Crystal distortion and electrical properties of Ce-doped BIT-based piezoelectric ceramics

Cerium (Ce)-modified Bi₄Ti_2.94W_0.03Ta_0.03O₁₂ (BITWT) high Curie temperature ceramics (abbreviated as BITWT-xCe) were fabricated by a conventional solid-state sintering method. All BITWT-xCe ceramics had an orthogonal phase, but the structural distortion of the Ce-doped BITWT ceramics was higher than that of BITWT ceramics, which reduced symmetry and improved piezoelectric performance. The relative density (ρ_r) of BITWT-xCe ceramics was greater than 97%. Under the same conditions, the hysteresis loop of BITWT-0.04Ce ceramics had higher saturation than that of BITWT ceramics. The piezoelectric constant (d₃₃) was enhanced, and the highest d₃₃ of 24.7 pC/N at x = 0.04 was obtained, which was 25% higher than that of BITWT ceramics (d₃₃ = 19.8 pC/N). In addition, the tentative conduction mechanism of BITWT-xCe ceramics was also discussed. Two oxidations (Ce³⁺ and Ce⁴⁺) were present in the Ce-doped BITWT ceramics.     

Li0.5Bi2.5Nb2O9: An alkali-metal bismuth layer structured ferroelectric with high TC and small orthorhombic distortion

Bismuth layer structured ferroelectrics (BLSFs) have drawn much attention due to their great potential for high-temperature applications. It is generally accepted that BLSFs with small orthorhombic distortion should have low T_C. In this paper, we report an anomalous example Li_0.5Bi_2.5Nb₂O₉ (LBN), which has small orthorhombic distortion but very high T_C. LBN shows the highest T_C (834°C) among currently reported prototype alkali-metal BLSFs, which is attributed to its small tolerance factor. However, the refinement result reveals that LBN is orthorhombic with the space group of A2₁am, and the orthorhombic distortion of LBN a/b is merely 1.0019. The measurement of piezoelectric coefficient (d₃₃ ∼ 6 pC/N) and observation of striped domain structure confirm the ferroelectricity nature of LBN. This work deepens our understanding of BLSFs and may lead to the finding of more novel BLSFs with high performance.     

A simple Bi3+ self-doping strategy constructing pseudo-tetragonal phase boundary to enhance electrical properties in CaBi2Nb2O9 high-temperature piezoceramics

Calcium bismuth niobate (CaBi₂Nb₂O₉, CBN)-based ceramics are promising candidates for high temperature application, the electrical properties of which are commonly enhanced by complex ion substitution or texture processes. Here, we report that high piezoelectricity and high resistivity were achieved in Ca_1-xBi_2+xNb₂O₉ by constructing pseudo-tetragonal boundary through a simple strategy of Bi³⁺ self-doping. At the pseudo-tetragonal boundary, Ca_0.96Bi_2.04Nb₂O₉ ceramics maintain high Curie temperature T_c = 942 °C, and show high piezoelectric coefficient d₃₃ = 15.1 pC/N and high resistivity ρ_dc = 2 × 10⁶ Ω cm (@600 °C). It is proved that the good piezoelectric property mainly originates from the increase of domain density. In addition, Ca_0.96Bi_2.04Nb₂O₉ ceramics reveal good thermal depoling performance, remaining 90% of piezoelectricity after thermal depoling at 900 ℃, which is due to small thermal expansion and structural distortion. Our work provides a promising candidate for high temperature applications and an easy way to improve the performance of Aurivillius-type piezoelectric ceramics.     

