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.     

Enhanced piezoelectric activity with good thermal stability and improved electrical resistivity in Ta–Mn co-doped CaBi4Ti4O15 high-temperature piezoceramics

Aurivillius phase CaBi₄Ti_4-x (Ta_2/3Mn_1/3)_xO₁₅ (x = 0–0.1) high-temperature piezoelectric ceramics were fabricated using the conventional solid-state reaction process. The effects of the Ta–Mn co-doping level on the structure, piezoelectric properties and electrical conduction behaviours of the as-prepared CBT (CaBi₄Ti₄O₁₅) ceramics were explored in detail. It was revealed that the Ta–Mn co-doping efficaciously enhanced the electrical performances of the CaBi₄Ti₄O₁₅ ceramic, which may be due to optimisation of the crystal structure and a reduction in the oxygen vacancy concentration. The composition with x = 0.04 presented superior electrical properties with an outstanding piezoelectric constant (d₃₃) of 24 pC/N accompanied by a high Curie temperature (T_C) of 793 °C, an optimised dielectric loss (tanδ) of 1.5%, and an improved resistivity (ρ) of 4.96 × 10⁸ Ω cm at 400 °C. Moreover, the ceramic exhibited impressive thermal stability with the d₃₃ value maintaining 91.7% of its initial value at room temperature (25 °C) after being annealed at 600 °C for 2 h. The improved performance indicates that the Ta–Mn co-doped CaBi₄Ti₄O₁₅ ceramic might be a promising candidate for piezoelectric device applications at elevated temperatures.     

Doping level effects in Nb self-doped Bi3TiNbO9 high-temperature piezoceramics with improved electrical properties

Nb self-doped Bi₃Ti_1-xNb_1+xO₉ (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1) high-temperature piezoelectric ceramics were fabricated through the conventional solid-state sintering method. The effects of different Nb self-doping levels on the microstructure, piezoelectric activities, and electrical conduction behaviors of these Nb self-doped Bi₃Ti_1-xNb_1+xO₉ ceramics were studied in detail. Large doping level effects on piezoelectric activity and resistivity were confirmed, which might be ascribed to the evolution of the crystal structure and the variations of the oxygen vacancy concentration and the grain anisotropy induced by Nb doping. An optimized piezoelectric coefficient (d₃₃) of 11.6 pC/N was achieved at x = 0.04 with a Curie temperature of 906°C. Additionally, an improved DC resistivity of 6.18 × 10⁵ Ω·cm at 600°C was acquired in this ceramic. Furthermore, the ceramic exhibited excellent thermal stability with the d₃₃ value maintaining 95% of its initial value after being annealed at 850°C for 2 hours. These results showed that Nb self-doped Bi₃Ti_1-xNb_1+xO₉ ceramics might have great potentials for high-temperature piezoelectric applications.     

Enhancing giant dielectric properties of Ta5+-doped Na1/2Y1/2Cu3Ti4O12 ceramics by engineering grain and grain boundary

Various strategies to improve the dielectric properties of ACu₃Ti₄O₁₂ (A = Sr, Ca, Ba, Cd, and Na_1/2Bi_1/2) ceramics have widely been investigated. However, the reduction in the loss tangent (tanδ) is usually accompanied by the decreased dielectric permittivity (ε′), or vice versa. Herein, we report a route to considerably increase ε′ with a simultaneous reduction in tanδ in Ta⁵⁺–doped Na_1/2Y_1/2Cu₃Ti₄O₁₂ (NYCTO) ceramics. Dense microstructures with segregation of Cu– and Ta–rich phases along the grain boundaries (GBs) and slightly increased mean grain size were observed. The samples prepared via solid-state reaction displayed an increase in ε′ by more than a factor of 3, whereas tanδ was significantly reduced by an order of magnitude. The GB–conduction activation energy and resistance raised due to the segregation of Cu/Ta–rich phases along the GBs, resulting in a decreased tanδ. Concurrently, the grain–conduction activation energy and grain resistance of the NYCTO ceramics were reduced by Ta⁵⁺ doping ions owing to the increased Cu⁺/Cu²⁺, Cu³⁺/Cu²⁺, and Ti³⁺/Ti⁴⁺ ratios, resulting in enhanced interfacial polarization and ε′. The effects of Ta⁵⁺ dopant on the giant dielectric response and electrical properties of the grain and GBs were described based on the Maxwell–Wagner polarization at the insulating GB interface, following the internal barrier layer capacitor model.     

