Dielectric and piezoelectric properties of Li-substituted lead-free (Bi0.5Na0.5)TiO3–(Bi0.5K0.5)TiO3–BaTiO3 ceramics

Lead-free 0.79(Bi_0.5Na_0.5)TiO₃–0.14[Bi_0.5(K_0.5−xLi_x)]TiO₃–0.07BaTiO₃ (BNBK79 + xLi, x = 0.0, 0.1, 0.2, 0.25, 0.3, and 0.4) ceramics were prepared by conventional solid state reaction process. The crystalline structures and surface morphologies are investigated by X-ray diffraction method and scanning electron microscopy. Dielectric and piezoelectric properties were measured. With increasing of lithium substitution, the Curie temperatures of BNBK79 + xLi ceramics increase, but the maximum value of the dielectric constant decreases. And a relatively large remnant polarization of 17.6 μC/cm² and 157 pC/N of d₃₃ has been obtained when x = 0.3.     

Phase-transformation-induced microstructure in lead-free ferroelectric ceramics based on (Bi0.5Na0.5)TiO3–BaTiO3–(Bi0.5K0.5)TiO3

Lead-free ferroelectric ceramics with a morphotropic phase boundary (MPB) composition 85.4% (Bi_0.5Na_0.5)TiO₃–2.6%BaTiO₃–12.0% (Bi_0.5K_0.5)TiO₃ (BNT-BT-BKT at a molar ratio of 85.4: 2.6: 12.0) doped with 0.8?mol% Nb₂O₅ were studied for their crystalline phases and microstructure. The crystalline phases were identified using X-ray diffractometry (XRD) with the contents determined using the Rietveld refinement technique. The phase-transformation-induced microstructure was analyzed using transmission electron microscopy (TEM) and the crystal symmetries were determined using the convergent-beam electron diffraction (CBED) technique. Samples sintered at 1200°C contain a mixture of cubic (C-), tetragonal (T-) and rhombohedral (R-) phases at a ratio of C/T/R?=?56.6: 28.4: 15.0?wt%. Two types of grains are produced: one characterized by a featureless contrast consisting of nano-scale T-domains dispersed in a C-phase matrix; the other a core-shell structure with a shell containing twin and anti-phase-boundary (APB) domains coexisting with a (C?+?T)-phase mixture core. The T- and R-twin boundaries are determined to {111}_T and {110}_R, respectively, and the fault vector for T-APB to R?=?1/2?110]_T. The characteristic microstructure is discussed in terms of the reduction in the point group symmetry and changes in the unit cell volume or the Bravais lattice upon phase transformation among the C-, T- and R-phases. The twin and the APB domains are induced and explained.     

Microstructure and electrical properties of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–LiNbO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics of (1?x?y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yLiNbO₃ (BNT–BKT–LN-x/y) have been fabricated by a conventional solid-state reaction method, and their microstructure and electrical properties have been investigated. The results of X-ray diffraction (XRD) measurement show that K⁺, Li⁺ and Nb⁵⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a solid solution with a pure perovskite structure. The BKT and LN addition has no remarkable effect on the crystal structure. However, a significant change in grain size took place. Simultaneously, with increasing amount of LN, the temperature for a ferroelectric–antiferroelectric phase transition is clearly reduced. The temperature dependence of dielectric properties suggests that the ceramics have diffuse-type phase transition characteristics. The piezoelectric constant d₃₃ and the electromechanical coupling factor k_p of the ceramics attain maximum values of 195 pC/N and 0.336 at x=0.18 and y=0.01.     

Effect of Li-substitution on piezoelectric and ferroelectric properties of (Bi0.92Na0.92−xLix)0.5Ba0.06Sr0.02TiO3 lead-free ceramics

New lead-free ceramics (Bi_0.92Na_0.92−xLi_x)_0.5Ba_0.06Sr_0.02TiO₃ have been fabricated by a conventional ceramic technique and their electrical properties have been studied. X-ray diffraction studies reveal that Li⁺, Ba²⁺ and Sr²⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a new solid solution with a pure perovskite structure. The partial substitution of Li⁺ for Na⁺ increases the remanent polarization P_r of the ceramics. Because of the large P_r and low coercive field E_c, the ceramics with x = 0.075–0.125 exhibit excellent piezoelectric properties: d₃₃ = 189–235 pC/N, k_p = 33.6–36.3% and k_t = 51.6–54.3%. The ceramics exhibit relaxor behaviors after the substitution of Li⁺ for Na⁺. Our results also suggest that polar and non-polar phases may coexist in the ceramics at temperatures above the depolarization temperature T_d.     

