Large enhancement of piezoelectric properties in Mn-modified SrBi4Ti4O15 and its thermal stabilities at elevated temperatures

Manganese-modified strontium bismuth titanate (SrBi₄Ti₄O₁₅, SBT) ceramic oxides were synthesized by substituting a small amount of manganese ions into the Ti⁴⁺ sites using conventional solid-state reaction. The resultant Mn-modified SBT (SBT-Mn) exhibits better piezoelectric properties in comparison to unmodified SBT. The piezoelectric properties of Mn-modified SBT is optimized with only 4 mol% Mn substitution. SBT-4Mn exhibits a large piezoelectric constant (d₃₃=30 pC/N), approximately twice the value of unmodified SBT (d₃₃=13 pC/N), while its Curie temperature, T_c, remains almost unchanged at ~530 °C. The temperature-dependent electrical impedance and electromechanical coupling factors k_p and k_t reveal that the SBT-4Mn exhibits thermally stable electromechanical coupling characteristics up to 300 °C but electromechanical coupling factors deteriorate significantly at a higher temperature due to increased conductivity. Our work suggested that Mn-modified SBT ceramics are promising materials for high temperature piezoelectric applications.     

The temperature-dependent piezoelectric and electromechanical properties of cobalt-modified sodium bismuth titanate

Lightly cobalt-modified, Aurivillius-type, sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) ceramics were synthesized by substituting a small amount of cobalt ions onto the Ti⁴⁺ sites using conventional solid-state reaction. X-ray photoelectron spectroscopy (XPS) analysis coupled with bond valence sum calculations show that the dopant cobalt ions substitute for Ti⁴⁺ ions in the form of Co³⁺. The resultant cobalt-modified NBT ceramics (NBT-Co) exhibit better piezoelectric and electromechanical properties by comparison with pure NBT. With only 0.3 wt% Co³⁺ substitution, the piezoelectric properties of the NBT-Co ceramics are optimal, exhibiting a high piezoelectric coefficient (d₃₃~33 pC/N), a low dielectric loss tan δ (~0.1% at 1 kHz), a high thickness planar coupling coefficient (k_t~34%) as well as a high Curie temperature (T_c~663 °C). Such NBT-Co ceramics exhibit nearly temperature-independent piezoelectric and electromechanical properties up to 400 °C, suggesting that these cobalt-modified NBT ceramics are promising materials for high temperature piezoelectric applications.     

Effects of (Li,Ce, Y) co-substitution on the properties of CaBi2Nb2O9 high temperature piezoceramics

High temperature lead-free Bismuth layer-structured (Li, Ce, Y)-substituted CBN piezoelectric ceramics were prepared by the solid-state reaction method. The phase structure, microstructure, piezoelectric property, dielectric property, thermal stability and electric property of the (Li, Ce, Y)-substituted CBN ceramics were studied. X-ray diffraction and SEM revealed the doped ceramics had typical bismuth layer-structure. The piezoelectric coefficient was improved significantly and the maximum value was ~16.1 pC/N.The Curie temperature of all the samples were in the range of 925–941 °C that was close to or even excess the value of pure CBN ceramics. The resistivity were studied deeply and all the samples possessed excellent resistivity at high temperature (500 °C, ~10⁶ Ω cm; 600 °C, ~10⁵ Ω·cm). The thermal depoling behavior of the ceramics was researched in detail and the doped ceramics exhibited outstanding thermal stability. All the results indicate the (Li, Ce, Y)-substituted CBN ceramics possesses preeminent property, making it promising for application especially in high temperature territories.     

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.     