Piezoelectricity,thermal stability,and fatigue resistance in Nb and Ta-doped Bi4Ti3O12 high-temperature piezoceramics

The effect of Nb/Ta donor doping on the piezoelectricity, thermal stability, and fatigue resistance of bismuth titanate Bi₄Ti₃O₁₂ (BIT) ceramics was investigated in relation to their structural and oxygen vacancy-related electrical properties. As the Nb/Ta doping amount increased, the activation energy of oxygen vacancy conduction increased, indicating a reduction in the concentration of oxygen vacancies. The improved electrical insulating properties of the Nb/Ta-doped Bi₄Ti₃O₁₂ ceramics (BTNT) with fewer oxygen vacancies, contributed to their effective poling and strong piezoelectricity. Outstanding piezoelectric performance with high piezoelectric constant (39 pC/N) and Curie temperature (690 °C) could be achieved in the 0.005 mol Nb/Ta-doped BTNT ceramic with high density and anisotropic grain growth. The BTNT ceramics exhibited superior thermal aging stability and fatigue resistance compared to the BIT ceramic, suggesting that the reduction of oxygen vacancy defects plays a decisive role in enhancing elevated-temperature-induced and electric-field-induced degradation stabilities.     

BNT-based ferroelectric ceramics: Electrical properties modification by Ta2O5 oxide addition

Due to their superior piezo-responses (strain S > 0.3%), bismuth sodium titanate (BNT)-based relaxor ferroelectrics have received much attention. Compared to other chemical elements, tantalum (Ta) doping provides superior electro-strain for these ferroelectrics, while the effect of Ta₂O₅ as oxide additive has been rarely reported. Herein, lead-free piezoceramics of Bi_0.5(Na_0.72K_0.22Li_0.06)_0.5TiO₃-xTa₂O₅ (BNKLT-xTa₂O₅, x = 0-0.015) are synthesized. We study the effects of Ta₂O₅ addition on the crystal structure, piezoelectric responses, dielectric properties, and ferroelectric properties of BNKLT ceramics. All of the ceramics exhibit a typical perovskite structure, and Ta₂O₅ diffuses into the BNKLT lattice to form a uniform solid solution. The addition of Ta₂O₅ can make the grains more regular and uniform, while excess Ta₂O₅ result in finer grains. The undoped BNKLT ceramics show good ferroelectric and piezoelectric properties (remnant polarization P_r = 22.5 μC/cm² and piezoelectric coefficient d₃₃ = 250 pC/N); however, the addition of Ta₂O₅ leads to an clear degradation in d₃₃ and P_r. Meanwhile, the addition of an appropriate Ta₂O₅ amount leads to an increase in the electro-strain, and the unipolar strain reaches 0.385% under 60 kV/cm for x = 0.003, together with a higher normalized strain (d₃₃^*=S_max/E_max) of 633 pm/V (x = 0.003). The enhanced strain behaviors can be attributed to the coexistence of the ferroelectric and relaxor states, and an excellent electrostriction coefficient Q₃₃ (Q₃₃ = S/P²) value of 0.038 m⁴C⁻² is obtained under 60 kV/cm for x = 0.003.     

Remarkable piezoelectric activity and high electrical resistivity in Cu/Nb co-doped Bi4Ti3O12 high temperature piezoelectric ceramics

Cu/Nb co-doped Aurivillius type Bi₄Ti_3-x(Cu_1/3Nb_2/3)_xO₁₂ (BTCN) ceramics were investigated as a potential candidate for high temperature piezoelectric application. The microstructure, phase structure and resulting piezoelectric properties and conduction behaviors were systematically investigated. A remarkable d₃₃ of 38 pC/N was achieved in the ceramic with a composition of x = 0.015, which may be ascribed to the enhancement of remanent polarization and decrease of coercive field. Moreover, a high DC resistivity of 8.39 × 10⁶ Ω·cm at 500 °C was also obtained in the composition, due to the decrease of the oxygen vacancy concentration induced by the doped Cu/Nb. Furthermore, the ceramic also exhibited stable thermal annealing behaviors and excellent fatigue resistance. All the results demonstrated the great potential of the Cu/Nb co-doped Bi₄Ti₃O₁₂ ceramics for high temperature piezoelectric applications.     

