High performance Aurivillius-type bismuth titanate niobate (Bi3TiNbO9) piezoelectric ceramics for high temperature applications

This paper reports the significant improved piezoelectric properties of high temperature bismuth titanate niobate (Bi₃TiNbO₉, BTN) polycrystalline ceramics. The piezoelectric performance of BTN ceramics is significantly enhanced by cerium modifications. The dielectric measurements indicate that the Curie temperature T_c gradually decreases over the temperature range of 907–889 °C with cerium contents increasing up to 0.7 wt%. The BTN-5Ce (BTN+0.5 wt% CeO₂) exhibits optimized piezoelectric properties with a piezoelectric constant d₃₃ of 16 pC/N, which is five times the value of unmodified BTN (d₃₃~3 pC/N), while BTN-5Ce maintains a high Curie temperature T_c of 894 °C. The temperature-dependent electrical impedance and electromechanical coupling factors (k_p, and k_t) reveal that the BTN-5Ce exhibits thermally stable electromechanical coupling characteristics up to 500 °C but significantly deteriorates at 600 °C due to high conductivity at a higher temperature. The thermally stable electromechanical properties in combination with the ceramics׳ high electrical resistivity (10⁶ Ω cm at 500 °C) and high Curie temperature (~900 °C) demonstrate that cerium-modified BTN ceramics are good materials for high temperature sensing 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.     

Creating adjoining polymorphic phase transition (PPT) regions in ferroelectric (Ba,Sr)(Zr,Ti)O3 ceramics

In this work, we report the polymorphic phase transitions(PPT) in ferroelectric Ba_0.95Sr_0.05Zr_xTi_(1-x)O₃ (BSZT, x = 0.01–0.10) ceramics synthesized by using a solid-state reaction method. The doping elements and composition ratios were selected to create adjoining PPT phase boundaries near room temperature, hence to achieve a broadened peak of piezoelectric performance with respect to composition. The temperature-composition phase diagram was constructed and the effects of PPT on the electromechanical and ferroelectric properties of the ceramics were investigated. It was revealed that the two adjacent PPT regions at room temperature showed different characteristics in property enhancement. However, due to the proximity of the phase boundaries, Ba_0.95Sr_0.05Zr_xTi_(1-x)O₃ ceramics in a fairly broad range of compositions (0.02 ≤ x ≤ 0.07) showed excellent piezoelectric properties, including a large piezoelectric constant (312 pC/N ≤ d₃₃ ≤ 365 pC/N) and a high electromechanical coupling coefficient k_p (0.42 ≤ k_p ≤ 0.49).     

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.     

Property improvement of 0.3Pb(Zn1/3Nb2/3)O3-0.7Pb0.96La0.04(ZrxTi1−x)0.99O3 ceramics by hot-pressing

The piezoelectric ceramics of the compositions expressed by the formula: 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb_0.96La_0.04(Zr_xTi_1−x)_0.99O₃ (x = 0.50–0.53) were prepared by two kind of sintering processes: conventional sintering (CS) and hot-pressing (HP) sintering. By comparing the properties of these two series of ceramics, piezoelectric coefficients (d₃₃), electromechanical coupling factors (k_p), dielectric constants (ɛ_r), etc. were enormously improved by HP sinter procedure, which can be attributed to the highly dense microstructure (bulk density >99%). The most impressive results are the d₃₃ (845pC/N) and k_p (0.703) in the HP specimen with Zr/Ti = 51/49, which have not been observed in the previous relative reports. Additionally, according to the contrast of the experiment data, the origin of the property improvement was analyzed in details.     

Morphotropic phase boundary in the BNT–BT–BKT system

Lead-free x Bi_0.5Na_0.5TiO₃–y BaTiO₃–z Bi_0.5K_0.5TiO₃ piezoelectric ceramics were synthesized by a conventional solid state reaction method. The microstructure, ferroelectric and piezoelectric properties of the ceramics were investigated. Structure measurements by X-ray diffraction with Rietveld refinement have allowed us to specify more precisely the morphotropic phase boundary (MPB) in this system. For (1 ? x) BNT–x BT solid solution ceramics, the 0.94 BNT–0.06 BT morphotropic composition shows the higher values with d₃₃ = 170 pC/N, k_p = 0.35 and k_t = 0.53. In the case of (1 ? x) BNT–x BKT compositions, the d₃₃, k_p and k_t are, respectively, 137 pC/N, 0.39 and 0.54 for the 0.80 BNT–0.20 BKT ceramic. On the other hand, the ternary 0.865 BNT–0.035 BT–0.100 BKT morphotropic composition shows high piezoelectric constant and electromechanical coupling factors (d₃₃ = 133 pC/N, k_p = 0.26 and k_t = 0.57).     