Strong photoluminescence and good electrical properties in Eu-modified SrBi2Nb2O9 multifunctional ceramics

Bismuth layer-structured ferroelectric (BLSFs) ceramics of Sr_1−xEu_x Bi₂Nb₂O₉ (SBT-xEu, x=0.000, 0.002, 0.004, 0.006) were prepared by a conventional solid-state reaction method. All the samples have a bismuth oxide layered structure with a dense microstructure. The ferroelectric, piezoelectric, dielectric and optical properties of the ceramics were investigated. After Eu³⁺ doping, samples show a bright red photoluminescence upon blue light excitation of the 400–500 nm. Upon the excitation of 465 nm light, the materials have two intense emission bands peaking around 593 nm (yellow) and 616 nm (red). Meanwhile, good electrical properties with large piezoelectric constant d₃₃ of 14 pC/N and large remnant polarization 2P_r of 11.97 μC/cm² are obtained at x=0.006. Moreover, this material has a high Curie temperature (T_c=429 °C) and high resistivity, which makes the material resistant to thermal depolarization up to its Curie temperature. This feature indicates that the SBN-xEu ceramics have a latent use in high temperature applications.     

Lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3–CeO2 ceramics with high piezoelectric coefficient obtained by low-temperature sintering

Lead-free (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃–x%CeO₂(BCZT–xCe) piezoelectric ceramics have been prepared by the traditional ceramic process and the effects of CeO₂ addition on their phase structure and piezoelectric properties have been studied. The addition of CeO₂ significantly improves the sinterability of BCZT ceramics which results in a reduction of sintering temperature from 1540 °C to 1350 °C without sacrificing the high piezoelectric properties. X-ray diffraction data show that CeO₂ diffuses into the lattice of BCZT and a pure perovskite phase is formed. SEM images indicate that a small addition of CeO₂ greatly affects the microstructure. Main piezoelectric parameters are optimized at around x = 0.04 wt% with a high piezoelectric coefficient (d₃₃ = 600 pC/N), a planar electromechanical coefficient (k_p = 51%), a high dielectric constant (?_r = 4843) and a low dissipation factor (tan δ = 0.012) at 1 kHz, which indicates that the BCZT–xCe ceramics are promising for lead-free practical applications.     

Low temperature sintering and high piezoelectric properties of strontium doped PNZT–PNN ceramics processed via the columbite route

This study investigated the influence of strontium doping on both the sintering behavior and the piezoelectric properties of PNZT–PNN ceramics. The piezoelectric ceramics was produced by solid state reaction between metallic oxides, strontium carbonates (SrCO₃) and oxides precursors. NiNb₂O₆ precursors were mixed with the oxides to avoid the large-scale formation of pyrochlore phases during the sintering process and to favor the formation of the perovskite structure. Sintering experiments were accomplished between 900 °C and 1100 °C for PNZT–PNN with 0–4 mol% strontium. Dilatometer curves indicated that the densification of these samples occurs by 850 °C and the electromechanical characterization showed that strontium doping enhances the soft piezoelectric properties of the PZT–PNN ceramics.Consequently, a sintering temperature of 900 °C is sufficient to obtain doped PZT–PNN tablets with 99% of the theoretical density and excellent soft piezoelectric properties (ɛ_r > 4000; K_p > 60; d₃₃ > 1000 pm/V). This makes those ceramics suitable for the construction of high efficiency actuators with low sintering temperature. The low Curie temperature is the only drawback of this material for some applications such as engine fuel injection.     

Compositional inhomogeneity and segregation in (K0.5Na0.5)NbO3 ceramics

In this report, the effects of the calcination temperature of (K_0.5Na_0.5)NbO₃ (KNN) powder on the sintering and piezoelectric properties of KNN ceramics have been investigated. KNN powders are synthesized via the solid-state approach. Scanning electron microscopy and X-ray diffraction characterizations indicate that the incomplete reaction at 700 °C and 750 °C calcination results in the compositional inhomogeneity of the K-rich and Na-rich phases while the orthorhombic single phase is obtained after calcination at 900 °C. During the sintering, the presence of the liquid K-rich phase due to the lower melting point has a significant impact on the densification, the abnormal grain growth and the deteriorated piezoelectric properties. From the standpoint of piezoelectric properties, the optimal calcination temperature obtained for KNN ceramics calcined at this temperature is determined to be 800 °C, with piezoelectric constant d₃₃=128.3 pC/N, planar electromechanical coupling coefficient k_p=32.2%, mechanical quality factor Q_m=88, and dielectric loss tan δ=2.1%.     

