15</Subscript> Ceramics Obtained by Solid-State Reaction Process from Mechanically Activated Precursors

Bi₅Ti₃FeO₁₅ (BTFO), an Aurivillius compound, was synthesized via sintering the Bi₂O₃ and Fe₂O₃ mixture and TiO₂ oxides. The precursor material was ground in a high-energy attritorial mill for (1, 3, 5, and 10) h. The orthorhombic system Bi₅Ti₃FeO₁₅ ceramics was obtained by a solid-state reaction process at 1313 K. Phase formation behavior was investigated using differential thermal analysis (DTA), thermal gravimetric (TG), and X-ray diffraction (XRD) techniques. The frequency-dependent properties of the material were investigated by impedance spectroscopy. The impedance spectroscopic method is widely used to characterize electrical properties of materials and their interfaces with electronically conducting electrodes. These studies indicate that 1h, 3h, and 5h primary high-energy ball milling followed by sintering is a promising technique for pure Bi₅Ti₃FeO₁₅ ceramic preparation, whereas the ceramics obtained from the substrates after 10h milling is a two-phase material. As the result of this investigation, the model of adjusting the Nyquist charts with a three-element R-CPE (constant phase element) series connection was proposed. It was found that the value of the dielectric constant at the Curie temperature decreases when the milling time of the substrates increases. The decrease in the dielectric constant is influenced by the great dispersion of the grains, their dense packing, and location of particular grains in relation to other grains. Moreover, the change of resistivity with frequency indicates that relaxation processes take place in the material. In conclusion, it was reported that the optimal milling time of precursor oxide powders for carrying out the sintering process is equal to 5 h. Then the obtained ceramics contain one phase and exhibit the highest dielectric properties for practical applications.     

Synthesis and characterization of BaTiO<Subscript>3</Subscript>-based X9R ceramics

The effects of (Na_0.5Bi_0.5)TiO₃ (NBT) and MgO addition on the dielectric properties and microstructures of BaTiO₃ (BT) ceramics were investigated. NBT was first added to Nb₂O₅-doped BT system. As NBT content increases from 0 to 0.2 mol, the Curie temperature of the systems shifts to high temperatures and dielectric constant peak at T _c is suppressed evidently. The variation of capacity (ΔC/C _20 °C (%)) of the system at 200 °C decreases with increasing NBT content from 0.1 to 0.2 mol, but that of −55 and 125 °C increases monotonously. The stable temperature characteristics of the dielectric properties improved by NBT doping would be connected with the distortion and deformation of the structure induced by substitution of Na⁺ and Bi³⁺ into Ba sites. MgO was employed to further flatten the ΔC/C _20 °C–T curve. It is very helpful for this ceramic system to satisfy the requirement of EIA-X9R specification on ΔC/C _20 °C and still keep a satisfied dielectric constant. The addition of MgO improved effectively the temperature stability of the dielectric properties. Changes of the crystalline structure and microstructure induced by MgO doping might contribute to these improvements.     

Structural and electric properties of (Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>)<Subscript>0.88</Subscript>Ba<Subscript>0.12</Subscript>TiO<Subscript>3</Subscript>

Lead-free (Na_0.5Bi_0.5)_0.88Ba_0.12TiO₃ ceramics have been prepared and studied by X-ray diffraction and by the complex dielectric response as a function of temperature, frequency and a.c. field intensity. Relaxor-like dielectric behaviour were induced by barium Ba dopping to Na_0.5Bi_0.5TiO₃. It was shown, that relaxor-like characteristics can be enhanced by the increase of the a.c. field intensity. A sharp increase in the electric permittivity and dielectric loss on heating near 230 °C has been observed. This sharp increase in dielectric responses indicates a transformation between classical and relaxor ferroelectric phases. The X-ray diffraction study shows that this transformation corresponds to the first order phase transition from tetragonal to cubic. The use of (Na_0.5Bi_0.5)_0.88Ba_0.12TiO₃ ceramics for device applications has been indicated.     

Giant dielectric and electrical properties of sodium yttrium copper titanate: Na<Subscript>1/2</Subscript>Y<Subscript>1/2</Subscript>Cu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript>

The electrical properties and dielectric response in Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramic prepared by conventional solid-state reaction method and sintered at 1,090 °C for 5 h were investigated as functions of frequency and temperature. Main phase of Na_1/2Y_1/2Cu₃Ti₄O₁₂ with CaCu₃Ti₄O₁₂-like crystallographic structure and CuO secondary phase were observed in the X-ray diffraction pattern. Abnormal grain growth was observed just as observed in CaCu₃Ti₄O₁₂ ceramics. The Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramic exhibits a high ε′ of ~2.04 × 10⁴ at 20 °C and 1 kHz and low tan δ (with the minimum 0.080 at 5 kHz). Impedance spectroscopy analysis reveals that Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramic is electrically heterogeneous, consisting of semiconducting grains and insulating grain boundaries. Giant ε′ response in Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramic is therefore attributed to an internal barrier layer capacitor effect.     