Textured (K0.5Na0.5)NbO3 ceramics prepared by screen-printing multilayer grain growth technique

The screen-printing multilayer grain growth (MLGG) technique is successfully applied to alkaline niobate lead-free piezoelectric ceramics. Highly textured (K_0.5Na_0.5)NbO₃ (KNN) ceramics with 〈0 0 1〉 orientation (f = 93%) were fabricated by MLGG technique with plate-like NaNbO₃ templates. The influence of sintering temperature on grain orientation and microstructure was studied. The textured KNN ceramics showed very high piezoelectric constant d₃₃ = 133 pC/N, and high electromechanical coupling factor k_p = 0.54. These properties were superior to those of conventional randomly oriented ceramics, and reach the level of those of textured KNN ceramic prepared by tape-casting technique. Compared with other grain orientation techniques, screen-printing is a simple, inexpensive and effective method to fabricate grain oriented lead-free piezoelectric ceramics.     

Grain size effect on piezoelectric and ferroelectric properties of BaTiO3 ceramics

A series of dense barium titanate (BaTiO₃, BTO) ceramics with different grain sizes (GS) were prepared by two-step sintering method. The effect of GS on piezoelectric coefficient (d₃₃) and planar electromechanical coupling factor (k_p) displayed a trend similar to that on relative permittivity (ɛ′). The values of d₃₃, k_p, and ɛ′ increased significantly with decreasing GS, reaching maximum values (ɛ′ = 6079, d₃₃ = 519 pC/N and k_p = 39.5%) at approximately 1 μm, and then decreased rapidly with further decreasing GS. The results revealed that high-performance BTO ceramics could be effectively prepared by controlling GS. Polarization–electric field hysteresis loops and temperature dependence of ɛ′ were also investigated.     

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.     

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%.     

Effect of CuO addition on magnetic and electrical properties of Sr2Bi4Ti5O18 lead-free ferroelectric ceramics

The effect of CuO addition on magnetic and electrical properties of Sr₂Bi₄Ti₅O₁₈ (SBT) lead-free bismuth layered structure ferroelectric ceramics have been studied and reported. Interestingly, the prepared samples exhibit multiferroic behavior with the coexistence of magnetic and ferroelectric phase transition temperature. Magnetic phase transition with Neel׳s temperature (T_N) of 657 K is observed at 0.75 mol% of CuO added SBT ceramics, which is higher than the well known multiferroic BiFeO₃ (643 K) and the ferroelectric phase transition with Curie temperature (T_C) of 587 K is observed at 1 mol% of CuO added SBT ceramics, which is relatively higher than the reported pure SBT ceramics (558 K). Further, the electrical properties such as dielectric, ferroelectric, piezoelectric, leakage current density characteristics and optical properties were investigated as a function of x (x=0, 0.25, 0.5, 0.75 and 1 mol%). Presence of strong magnetic super-exchange interactions in CuO and the creation of oxygen vacancies play a vital role in the enhancement of magnetic and electrical properties of CuO doped SBT ceramics. Moreover, the present results indicate that, small amount (0.25 mol%) of CuO addition in SBT ceramics enhances the electrical properties significantly and vice versa, large amount (0.75 mol%) of CuO addition enhances the magnetic properties. Thus, the presence of magneto-electric coupling effect was observed in CuO doped Sr₂Bi₄Ti₅O₁₈ ferroelectric ceramics.     

Effect of Fe substitution on the piezoelectric,dielectric and ferroelectric properties of PNZST ceramics

Fe-doped (Pb_0.99Nb_0.02)[(Zr_0.70Sn_0.30)_0.52Ti_0.48]_0.98O₃ (PNZST) ceramics were prepared via conventional solid state reaction method, and the effect of Fe doping on their structural and electrical properties was investigated in detail. Results showed that Fe³⁺ cations could dissolve into readily the B-sites of perovskite structure for the PNZST ceramics with the less amount of Fe content (≤0.8 wt%), resulting in the full densification after sintered at 1300 °C. Meanwhile, Fe doping caused a structure transform from the tetragonal to the rhombohedral. The better electric properties for PNZST ceramic with 0.6 wt% Fe content were obtained, i.e. piezoelectric constant d₃₃=380 pC/N, electromechanical coupling factor k_p=0.57, mechanical quality factor Q_m=225, dielectric constant ε_r=1190, loss tangent tan δ=0.007 and curie temperature T_c=318 °C.     

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.     