Crystal structure and electrical properties of (Li,Ce, Nd)-multidoped CaBi2Nb2O9 high temperature ceramics

(Li, Ce, and Nd)-multidoped CaBi₂Nb₂O₉ (CBN) Aurivillius phase ceramics were prepared via a conventional solid-state sintering route. The crystal structure including bond lengths and bond angles, microstructure, dielectric constant, DC resistivity, and piezoelectric properties were systematically investigated. Rietveld-refinements of X-ray results indicated that small quantity of (Li, Ce, Nd) doping (< 2.5 mol%) increases orthorhombic distortion, because of the smaller ionic radii of doping ions. However, orthorhombic distortion obviously decreased with increasing (Li, Ce, Nd) doping concentration from 5 to 25 mol%. The replacement of asymmetric A-site Bi³⁺ with 6s2 lone pair electrons by symmetric Li⁺, Ce³⁺ and Nd³⁺ ions decreased the orthorhombic distortion. The morphologies and electrical properties of sintered ceramics were tailored by the introducing (Li, Ce, Nd) multi-dopants. The improvement of piezoelectric properties of modified-CBN ceramics were attributed to decreasing grain sizes and morphotropic phase boundary (MPB). Ca_0.85(Li_0.5Ce_0.25Nd_0.25)_0.15Bi₂Nb₂O₉ (CBNLCN-15) ceramics had optimum properties, and d₃₃ and T_c values were found to be ~ 13.1 pC/N and ~ 900 °C, respectively.     

The structure and electrical properties of Ca0.6(Li0.5Bi0.5-xPrx)0.4Bi2Nb2O9 high-temperature piezoelectric ceramics

Ca_0.6(Li_0.5Bi_0.5-xPr_x)_0.4Bi₂Nb₂O₉ ceramics were prepared via a solid-state reaction method. The effect of the Pr content on the structural and electrical properties was systematically investigated. X-ray diffraction (XRD) combined with Rietveld refinement and X-ray photoelectron spectroscopy (XPS) demonstrated that a moderate amount of Pr³⁺ can be incorporated into the NbO₆ octahedra, while excess Pr³⁺ ions probably enter into the (Bi₂O₂)²⁺ layers, thus resulting in an increase in the tetragonality of the crystal structure. The introduction of Pr suppressed the generation of oxygen vacancies and improved the preferential grain growth along the c-axis, which might be responsible for enhancing the resistivity (ρ ~ 10⁶ Ω cm at 600°C). The replacement of Pr³⁺ for A-site Bi³⁺ enhanced the piezoelectric property, and the piezoelectric constant d₃₃ increased from 13.8 pC/N to 16.3 pC/N. The high depolarization temperature (up to 900°C) implied that CBN-LBP100x ceramics are promising candidates for ultrahigh-temperature application.     

Enhanced electrical properties of Cr2O3 addition NBT-based high-temperature piezoelectric ceramics

Owing to industrial and technological developments, there has been an increasing demand for piezoelectric ceramics that can function at temperatures of 500°C or higher. Na_0.5Bi_4.5Ti₄O₁₅ (NBT) with its high Curie temperature (T_C) of 650°C is a typical bismuth layer–structured ferroelectric. However, its relatively low piezoelectric coefficient (d₃₃ ∼ 16 pC/N) hinders its potential application at high temperatures. In this study, compositions of Ca_0.05(Na_0.5Bi_0.5)_0.95Bi₄Ti₄O₁₅ with different additions of Cr₂O₃ (CNBT–Cr100x) were designed based on previous studies on Ca²⁺-doped NBT piezoceramics, and the effects of the addition on the structural and electrical properties were investigated. The d₃₃ value of CNBT–Cr20 was as high as 29 pC/N, almost twice higher than that of pure NBT ceramics. This increase was investigated in depth using X-ray diffraction refinement and piezoelectric force microscopy in terms of intrinsic and extrinsic contributions. The P_s values of CNBT and CNBT–Cr20 were almost equal. The density of the domain walls of CNBT–Cr20 was significantly higher than that of CNBT, indicating that the increase of d₃₃ of CNBT–Cr20 is mainly due to the increase in the extrinsic contribution. The CNBT–Cr20 ceramic exhibited excellent properties with a high T_C of 655°C, a high d₃₃ of 29 pC/N, and a resistivity high than 10⁶ Ω cm at 500°C, demonstrating its potential for applications at high temperatures such as 500°C.     