Phase transition,dielectric and piezoelectric properties of NaNbO3–Bi0.5Li0.5TiO3 lead-free ceramics

Lead-free ceramics (1?x)NaNbO₃–xBi_0.5Li_0.5TiO₃ have been fabricated by an ordinary sintering technique, and their electric properties and temperature characteristics have been studied. All the ceramics possess a perovskite structure with orthorhombic symmetry, indicating that (Bi_0.5Li_0.5)TiO₃ diffuses into NaNbO₃ lattices to form a new solid solution. A low (Bi_0.5Li_0.5)TiO₃ doping level transforms the NaNbO₃ ceramics from antiferroelectric to ferroelectric. The ceramics with x ≤ 0.075 are normal ferroelectric, and the ferroelectric-paraelectric phase become diffusives with the doping level of Bi_0.5Li_0.5TiO₃ increasing. As x increases, the Curie temperature of the ceramics decreases linearly, while the relative permittivity ε_r increases. 0.925NaNbO₃–0.075(Bi_0.5Li_0.5)TiO₃ ceramic exhibits the relatively large piezoelectric constant (d₃₃ = 58 pC/N), high Curie temperature (T_C = 228 °C) and good temperature stability, suggesting that the ceramics are one of new possible candidates for lead-free piezoelectric materials.     

Dielectric,electromechanical coupling properties of Mn-doped Na0.5Bi0.5TiO3–BaTiO3 lead-free single crystal

Applied Physics A - Mn-doped 0.948Na0.5Bi0.5TiO3–0.052BaTiO3 (NBBT94.8/5.2) lead-free single crystal with excellent piezoelectric and electromechanical coupling properties was successfully...     

Ferroelectric relaxor properties of (1 − x)K0.5Na0.5NbO3–xBa0.5Ca0.5TiO3 ceramics

The Ba_0.5Ca_0.5TiO₃ (BCT) composition dependent dielectric and structural properties of (1?x)K_0.5Na_0.5NbO₃–xBa_0.5Ca_0.5TiO₃ powders were investigated. Room temperature x-ray diffraction revealed the powder structure to transform from orthorhombic to cubic with increasing BCT composition. The frequency dependent dielectric constant measurements revealed a shift in the temperature of the maximum dielectric constant for at frequencies, suggesting that the system exhibits ferroelectric relaxor behavior. The system containing 15% BCT showed the closest calculated Curie–Weiss exponent to 2, which the exponent for a relaxor ferroelectric.     

Dielectric,thermal and Raman spectroscopy studies of lead-free (Na0.5Bi0.5)1−xSrxTiO3 (x = 0, 0.04 and 0.06) ceramics

ABSTRACT

Lead-free (Na_0.5Bi_0.5)_1?xSr_xTiO₃ (x = 0, 0.04 and 0.06) ceramics with relative densities above 97% were prepared by solid-state synthesis process. Their dielectric, thermal and Raman properties were studied. X-ray diffraction analysis shows perovskite structure with rhombohedral symmetry at room temperature. Sr doping of Na_0.5Bi_0.5TiO₃ (NBT) results in an increase of the dielectric permittivity, diffusing of the permittivity maximum and its shift toward lower temperatures. The temperature of the rhombohedral–tetragonal phase transition indicated by the differential scanning calorimetry (DSC) peak and relaxational dielectric anomaly near the depolarization temperature are also shifted toward lower temperatures. The observed increase and broadening of the permittivity maximum, enhancement of the dielectric relaxation near the depolarization temperature, broadening of the DSC anomaly related to the rhombohedral–tetragonal phase transition and broadening of the Raman bands with increasing Sr content are attributed to the increase of the degree of cationic disorder and evident enhancement of the relaxor-like features in NBT–xST. This enhancement could play a positive role in the improvement of the piezoelectric performance of NBT-based ceramics.     