The Development of Microstructure and Ferroelectric Properties of Bi<Subscript>4</Subscript>Ti<Subscript>3.96</Subscript>Nb<Subscript>0.04</Subscript>O<Subscript>12</Subscript> Thin Films

Bi₄Ti_3.96Nb_0.04O₁₂ thin films were successfully deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by a sol–gel method and rapid thermal annealing. The effects of Nb-substitution and annealing temperature (500–800°C) on the microstructure and ferroelectric properties of bismuth titanate thin films were investigated. X-ray diffraction analysis reveals that the intensities of (117) peaks are relatively broad and weak at annealing temperatures smaller than 700°C. With the increase of annealing temperature from 500°C to 800°C, the grain size of Bi₄Ti_3.96Nb_0.04O₁₂ thin films increases. The Bi₄Ti_3.96Nb_0.04O₁₂ thin films annealed at 700°C exhibit the highest remanent polarization (2P _r), 36 μC/cm² and lowest coercive field (2E _c), 110 kV/cm. The improved ferroelectric properties can be attributed to the substitution of Nb⁵⁺ to Ti⁴⁺ in Bi₄Ti₃O₁₂ assisting the elimination of defects such as oxygen vacancy and vacancy complexes.     

Large strain response in acceptor- and donor-doped Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-based lead-free ceramics

Effects of Fe and La addition on the dielectric, ferroelectric, and piezoelectric properties of Bi_0.5Na_0.5TiO₃–Bi_0.5Li_0.5TiO₃–BaTiO₃–Mn ceramics were investigated. Similar to the doping effect in lead-based piezoelectric materials, here the Fe-doped ceramic created a hard effect with an improved mechanical quality factor (Q _m) ~ 160, coercive field (E _c) ~ 2.9 kV/mm, decreased dielectric constant ( e₃₃^T /e₀ ) ~ 80 3, \left( {\varepsilon_{33}^{T} /\varepsilon_{0} } \right)\sim 80 3, and loss (tanδ) ~ 0.024 while the La-doped one indicated a soft feature with improved piezoelectric constant (d ₃₃) ~ 184 pC/N, e₃₃^T /e₀   ~ 983, \varepsilon_{33}^{T} /\varepsilon_{0} \,\sim { 983}, tanδ ~ 0.033, and decreased E _c ~ 2.46 kV/mm. In addition, the temperature dependence of the ferroelectric hysteresis loops and strain response under unipolar electric field was also studied. Around the depolarization temperature T _d, large strain value was obtained with the normalized d₃₃^* d_{33}^{*} up to ~1,000 pC/N, which was suggested originated from the development of the short-range order or non-polar phases in the ferroelectric matrix. All these would provide a new way to realize high piezoelectric response for practical application in different temperature scale.     

Effect of Pb(Ti,Sn)O<Subscript>3</Subscript> on the dielectric properties of high dielectric constant X8R BaTiO<Subscript>3</Subscript>-based ceramics

The high dielectric constant X8R dielectric materials could be sintered at 1,240 °C by doping 2.5 mol% Pb(Ti,Sn)O₃ additives into the BaTiO₃ ceramics, with a dielectric constant greater than 3,400 at 25 °C, dielectric loss lower than 2.0% and temperature coefficient of capacitance (TCC) less than ±15% from −55 to 150 °C, which satisfied X8R specification. The effects of Pb(Ti,Sn)O₃ on the microstructure and dielectric properties of BaTiO₃-based ceramics were investigated. Doped with Pb(Ti,Sn)O₃ additives, the partial solid solution was formed between Pb(Ti,Sn)O₃ and BaTiO₃. Due to the high Curie point of Pb(Ti,Sn)O₃, the Curie point of the ceramics was markedly shifted to higher temperature about 150 °C, and the temperature coefficient of capacitance curves was flattened. The increase of the tetragonality (c/a ratio) and the fine microstructure were resulted in the increase of dielectric constant. With Pb(Ti, Sn)O₃ content up to 3 mol%, the depression of Ti⁴⁺’s polarization and the decrease of the tetragonality (c/a ratio) were resulted in the decrease of dielectric constant.     

Low-temperature sintering and microwave dielectric properties of MgTiO<Subscript>3</Subscript> ceramics

The effects of CuO–Bi₂O₃–V₂O₅ additions on the sintering temperature and the microwave dielectric properties of MgTiO₃ ceramics were investigated systematically. The CuO–Bi₂O₃–V₂O₅ (CuBiV) addition significantly lowered the densification temperature of MgTiO₃ ceramics from 1400 °C to about 900 °C, which is due to the formation of the liquid-phase of BiVO₄ and Cu₃(VO₄)₂ during sintering. The saturated dielectric constant (ε_r) increased, the maximum quality factor (Qf) values decreased and the temperature coefficient of resonant frequency (τ_f) shifted to a negative value with the increasing CuBiV content, which is mainly attributed to the increase of the second phase BiVO₄. MgTiO₃ ceramics with 6 wt.% CuBiV addition sintered at 900 °C for 2 h have the excellent microwave dielectric properties: ε _r= 18.1, Qf = 20300 GHz and τ_f = −57 ppm/ °C.     