Effects of cerium on structures and electrical properties of (Nb,Ta) modified Bi4Ti3O12 piezoelectric ceramics

Bi₄Ti₃O₁₂ high-temperature piezoelectric ceramics composed of 0.03 mol (Nb, Ta)⁵⁺ substituting B site and x mol CeO₂ (x = 0–0.05, abbreviated as BCTNT100x) substituting A site were synthesized by the conventional solid-state reaction method. The effects of Ce additive on the structures and electrical properties of resulting Bi₄Ti₃O₁₂-based ceramics were systematically investigated. In-situ temperature-dependent X-ray diffraction (XRD) confirmed that the phase structure of BCTNT100x ceramics change from orthorhombic structure to tetragonal structure as temperature increased. The ceramics at Ce content x = 0.03 illustrated optimal performances with superior piezoelectric constant (d₃₃ = 36.5 pC/N), high Curie temperature (T_C = 649 °C), and large remanent polarization (2P_r = 21.6 μC/cm²). BCTNT3 ceramics also possessed high d₃₃ of 32.5 pC/N at an annealing temperature of 600°C, with electrical resistivity preserved at 10⁶ Ω cm at 500 °C. These results demonstrate that BCTNT100x ceramics can be used as high-temperature piezoelectric devices.     

Structure and electrical properties of Ce-modified Ca1-xCexBi2Nb1.75(Cu0.25W0.75)0.25O9 high Curie point piezoelectric ceramics

Ca_1-xCe_xBi₂Nb_1.975(Cu_0.25W_0.75)_0.025O₉ (CBNCW-xCe: x = 0.00, 0.02, 0.04, 0.06, and 0.09) lead-free piezoelectric ceramics with improved piezoelectric properties were prepared by the traditional solid-state reaction method. The effects of CeO₂ doping on the microstructure and electrical properties were investigated in detail. XRD patterns and Rietveld refinement show that the crystal structures of the samples transform from the orthorhombic phase into the pseudotetragonal phase and that the lattice distortion is weakened. Raman and XPS spectra indicate that Ce ions exist with +3 and + 4 valences in the air sintered ceramics, in which Ce⁴⁺ replaces Nb⁵⁺, causing the weakened NbO₆ octahedral vibration of torsional and tensile and an increase in oxygen vacancies in the doped ceramics. When x = 0.04, it shows excellent comprehensive properties with a high d₃₃ value of 18.1 pC/N, a T_c value of 900 °C, and a ρ_dc value of 2.8 × 10⁵ Ω cm at 500 °C. Our results suggest that the CBNCW-0.04Ce ceramic is a promising candidate in high-temperature piezoelectric applications.     

Piezoelectric and dielectric properties of Bi0 ˙ 5(Na0 ˙ 84K0 ˙ 16)0 ˙ 5TiO3–Ba(Zr0 ˙ 04Ti0 ˙ 96)O3 lead free piezoelectric ceramics

Abstract

Lead free piezoelectric ceramics (1–x)Bi_0˙5 (Na_0˙84K_0˙16)_0˙5TiO₃–xBa(Zr_0˙04Ti_0˙96)O₃ (BNKT–BZT100x, wherein x ranged from 0 to 10 mol.-%) were fabricated by a conventional mixed oxide route, whose BZT content effect on electrical properties and crystalline structures was investigated. X-ray diffraction investigation showed that BZT effectively diffused into BNKT lattice and formed a solid solution during sintering, and their crystalline structures changed from rhombohedral phase to tetragonal phase as the BZT content was increased. Piezoelectric property measurements revealed that the BNKT–BZT4 ceramics had the highest piezoelectric performance: piezoelectric constant d ₃₃ reached 178 pC N^–1 and planar electromechanical coupling factor k _p was up to 0˙33. The influence of Bi₂O₃ doped content on electrical properties and crystalline structure of the BNKT–BZT4 ceramics were also studied, and found that the piezoelectric property of the ceramics was enhanced when Bi₂O₃ was doped.     