Piezoelectric properties of Ca-modified Pb0.6Bi0.4(Ti0.75Zn0.15Fe0.10)O3 ceramics

Perovskite-structured Pb_0.6Bi_0.4(Ti_0.75Zn_0.15Fe_0.1)O₃ ceramics was reported with high Curie temperature T_C of 705 °C and tetragonality of c/a = 1.10, promising for high temperature applications with large piezoelectric anisotropy. In this paper, it was experimentally demonstrated to ease poling processing and enhance piezoelectricity through substituting lead with calcium of Pb_0.6?xCa_xBi_0.4(Ti_0.75Zn_0.15Fe_0.1)O₃. For the x = 0.18 sample, electromechanical coupling factor ratio of k_t/k_p → ∞, dielectric constant of 380, piezoelectric coefficient d₃₃ of 80 pC/N, mechanical quality factor Q_m of 50 and Curie point T_C of 237 °C were obtained, which exhibits better piezoelectric performance than the (Pb_0.76Ca_0.24)(Ti_0.96(Co_0.5W_0.5)_0.04)O₃. The enhanced piezoelectric response was analyzed with relation to the reduction of tetragonality and Curie temperature.     

Li2O excess (Na0.51K0.47Li0.02)(Nb0.8Ta0.2)O3 lead free piezoelectric ceramics

1 mol% Li₂O excess (Na_0.51K_0.47Li_0.02)(Nb_0.8Ta_0.2)O₃ ceramics were prepared by the conventional mixed oxide method and sintered from 950 to 1200 °C. Also, Li₂O was employed as a sintering aid for high densification and low temperature sintering process. X-ray diffraction results of 1 mol% Li₂O excess (Na_0.51K_0.47Li_0.02)(Nb_0.8Ta_0.2)O₃ lead free piezoelectric ceramics indicated that the specimens were well crystallized and have tetragonal structure. The specimens which sintered at 1050 °C showed the highest piezoelectric properties compared with others. The measured piezoelectric constant and electromechanical coupling coefficient were 231 pC/N and 38.9%, respectively. Curie temperature of (Na_0.51K_0.47Li_0.02)(Nb_0.8Ta_0.2)O₃ ceramics was 344.32, 344.4 and 344.5 °C at 1, 10 and 100 kHz, respectively.     

Synthesis and piezoelectric properties of Li-doped BaTiO3 by a solvothermal approach

Li-doped BaTiO₃ particles with the Li⁺ mole fraction, x, of 0–0.06 were synthesized by a solvothermal approach at 200 °C. The products consisted of nanoparticles of 50–100 nm in diameter. The sinterability and piezoelectric property of Li-doped BaTiO₃ were improved by doping with Li ion, i.e., the Li-doped BaTiO₃ samples could be sintered to almost full theoretical density (>95%) at a low temperature such as 1100 °C, and the highest piezoelectric constant, d₃₃ (260 pC/N) and electromechanical coupling factor, k_p (43.7%) could be realized at x value of 0.03. The Curie temperatures of all samples were around 130 °C, and did not change very much depending on the amount of Li-doping.     

Low-temperature sintering and electrical properties of (K,Na)NbO3 based lead-free ceramics with high Curie temperature

Lead-free ceramics (1 ? x)(K_0.48Na_0.52)NbO₃–(x/5.15)K_2.9Li_1.95Nb_5.15O_15.3 (x = 0.3–0.6, KNN–KLN100x) were prepared by conventional sintering technique at a low temperature of 960 °C. The effects of KLN contents on microstructure, dielectric, and piezoelectric properties were investigated. After the addition of KLN, the sintering performance and Curie temperature of the ceramics were markedly improved. The ceramics with x = 0.3 exhibited very good piezoelectric properties: d₃₃ = 138 pC/N, k_p = 45.03%, T_c = 495 °C, the dielectric constant at room temperature ?_r (RT) = 478 and the maximum dielectric constant ?_r (max) = 5067. These results indicated that the KNN–KLN100x lead-free ceramics sintered at low temperatures are promising for high temperature piezoelectric applications.     