Influence of Ti4+ substitution for Ta5+ on the crystal structure,Raman spectra,and microwave dielectric properties of Ba3Ta4-4xTi4+5xO21 ceramics

This paper systematically investigated the influence of Ti⁴⁺ substitution for Ta⁵⁺ on the phase composition and microwave dielectric properties of Ba₃Ta_4-4xTi_4+5xO₂₁ (x = 0.1, 0.2, and 0.3) ceramics with hexagonal tungsten bronze-like structures. X-ray diffraction and Rietveld refinement results indicated that single-phase Ba₃Ta₄Ti₄O₂₁ could be obtained only with the x values of 0.1 and 0.2, and a secondary phase was detected at an x value of 0.3. The valence state of Ba₃Ta_4-4xTi_4+5xO₂₁ (x = 0.2) ceramics was analyzed through X-ray photoelectron spectroscopy. Increasing Ti⁴⁺/Ta⁵⁺ ratios could reduce sintering temperature and improve the microwave dielectric properties of Ba₃Ta_4-4xTi_4+5xO₂₁ solid solutions. However, the dielectric properties, particularly the quality factor, of Ba₃Ta_4-4xTi_4+5xO₂₁ ceramics deteriorated severely as a result of oxygen vacancy defects caused by the transition of the valence state from Ti⁴⁺ to Ti³⁺ when x = 0.2 and the coexistence of the secondary phase when x = 0.3. Infrared reflectivity spectroscopy was performed to explore the intrinsic dielectric properties of Ba₃Ta_4-4xTi_4+5xO₂₁ (x = 0.1) ceramics. The measured and extrapolated microwave dielectric properties of Ba₃Ta_4-4xTi_4+5xO₂₁ (x = 0.1) ceramics sintered at 1240 °C for 6 h were ε_r ~ 46.5, Q × f = 13,900 GHz, τ_f ~ +49.4 ppm/°C, and ε_r ~ 44, Q × f = 34,850 GHz.     

Influence of Sb-doping on dielectric properties of NaCu3Ti3TaO12 ceramics and relevant mechanism(s)

A series of NaCu₃Ti₃Ta_1−xSb_xO₁₂ ceramics were prepared by the conventional solid-state reaction technique, and their dielectric properties, crystalline structures, microstructures and complex impedance were investigated systematically. All the ceramics show the main phases of perovskite-related crystallographic structure, and their dielectric properties change significantly with the increasing Sb-doping. All these ceramics exhibit giant dielectric-permittivity properties, and impedance spectroscopy analysis reveals that NaCu₃Ti₃Ta_1−xSb_xO₁₂ ceramics are electrically heterogeneous and composed of insulating grain boundaries and semiconducting grains. Moreover, CuO secondary phase and Cu²⁺/Cu¹⁺, Ti⁴⁺/Ti³⁺, Sb⁵⁺/Sb³⁺ and Ta⁵⁺/Ta³⁺ aliovalences are found to exist in NaCu₃Ti₃Ta_1−xSb_xO₁₂ ceramics through XRD, EDS and XPS analysis. Therefore, CuO segregation and aliovalences of metal ions were suggested to contribute greatly to the internal barrier layer capacitance effect formation in NaCu₃Ti₃Ta_1−xSb_xO₁₂ ceramics. Furthermore, Sb-doping could decrease the tanδ of NaCu₃Ti₃Ta_1−xSb_xO₁₂ ceramics at low frequencies, and the reason was discussed.     

Enhanced piezoelectric performance in Na0.5Bi4.5Ti4O15-based bismuth-layered ceramics by Nb/Mn doping modification