Ca2+ doping effects on the structural and electrical properties of Na0.5Bi4.5Ti4O15 piezoceramics

Bismuth layer structured Na_0.5Bi_4.5Ti₄O₁₅ (NBT) ferroelectric is one of the most promising materials for potential applications at high temperature. However, it is challenged to achieve a balance between high Curie temperature piezoelectric coefficient and excellent thermal stability for NBT piezoceramics. Here, through chemical modification at the A site of NBT with Ca²⁺, novel (Na_0.5Bi_0.5)_1-xCa_xBi₄Ti₄O₁₅ piezoceramics with excellent properties fabricated by solid state reaction were studied. After doping of Ca²⁺, the Curie temperature T_C increased from 648 °C to 662 °C while the piezoelectric coefficient d₃₃ increased from 14 pC/N to 22 pC/N which can be attributed to the intrinsic contribution of TiO₆ octahedral lattice distortion (tilting and rotation) and the extrinsic contribution of the increased density of domain walls. The composition of (Na_0.5Bi_0.5)_0.95Ca_0.05Bi₄Ti₄O₁₅ ceramics with x = 0.05 has the optimal performance with high T_C of 655 °C, large d₃₃ of 22 pC/N, high electrical resistivity ρ close to 10⁷ Ω cm at 500 °C and especially excellent thermal stability of d₃₃ only about 5% reduction after being annealed at 625 °C. The work effectively reveals the great potential of CNBT-5 ceramics for high-temperature piezoelectric applications.     

Comparison of multi-valent manganese oxides (Mn4+, Mn3+, and Mn2+) doping in BiFeO3-BaTiO3 piezoelectric ceramics

Different manganese oxides-doping effects were compared in piezoceramic BiFeO₃-BaTiO₃ system. 0.67Bi_1.05(Fe_0.99Mn^x_0.01)O₃-0.33BaTiO₃ (valence state x = 4+, 3+, and 2+) ceramics were prepared via a solid-state reaction process followed by furnace-cooling (FC) or water-quenching (WQ) process. For the FC ceramics, the direct piezoelectric sensor coefficient (d₃₃) was almost independent of valence state of doped Mn, while d₃₃ depended on the fraction of Fe³⁺/Fe²⁺ in WQ ceramics. The d₃₃ value was highest for the donor Mn⁴⁺-doped ceramic, among the FC ceramics, with 175 pC/N. However, acceptor-doping with Mn²⁺ prevented the transition of Fe ion valence state from 3+ to 2+ in the WQ ceramics, the Mn²⁺-doped WQ ceramic showed the largest d₃₃ of 313 pC/N and converse piezoelectric actuator coefficient, d₃₃^* of 352 pm/V, with high Curie phase transition temperature (482 °C).     

Ternary doping of Na+, Bi3+ and La3+ to improve piezoelectric constant and electrical resistivity simultaneously in calcium bismuth niobate ceramics