Densification behavior and electrical properties of CuO-doped Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 ternary ceramics

CuO modified Pb(In_1/2Nb_1/2)O₃–Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PIN–PMN–PT) ternary relaxor based ferroelectrics with the composition near the morphotropic phase boundary were synthesized by two-step columbite precursor method. The introduction of CuO significantly improved the sinterability of PIN–PMN–PT ceramics, resulting in the full densification of samples at lower sintering temperatures. It also profoundly modified the crystal structure and fracture mode of the ceramics. Properly increasing CuO content led to the disappearance of rhombohedral-tetragonal phase transition, remarkably improved the Curie temperature (T_c), and made the ceramics more relaxorlike. The ternary ceramics doped with 0.25 wt% CuO possessed optimum piezoelectric properties (d₃₃=584 pC/N, d₃₃^*=948 pC/N, and k_p=0.68), high ferroelectric properties (E_c=9.9 kV/cm, and P_r=33.1 μC/cm²), low dielectric loss (tan δ=0.9%), and wider temperature usage range (T_c=225 °C). The obtained properties are much higher than those of previously reported PIN–PMN–PT based ceramics, indicating that CuO doped PIN–PMN–PT is a promising candidate for electromechanical applications with high performance and wide temperature/electric field usage ranges.     

Influence of calcination temperature on the piezoelectric properties of Ag2O doped 0.94(K0.5Na0.5)NbO3–0.06LiNbO3 ceramics

The effects of calcination temperature on the bulk density, piezoelectric, and ferroelectric properties were investigated for the Ag₂O doped 0.94(K_0.5Na_0.5)NbO₃–0.06LiNbO₃ ceramics. The calcination temperatures were varied from 750 to 950 °C by 50 °C differences. An tetragonal XRD pattern, consistent with single-phase 0.94(K_0.5Na_0.5)NbO₃–0.06LiNbO₃ was obtained after calcination at 850 °C for 2 h. And the experimental results showed that Ag₂O doped 0.94(K_0.5Na_0.5)NbO₃–0.06LiNbO₃ ceramics calcined at 850 °C had a remnant polarization P_r=24.5 μC/cm², bulk density=4.32 g/cm³, piezoelectric constant d₃₃=282 pC/N and electromechanical coefficient k_p=37.8%.     

Effects of Ta-substitution on the dielectric properties of Ba6Ti2(Nb1−xTax)8O30 thin films

Tunable Ba₆Ti₂(Nb_1−xTa_x)₈O₃₀ (BTN-xTa; x = 0, 0.25, 0.4) thin films with a tetragonal tungsten bronze structure (TTB) were deposited on platinized Si substrates using the pulsed laser deposition (PLD) technique and their properties were investigated from the viewpoint of orientation and ferroelectric phase transition. Crystal structures and dielectric properties were characterized using an X-ray diffractometer and an impedance analyzer. Pure BTN (BTN-0Ta) thin films showed tunability as high as 60% and the tunability decreased as the amounts of Ta-substitution increased at 150 kV/cm and at 1 MHz. The dielectric constants also decreased from 436 to 88 at 1 MHz through the Ta-substitution. The low tunability and dielectric constants of Ta-substituted thin films were mainly ascribed to the lowered ferroelectric transition temperature (T_c). Ferroelectric BTN (BTN-0Ta) thin films may have been changed into a paraelectric state through the Ta-substitution since the T_c of BTN thin films were shifted to temperatures far below room temperatures (approximately −60 °C).     

Reduced dielectric loss and strain hysteresis in (0.97−x)BiScO3–xPbTiO3–0.03Pb(Mn1/3Nb2/3)O3 piezoelectric ceramics

(0.97−x)BiScO₃–xPbTiO₃–0.03Pb(Mn_1/3Nb_2/3)O₃ (BS–PT–PMnN) ceramics were prepared by solid-state reaction method. X-ray diffraction analysis revealed that the morphotropic phase boundary (MPB) of BS–PT–PMnN ceramics located near x=0.58. The high Curie temperature (437 °C), large piezoelectric constant (300 pC/N), low dielectric loss (0.015) and small strain hysteresis (20%) were obtained for the MPB composition. Its dielectric loss and strain hysteresis were reduced down to one third and half those of pure BiScO₃–PbTiO₃ (BS–PT) ceramics, respectively. In addition, the maximum vibration velocity of the BS–PT–PMnN ceramics was 0.85 ms⁻¹, much superior to those of BS–PT (0.15 ms⁻¹) and modified PZT (0.4 ms⁻¹) ceramics. These results indicated BS–PT–PMnN ceramics were promising candidates for high temperature piezoelectric applications.     