Dielectric properties of B<Subscript>2</Subscript>O<Subscript>3</Subscript> doped Sm(Co<Subscript>1/2</Subscript>Ti<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> ceramics at microwave frequency

The microwave dielectric properties and the microstructures of Sm(Co_1/2Ti_1/2)O₃ ceramics with B₂O₃ additions (0.25 and 0.5 wt%) prepared by conventional solid-state route have been investigated. The prepared Sm(Co_1/2Ti_1/2)O₃ exhibited a mixture of Co and Ti showing 1:1 order in the B-site. Doping with B₂O₃ (up to 0.5 wt%) can effectively promote the densification of Sm(Co_1/2Ti_1/2)O₃ ceramics with low sintering temperature. It is found that Sm(Co_1/2Ti_1/2)O₃ ceramics can be sintered at 1,260 °C due to the grain boundary phase effect of B₂O₃ addition. At 1,290 °C, Sm(Co_1/2Ti_1/2)O₃ ceramics with 0.5 wt% B₂O₃ addition possess a dielectric constant (ε _r) of 27.7, a Q × f value of 33,600 (at 9 GHz) and a temperature coefficient of resonant frequency (τ_f) of −11.4 ppm/ °C. The B₂O₃-doped Sm(Co_1/2Ti_1/2)O₃ ceramics can find applications in microwave devices requiring low sintering temperature.     

Properties of neodymium-doped Ca<Subscript>0.15</Subscript>Sr<Subscript>1.85</Subscript>Bi<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>18</Subscript> ferroelectric ceramics

Bismuth-layered compound Ca_0.15Sr_1.85Bi_4−xNd_xTi₅O₁₈ (CSBNT, x = 0–0.25) ferroelectric ceramics samples were prepared by solid-state reaction method. The effects of Nd³⁺ doping on their ferroelectric and dielectric properties were investigated. The remnant polarization Pr of CSBNT ceramics increases at beginning then decreases with increasing of Nd³⁺ doping level, and a maximum Pr value of 9.6 μC/cm² at x = 0.05 was detected with a coercive field Ec = 80.2 kV/cm. Nd³⁺ dopant not only decreases the Curie temperature linearly, but also the dielectric constant (ε_r) and dielectric loss tangent (tan δ). The magnitudes of ε_r and tan δ at the frequency of 100 kHz are estimated to be 164 and 0.0083 at room temperature, respectively.     

Textured BaTi<Subscript>2</Subscript>O<Subscript>5</Subscript> ceramic synthesized by laser rapid solidification method and its dielectric properties

Textured poly crystalline barium dititanate BaTi₂O₅ (BT2) ceramics with a preferred 〈010〉 orientation were synthesized by laser rapid solidification method, with a CO₂ laser. The 〈010〉 orientation of the BT2 is along the laser incident direction, and the orientation factor (f) and relative density of the unannealed BT2 sample are 0.40 and 96.2%, respectively. The two quantities increase with increasing annealing time, and reach the maximum values of 0.42 (annealed at 1,000 °C for 12 h) and 97.5% (annealed at 1,000 °C for 24 h), respectively. The images of scanning electron microscopy reveal that the BT2 are composed of flake-like microstructures with the maximum thickness of 20 μm and dimension of 0.6 mm, which are parallel to the laser incident direction. The measured Curie temperature (T _c) and the maximum dielectric constant (ε_max) are 443 and 6,000 °C, respectively.     

Microstructure and properties of lead-free (Bi<Subscript>1/2</Subscript>Na<Subscript>1/2</Subscript>)TiO<Subscript>3 </Subscript>based piezoelectric ceramics doped with different cations

Different cations doped lead-free piezoelectric (Bi_1/2Na_1/2)TiO₃ ceramics with the general formula Na_0.4995Bi_0.4995Ba_0.001Ti_0.998M_0.002O₃ (M = Nb, Ta, and Sb) were fabricated. The effects of processing parameters and doping on phase content, microstructure, dielectric and piezoelectric properties of the materials were discussed. Experimental results show that Nb doped (Bi_1/2Na_1/2)TiO₃ exhibits superior polarization performance over the existing lead-free ceramics with a d₃₃ value of 122 pC/N obtained when poled at 60 kV/cm at room temperature. The best piezoelectric properties were achieved in (Bi_1/2Na_1/2)TiO₃ doped with Ta having a measured d₃₃ value of 164 pC/N for samples poled at 100 °C under the applied field of 50 kV/cm.