High Curie-temperature layer-structured calcium bismuth niobate (CaBi₂Nb₂O₉) piezoelectric ceramics are promising for important application in high-temperature vibration sensors. However, such application is currently limited due to not only poor high-temperature piezoelectric constant (d₃₃), which is attributable to spontaneous polarization along a-b plane and high coercive fields, but also inferior high-temperature electrical resistivity, which results from volatilization of Bi₂O₃ during the sintering process that increases defect concentration of oxygen vacancies. Herein, we report a Na⁺, Bi³⁺ and La³⁺ ternary-doping-strategy to obtain Ca_0.8(Na_0.5La_0.3Bi_0.2)_0.2Bi₂Nb₂O₉ ceramics, which exhibited higher piezoelectric constant and larger electrical resistivity as accompanied by a better thermal stability at high-temperatures. The piezoelectric constant was enhanced from 8.8 pC/N in pristine CaBi₂Nb₂O₉ to 13.4 pC/N in Ca_0.8(Na_0.5La_0.3Bi_0.2)_0.2Bi₂Nb₂O₉ ceramics, which is ascribed to the presence of pseudo-tetragonal structural distortion after La³⁺ doping. In addition, the electrical resistivity at 600 °C was increased by more than one-order of magnitude from 3.7 × 10⁴ Ω cm in pristine CaBi₂Nb₂O₉ to 1.4 × 10⁶ Ω cm in Ca_0.8(Na_0.5La_0.3Bi_0.2)_0.2Bi₂Nb₂O₉ ceramics. Such significant improvement in electrical resistivity results from the reduction in oxygen vacancies due to ternary doping of Na⁺, Bi³⁺ and La³⁺ and stronger binding interaction between La³⁺ dopants and O^2? in (Bi₂O₂)²⁺ layers in Ca_0.8(Na_0.5La_0.3Bi_0.2)_0.2Bi₂Nb₂O₉ ceramics. This work demonstrates an important way of employing chemical doping to improve piezoelectric constant and electrical resistivity simultaneously at high-temperatures to tune structural distortion in bismuth-layered structural CaBi₂Nb₂O₉ ceramics.     

Enhanced electrical properties in W/Cu co-doped CaBi2Nb2O9 high-temperature piezoelectric ceramics

CaBi₂Nb₂O₉ (CBN)-based high-temperature piezoelectric ceramics with the formula of CaBi₂Nb_2−x(W_3/4Cu_1/4)_xO₉ were prepared via the traditional solid-state reaction method. Both the bulk microstructure and the electrical performance of the W/Cu co-doped CBN-based ceramics were systematically investigated. The results indicated that the W/Cu incorporation into the Nb-site altered the crystal structure, which enhanced the piezoelectricity and resistivity. The ceramic with the composition CaBi₂Nb_1.96(W_3/4Cu_1/4)_0.04O₉ exhibited good performance with a high d₃₃ (~14 pC/N) and T_C (~939℃). Moreover, the ceramic exhibited a good electrical resistivity (ρ) of 4.91 × 10⁵ Ω·cm and a low dielectric loss (tanδ) of 0.1 at 600℃. Furthermore, the ceramic that was annealed at 900℃ for 2 h presented a d₃₃ value of 13 pC/N, thus indicating good thermal stability of the piezoelectric properties. All these results confirm that the CaBi₂Nb_1.96(W_3/4Cu_1/4)_0.04O₉ ceramic may act as a potential promising candidate for piezoelectric device applications in high-temperature environments.     

Enhanced thermal stability of (NaCe)‐multidoped CaBi2Nb2O9 by A‐site vacancies‐induced pseudo‐tetragonal distortion

Although A‐site codoping of alkali metal and rare‐earth elements are known to effectively promote the d₃₃ of CaBi₂Nb₂O₉ (CBN), its thermal depoling behavior cannot be well promised. In this work, piezoelectricity of CBN was effectively promoted by (NaCe) modification, and its thermal instability was caused by the lattice evolution from orthorhombic structure to pseudo‐tetragonal structure during thermal depoling process. A‐site vacancies could induce pseudo‐tetragonal distortion in Ca_0.92(Na_0.5Ce_0.5)_0.08Bi₂Nb₂O₉ ceramic, which obviously enhanced the thermal stability of lattice by reducing the rotation of the Nb–O octahedron during the thermal depoling process, as compared with orthorhombic structure, thereby weakening the swing of spontaneous polarization (P_s) and promoting the thermal depoling performance. Consequently, good thermal stability was obtained (remained 92% of initial d₃₃ after depoling at 600°C). Moreover, dominant role of oxygen vacancies in the electrical conduction and relaxation process promised that the introduction of small amount of A‐site vacancies would not influence the electrical properties obviously.     