Processing and enhanced electrical properties of Sr1-x(K0.5Bi0.5)xBi2Nb2O9 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics, Sr_1−x(K_0.5Bi_0.5)_xBi₂Nb₂O₉ (SKBN-x, x=0, 0.2, 0.5, 1.0), were synthesized by a conventional solid-state reaction. Structural and electrical properties of SKBN-x ceramics were investigated. X-ray diffraction analysis suggested that the substitution led to the formation of a layered perovskite structure. Plate-like morphologies for the grains were clearly observed in all the samples, which are characteristic for layer-structure Aurivillius compounds. The Curie temperature (T_c) is found to shift to higher temperature from 445 °C to 509 °C with increasing (K, Bi) content. Excellent remanent polarization (2P_r∼15 μC/cm²) were obtained for SKBN-0.2 ceramic. High piezoelectric coefficient of d₃₃∼21  pC/N were obtained for the samples at x=0.5. Additionally, thermal annealing studies indicated that the piezoelectric coefficient (d₃₃) of SKBN-0.5 was unchanged even if annealing temperature increased to be 450 °C, demonstrating the ceramics are the promising candidates for high-temperature applications.     

Structural,dielectric, and piezoelectric properties of fine-grained NBT–BT0.11 ceramic derived from gel precursor

(Na_1/2Bi_1/2)TiO₃ doped in situ with 11 mol% BaTiO₃ (NBT–BT_0.11) powders were synthesized by a sol–gel method, and the electrical properties of the resulting ceramics were investigated. The powders consisting of uniform and fine preliminary particles of about 50 nm were prepared by calcining the gel precursor at 700 °C. (Na_1/2Bi_1/2)_0.89Ba_0.11TiO₃ ceramics, sintered at temperatures up to 1150 °C have a rhombohedral symmetry, while the ceramic sintered at 1200 °C exhibits a tetragonal crystalline structure. The ceramics show high dielectric constant (?_r ～ 5456), dielectric loss of 0.02, depolarization temperature T_d ～ 110 °C and temperature corresponding to the maximum value of dielectric constant T_m ～ 262 °C. The dielectric constant (?₃₃) and the piezoelectric constant (d₃₃) attain the maximum values of 924 and 13 pC/N, respectively, while the electromechanical coupling factor (k_p) value is 0.035. The NBT–BT_0.11 ceramics derived from sol–gel present high mechanical quality factor (Q_m ～ 860). The dielectric and piezoelectric properties values of NBT–BT_0.11 ceramics derived from sol–gel are smaller than those of samples produced by the conventional solid state reaction method, due to the grains size and oxygen vacancies that generate dipolar defects.     

Synthesis of (K,Na) (Nb,Ta)O3 lead-free piezoelectric ceramic powders by high temperature mixing method under hydrothermal conditions

A facile hydrothermal route via high temperature mixing method was used to synthesize (K, Na) (Nb, Ta)O₃ lead-free piezoelectric ceramic powders. The influence of Ta doping and K⁺/(K⁺ + Na⁺) molar ratios in the starting solution on the resultant powders were investigated by X-ray diffraction, scanning electron microscope, transmission electron microscopy, and selected area electron diffraction. The Ta element was successfully doped into the alkaline niobate structure to form crystalline (K, Na) (Nb, Ta)O₃ lead-free piezoelectric ceramics powder. The microstructure, piezoelectric, ferroelectric, and dielectric properties of the sintered (K, Na) (Nb, Ta)O₃ ceramics from the obtained powders were investigated. The piezoelectric coefficient (d₃₃), electromechanical coupling coefficient (k_p), dielectric constant (?_r), and remnant polarization (P_r) of the sample sintered at 1180 °C show optimal values of 210 pC/N, 34.0%, 2302, and 19.01 μC/cm², respectively.