In this work, Na_0.5Bi_4.5Ti_3.94–xMn_0.06Nb_xO_15+y bismuth-layered ferroelectric ceramics were prepared by a solid-state reaction method. The effect of Nb⁵⁺ content on crystal morphology, electrical properties, and piezoelectric performance were systematically investigated. The results show that the introduction of Nb⁵⁺ into Na_0.5Bi_4.5Ti_3.94–xMn_0.06Nb_xO_15+y ceramics to replace Ti⁴⁺ increases the ratio of b/a lattice parameter, leading to the TiO₆ octahedral distortion and the structural transformation tendency from the orthorhombic to tetragonal phase, which facilitates dipole movements of Na_0.5Bi_4.5Ti_3.94–xMn_0.06Nb_xO_15+y ceramics. Therefore, the ferroelectric properties of Na_0.5Bi_4.5Ti_3.94–xMn_0.06Nb_xO_15+y ceramics are improved, and an enhanced piezoelectric coefficient of 30 pC/N combining great temperature stability with d₃₃ value higher than 25 pC/N in the temperature range of 25°C–450°C has been realized in Na_0.5Bi_4.5Ti_3.94–xMn_0.06Nb_xO_15+y ceramics with x = 0.08 mol. Our work provides a good model for designing lead-free ultrahigh Curie temperature piezoelectric devices that can be practically applied in extremely harsh environments.     

Middle-low temperature sintering and piezoelectric properties of CuO and Bi2O3 doped PMS-PZT based ceramics for ultrasonic motors

A ternary solid-solution piezoelectric ceramic of rare-earth oxides modified 0.03 Pb(Mn_1/3Sb_2/3)O₃-0.97 Pb(Zr_0.505Ti_0.495)O₃ + x wt.% CuO + y wt.% Bi₂O₃ (PMS-PZT + x wt.% CuO + y wt. % Bi₂O₃) (x, y = 0–0.2) was successfully prepared via a transient-liquid-phase sintering. Both Cu²⁺ and Bi³⁺ were believed to replace the A-site Pb ions and to evidently induce the lattice shrinkage and the distortion decrease. However, the addition of only a small amount of CuO was found to effectively reduce the sintering temperature, sustain good piezoelectric properties and predominant transgranular fracture modes, but obviously increase the average grain size and high-field dielectric loss. Further experimental results indicate that the grain growth of the ceramics was inhibited effectively and the high-field dielectric loss was reduced through CuO and Bi₂O₃ co-doping. The 0.05 wt% CuO and 0.15 wt% Bi₂O₃ co-doped PMS-PZT ceramics sintered at 1050 °C exhibit excellent dielectric and piezoelectric properties of d₃₃ = 410 pC/N, k_p = 0.62, Q_m = 1478, ε_r = 1550, tan δ = 0.8% (400 V/mm) and T_c = 330 °C. The experimental results can provide a solid fundament for multilayer piezoelectric actuating devices.     

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.     

Comprehensive properties and thermal stability of Ta2O5-doped PIN-PHT ceramics

Herein, high-performance 0.11 Pb(In_1/2Nb_1/2)O₃-0.89 Pb(Hf_0.47Ti_0.53)O₃-0.8Ta₂O₅ (PIN-PHT-0.8Ta) ceramics are successfully synthesized. In addition, performance improvement is comprehensively analyzed from viewpoints of microstructure, phase structure and electrical properties. Experimental results reveal that the addition of Ta₂O₅ changes phase structure of PIN-PHT ceramics from ferroelectric tetragonal phase to rhombohedral phase. This leads to the appearance of morphotropic phase boundaries (MPBs). At the same time, the addition of Ta₂O₅ reduces grain size and enhances grain uniformity. Also, Ta₂O₅ doping improves internal and external contribution of piezoelectric response, which greatly improves dielectric, piezoelectric and ferroelectric properties of PIN-PHT. Key performance parameters include d₃₃, k_p, T_C, ε_r and tanδ, which are found to be 630 pC/N, 0.73, 322.6 °C, 1917 and 1.55%, respectively. In particular, thermal stability of PIN-PHT-0.8Ta ceramics is found to be higher than PZT-based ceramics, as well as d₃₃ value and performance retention rate of PIN-PHT-0.8Ta are found to be 560 pC/N and 89% at 300 °C, respectively, which are far superior to commercial PZT-5 and PZT-8 ceramics. These properties indicate potential of PIN-PHT-0.8Ta ceramics in high-temperature applications.     

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.     