Structural,dielectric, and piezoelectric properties of Ce-doped Bi7Ti4.2Ta0.3W0.5O21 intergrowth ferroelectric ceramics

The Bi_7-xCe_xTi_4.2Ta_0.3W_0.5O₂₁ (BTTW-BITT-xCe, x = 0.05, 0.10, 0.15, 0.20) ceramics were studied as potential materials for high-temperature applications. The microstructure, dielectric, piezoelectric and ferroelectric properties of Ce doped BTTW-BITT samples were analyzed in detail. The results indicated that an appropriate amount of Ce ion doping could inhibit the growth of grains, suppress the relaxation peak, reduce high-temperature dielectric losses, and greatly improve the piezoelectric activities. The optimal ceramics was obtained at x = 0.15, which possessed a maximum piezoelectric constant of d₃₃ = 23.4 pC/N, a high Curie temperature of 713 °C, a loss value of 6% at 500 °C, and a favorable thermal stability of d₃₃ = 21.1 pC/N (90% of the initial value) at 500 °C. This result indicates that BTTW-BITT-0.15Ce has great potential for applications in the high temperature fields. In addition, XPS results showed that there were two Ce valences states, Ce³⁺ and Ce⁴⁺present in the BTTW-BITT-xCe ceramics.     

Enhanced piezoelectric properties and temperature stability of Bi4Ti3O12-based Aurivillius ceramics via W/Nb substitution

Bi₄Ti₃O₁₂ (BIT), a typical Aurivillius ceramics with high Curie temperature (T_c ? 675 °C), has great potential for high temperature applications. This work provides an effective method of inducing structure distortion, relieving the tetragonal strain of the TiO₆ octahedron and decreasing the concentration of oxygen vacancies to improve the piezoelectricity and temperature stability of BIT ceramics. Bi₄Ti_2.98W_0.01Nb_0.01O₁₂ possesses an optimum piezoelectric coefficient (d₃₃) of 32 pC/N, a high T_c of 655 °C and a large resistivity of 3 × 10⁶ Ω·cm at 500 °C. The maximum d₃₃ reported here is approximately quadruple than that of pure BIT (?7 pC/N). Moreover, the d₃₃ of W/Nb co-doped BIT and the in-situ temperature stability of the compression-mode sensor present a highly stable characteristic in the range of 25–600 °C. These results imply that W/Nb-modified BIT ceramics is a promising candidate for application at high temperatures of up to 600 °C.     

Performance enhancement of soft-PZT5 piezoelectric ceramics using poling technique

Pb(Zr_1−xTi_x)O₃ (PZT) ceramics are the most widely used piezoelectric ceramics due to their excellent performance. It has been reported that the direct current poling (DCP) apply on alternating current poling (ACP) relaxor-PbTiO₃ ferroelectric crystals can further improve the piezoelectric properties. Herein, we report the dielectric and piezoelectric properties of soft-PZT5 ceramics under DCP, ACP, and ACP + DCP methods. The piezoelectric coefficient d₃₃ of the soft-PZT5 ceramics was 560 pC/N using ACP+DCP at room temperature (RT), which is 4% higher than the ACP-treated sample (540 pC/N) and 24% higher than the DCP-treated sample (450 pC/N). The ideal poling temperatures of DCP and ACP were found to be 120°C and 60°C, showing optimal d₃₃ values of 540 pC/N and 565 pC/N, respectively. The ACP and ACP+DCP samples show the same aging trend. After 30 days of aging, the d₃₃ values of the DCP, ACP, and ACP+DCP soft-PZT5 ceramics were 415 pC/N, 500 pC/N, and 510 pC/N, respectively, showing decreases of 12%, 8%, and 9%, respectively. This work indicates that the ACP+DCP method is an effective method to improve the piezoelectric properties of soft-PZT5 ceramics.     