Effects of ZnO/Li2O codoping on microstructure and piezoelectric properties of low-temperature sintered PMN–PNN–PZT ceramics

Pb(Mg_1/3Nb_2/3)O₃–Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr_1/2Ti_1/2)O₃ (designated as PMNT) piezoelectric ceramics codoping with Zn²⁺/Li⁺ were prepared and the effects of ZnO/Li₂O (Z/L) additive on microstructure, piezoelectric and dielectric properties were investigated. The results show that the pure perovskite phase is formed and the phase structure changes from tetragonal to rhombohedral with different Z/L weight ratios. The Curie temperature T_c, dielectric constant ?, electromechanical coupling factor k_p and piezoelectric constant d₃₃ decrease, whereas mechanical quality factor Q_m increases with Z/L weight ratio changing from 1:1 to 1:8. The optimized Z/L weight ratio is 1:1. It is revealed that k_p and d₃₃ first increase then decrease, whereas Q_m changes opposite with increasing content of Z/L additive. The PMNT ceramic with Z/L ratio 1:1 and the amount of 1 wt% has excellent piezoelectric properties: k_p = 0.60, d₃₃ = 397 pC/N, T_c = 251 °C, Q_m = 150, ? = 2628 and tan δ = 0.0296, when sintered at 960 °C. Finally, multilayer piezoelectric actuator is prepared using optimal composition by tape casting. The actuator shows the displacement characteristics of 3.3 μm under electric field 100 V/mm.     

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.     

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.     

X-ray diffraction,dielectric, pyroelectric,piezoelectric and Raman spectroscopy studies on (Ba0.95Ca0.05)0.8875Bi0.075TiO3 ceramic

The (Ba_0.95Ca_0.05)_0.8875Bi_0.075TiO₃ ceramic composition was prepared using the conventional mixed-oxide technique. X-ray diffraction at room temperature and dielectric permittivity in the temperature range from 85 to 450 K and frequency range from 10² to 2 × 10⁵ Hz, respectively, were studied. The X-ray spectra were investigated by profile refinement technique with the use of specialized software at room temperature, the (Ba_0.95Ca_0.05)_0.8875Bi_0.075TiO₃ composition crystallizes in quadratic perovskite structure. The dielectric measurements show classical ferroelectric behavior. The pyroelectric and piezoelectric results confirm the dielectric measurements. The pyroelectric coefficient is about 69.2 nC/cm² K at the transition temperature (T_C = 367 K). The piezoelectric constant is d₃₁ = 31.1 pC/N and the electromechanical coupling factor is k_P = 0.14679. Raman spectra of (Ba_0.95Ca_0.05)_0.8875Bi_0.075TiO₃ ceramic were taken at various temperatures and measured over the wave number range from 50 to 1000 cm^?1. All the Raman bands were assigned as the transitional modes of Ba²⁺, Ca²⁺, Bi³⁺ and Ti⁴⁺ cations. The temperature evolution of Raman spectra across the transition shows an important evolution characterizing the disorder of the high temperature phase.     

High piezoelectricity in CuO-modified Ba(Ti0.90Sn0.10)O3 lead-free ceramics with modulated phase structure

High piezoelectricity was achieved in Ba(Ti_0.90Sn_0.10)O₃ lead-free ceramics by optimizing CuO addition and sintering temperature. The phase structure of 1.0 mol% CuO-doped Ba(Ti_0.90Sn_0.10)O₃ ceramic is coexisting rhombohedral and tetragonal phases as sintered at 1300 °C. The coexistence of rhombohedral, tetragonal and orthorhombic phases appears in 1.0 mol% CuO-doped Ba(Ti_0.90Sn_0.10)O₃ ceramics as sintered at 1350–1450 °C, which leads to highly enhanced d₃₃ up to 650pC/N. This work demonstrates that high piezoelectric property (d₃₃ = 650pC/N) can be obtained in BaTiO₃-based lead-free piezoceramics with a simple composition modification by modulating phase structures, which also indicates that Ba(Ti,Sn)O₃ is a promising candidate to replace the lead-based piezoceramics.     

Grain size effect on electrical properties of Mn-modified 0.67BiFeO3–0.33BaTiO3 lead-free piezoelectric ceramics

To investigate how grain size affects the dielectric, ferroelectric, and piezoelectric properties of Mn-modified 0.67BiFeO₃–0.33BaTiO₃ ceramics, we prepared samples with a wide variety of grain sizes from 4.1 μm to 0.59 μm via a conventional solid-state process that use the normal and the two-step sintering methods. Small-signal dielectric measurements show that all the samples exhibit a relaxor-like behavior and that grain size has little influence on the room-temperature dielectric permittivity. For grain sizes below 2 μm, the remanent polarization P_r and piezoelectric coefficient d₃₃ decrease with the grain size, whereas they remain almost constant near P_r = 27 μC/cm² and d₃₃ = 70 pC/N in samples with grain sizes exceeding 2 μm. The mechanism underlying the observed grain size effect is discussed in terms of the electric-field-induced formation of macroscopic ferroelectric domains.