Effects of Mn-Doping on the Properties of BaBi4Ti4O15 Bismuth Layer Structured Ceramics

Bismuth-layer-structured (Ba_1−x Mn _x )Bi₄Ti₄O₁₅ (0.0 ≤ x ≤ 0.8) ceramics were prepared by a Sol–Gel method. The effects of the amount of Mn-doped on the phase structure, the dielectric as well as piezoelectric properties of BaBi₄Ti₄O₁₅ ceramics were studied. The X-ray diffraction results revealed that the introduction of Mn resulting in distortion of lattice, which contributes to the crystallization of the layered structure grains. The densification, dielectric and piezoelectric properties of the (Ba_1−x Mn _x )Bi₄Ti₄O₁₅ ceramics were significantly promoted by the Mn substitution of Ba. When the value of doping amount Mn is 0.4, the (Ba_0.6Mn_0.4)Bi₄Ti₄O₁₅ ceramic exhibited a high piezoelectric constant (d ₃₃ = 7.5 pC/N), a big relatively dielectric constant (ε _r  = 764.26) and a small dielectric loss (tanδ = 0.0124).     

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.     

Dielectric and ferroelectric properties of Ta-modified Bi3.25La0.75Ti3O12 ceramics

B-site modified Bi_3.25La_0.75Ti_3-xTa_xO₁₂ ceramics were prepared by the conventional solid-state reaction method. The influence of Ta₂O₅ on microstructure and electric properties of the ceramics was investigated. The results demonstrated that Ta⁵⁺ ions were dissolved into the perovskite lattice and homogeneously distributed in the matrix without forming any minority phase. The conduction mechanism and dielectric response behavior were transformed with Ta substation, which is triggered by varied structural distortion characteristics and defect diploes. The Curie temperature decreased gradually with increasing Ta content and a relaxor-like behavior was observed for x = 0.09 sample. The internal bias field is decreased with Ta doping, because the substitution of Ta⁵⁺ at B-site contributes to release the involved oxygen vacancies in defect diploes. Moreover, further increasing Ta content causes a reduction in the oxygen vacancies located at lattice misfits, resulting in a decrease of coercive fields. An improved ferroelectric properties were obtained for x = 0.09 sample with a relatively lower coercive field and a larger spontaneous polarization.     

The large electro-strain in BNKT-BST-100xTa lead-free ceramics

0.94Bi_0.5(Na_0.78K_0.22)_0.5Ti_1-xTa_xO₃-0.06Ba_0.95Sr_0.05TiO₃ (BNKT-BST-100xTa, for x = 0,0.005, 0.010, 0.015, 0.020 and 0.025) lead-free ceramics were fabricated by the solid-state reaction technique. Microstructure, dielectric, ferroelectric and fatigue performances of BNKT-BST-100xTa ceramics had been systemically studied. The XRD patterns confirmed that Ta⁵⁺ ions had completely dissolved into the lattice of BNKT-BST-100xTa ceramics. Meanwhile, the temperature of R3c-PNRs (T_s) was found to shift towards room temperature in dielectric permittivity curves with the introduction of Ta⁵⁺ ions. In addition, the highest unipolar strain of 0.32% with the corresponding normalized strain of 458 pm/V was obtained for x = 0.020 under the applied electric field of 70 kV/cm. The large electro-strain was cause by intrinsic effect of the crystal and the external electric field. Moreover, the excellent strain fatigue resistance indicated the prepared ceramics are promising candidates for actuators and stress sensors.     

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.     

Structural and electric properties of Ce-doped Na0.5Bi4.5Ti4O15 piezoceramics with high Curie temperatures

Na_0.5Bi_4.5-xCe_xTi₄O₁₅ (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) lead-free piezoelectric ceramics with high Curie temperatures are fabricated using the conventional solid-phase method. The effects of the Ce content on the phase structures, morphologies, and electrical properties of the Na_0.5Bi_4.5-xCe_xTi₄O₁₅ ceramics are systematically investigated. The appropriate content of Ce increases b/a and c/a and induces the distortion of the crystal structure. The increased b/a leads to a transverse asymmetry of the Na_0.5Bi_4.5-xCe_xTi₄O₁₅ ceramics, which facilitates the dipole flipping, thus enhancing the piezoelectric properties (d₃₃ = 20 pC/N). Although the improved c/a increases the degree of tetragonality of the Na_0.5Bi_4.5-xCe_xTi₄O₁₅ ceramic, which decreases the Curie temperature (T_C), the T_C values of all samples are higher than 600°C, considerably higher than the practical application temperature. The Ce doping significantly reduces the dielectric loss of the sample and increases its dielectric performance. The improvements in electric properties by the cerium doping can expand its use in high-temperature environments for oilfield logging, aerospace, and military applications.