Achieving both large transduction coefficient and high Curie temperature of Bi and Fe co-doped PZT piezoelectric ceramics

Achieving both the large transduction coefficient (the product of piezoelectric charge d₃₃ and voltage coefficients g₃₃) and high Curie temperature is very important to improve the power generation performance and their thermal stability of piezoelectric energy harvesters. It is difficult to improve the transduction coefficient of the commercial PZT based piezoelectric ceramics due to the same variation trend of piezoelectric charge coefficient and dielectric constant with chemical modifications. In this work, Bi₂O₃ and Fe₂O₃ co-modified ((Pb_1-xBi_x)((Zr_0.53Ti_0.47)_1-xFe_x)O₃) ceramics were prepared by conventional solid state reaction method, and their dielectric and piezoelectric properties were studied. The piezoelectric charge coefficient d₃₃ increases by Bi and Fe co-modifications due to the enlarged grain size and reduced lattice distortion, while the dielectric constant ε₃₃ deceases mainly owing to the increased micro-pores in grains, leading to the enhancement transduction coefficient d₃₃×g₃₃. The Curie temperature Tc and maximum transduction coefficient d₃₃×g₃₃ are 346 °C and 17169 × 10^?15 m²/N, respectively, which are both higher than those of commercial PZT and PZN-PZT based piezoelectric ceramics. This work provides a new way to enhance the transduction coefficient of PZT based ceramics for piezoelectric energy harvesters used in wide temperature range.     

Enhanced piezoelectric properties of Aurivillius-type sodium lanthanum bismuth titanate (Na0.5La0.5Bi4Ti4O15) by B-site manganese modification

The Aurivillius-type bismuth layer-structured ferroelectrics (BLSFs) sodium lanthanum bismuth titanate (Na_0.5La_0.5Bi₄Ti₄O₁₅, NLBT) polycrystalline ceramics with 0.0–0.4 wt% MnO₂ were synthesized using conventional solid-state processing. Phase analyses were performed by X-ray powder diffraction (XRPD), and the microstructural morphology was assessed by scanning electron microscopy (SEM). The dielectric and piezoelectric properties of the manganese-modified NLBT ceramics were investigated in detail. The results show that manganese is very effective in promoting the piezoelectric activities of NLBT ceramics, and the reasons for piezoelectric activities enhancement by manganese modification are explained. The NLBT ceramics modified with 0.2 wt% MnO₂ (NLBT-Mn2) possess good piezoelectric properties, with a piezoelectric coefficient d₃₃ of 28 pC/N. This value is the highest value among the modified NLBT-based piezoelectric ceramics examined. The temperature-dependent dielectric spectra show that the Curie temperature T_c of the manganese-modified NLBT ceramics is slightly higher than that of the pure NLBT ceramics. Thermal annealing analysis revealed that the manganese-modified NLBT ceramics possess good thermal stabilities up to 500 °C. These results demonstrate that the manganese-modified NLBT ceramics are promising materials for high temperature piezoelectric applications.     

Enhancement of piezoelectric properties of BF–BT ceramics by using ZrO2 powder bed during the sintering process

ZrO₂ powders of various particle sizes (0.15, 0.7, 500 µm) were used to simulate loose powder bed sintering to prepare BF–BT piezoelectric ceramics. The phase structure, dielectric properties, ferroelectric properties, and piezoelectric properties were compared with the samples sintered by the conventional powder bed method (i.e., powder of the same composition as the sample). Results showed that the use of loose ZrO₂ powder bed could improve the heat conduction rate and the sintering quality of bulk BF–BT piezoelectric ceramics. The XPS results showed that the samples sintered with 500 µm ZrO₂ powder beds had the lowest concentration of Fe²⁺, exhibited the largest piezoelectric coefficients (d₃₃ = 201 pC/N). In contrast, the sample sintered with a conventional powder bed under the same sintering conditions had a piezoelectric coefficient d₃₃ of 156 pC/N.