Phase structure,electrical properties,and stability of 0.96(K0.48Na0.52)1−xLixNbO3–0.04Bi0.5Na0.5ZrO3 lead-free piezoceramics

In this work, 0.96(K_0.48Na_0.52)_1−xLi_xNbO₃–0.04Bi_0.5Na_0.5ZrO₃ lead-free piezoceramics were prepared using the conventional solid state reaction method in order to attain both a high T_C and an enhanced d₃₃. The effect of Li content on their phase structure, electrical properties, and stability was systematically investigated. These results indicate that adding Li could result in the increase of T_C and the decrease of T_O–T. Here we obtain the ceramics with an orthogonal–tetragonal phase boundary in the composition of x = 0.02, and then enhanced piezoelectric properties and a high Curie temperature (i.e., d₃₃ ∼ 255 pC/N, k_p ∼ 41%, and T_C ∼ 360 °C) were observed, showing the realization of our objective. In addition, a good stability of piezoelectric and ferroelectric properties has been shown in such a material system.     

(1-x)(K0.5Na0.5)NbO3-xSrTiO3陶瓷的弛豫铁电性能

通过对(1-x)(K0.5Na0.5)NbO3-xSrTiO3(0≤x≤0.15)陶瓷的相组成、晶体结构和介电性能的研究发现,该陶瓷为单一的钙钛矿结构相.当x含量较小(x＜0.1)时为正交相结构,x≥0.1时转变为四方相结构.随着SrTiO3掺杂量的增加,样品的致密度增加,样品由正常铁电相逐渐向弥散铁电相转变,且相变温度明显下降,其相变峰的半高宽D和临界指数γ,随 x 的增加而增加.样品损耗ε″r(复介电常数虚部)随温度T的变化表明低温时弛豫极化损耗起主要作用,高温时漏导损耗起主要作用.同时介电常数实部ε′r随频率的变化显示(1-x)(K0.5Na0.5)NbO3-xSrTiO3弛豫为德拜弛豫.     

Dielectric and piezoelectric properties of (Bi1−x−yNdxNa1−y)0.5BayTiO3 lead-free ceramics

New lead-free (Bi_1−x−yNd_xNa_1−y)_0.5Ba_yTiO₃ ceramics were prepared by a conventional ceramic technique and their dielectric and piezoelectric properties were studied. X-ray diffraction studies reveal that Nd³⁺ and Ba²⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a new solid solution with a pure perovskite structure, and a morphotropic phase boundary (MPB) of rhombohedral and tetragonal phases is formed at 0.04 < y < 0.10. The partial substitutions of Nd³⁺ and Ba²⁺ decrease effectively the coercive field E_c and increase significantly the remanent polarization P_r. Because of lower E_c, larger P_r and the formation of the MPB, the piezoelectric properties of the ceramics are significantly enhanced at x/y = 0.02/0.06: d₃₃ = 150 pC/N and k_p = 30.5%. The ceramics exhibit relaxor characteristic, which is probably resulted from the cation disordering in the 12-fold coordination sites. The depolarization temperature T_d shows a strong compositional dependence and reaches a minimum value at the MPB. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics may contain both the polar and non-polar regions near the depolarization temperature T_d, which cause the polarization hysteresis loop become deformed near/above T_d.     

Thermal,Raman and dielectric study of 0.5K0.5Bi0.5TiO3–0.5PbTiO3 ceramics

The 0.5K_0.5Bi_0.5TiO₃–0.5PbTiO₃ ceramics were prepared by following a standard solid-state method. The Raman, thermal and dielectric properties of these ceramics were investigated. The X-ray measurements showed that samples have single perovskite-type structure with tetragonal symmetry. Dielectric study revealed that the dielectric behaviour of the investigated ceramics is rather of normal ferroelectrics with large thermal hysteresis. The transition temperature observed by means of differential scanning calorimetry measurements is in good agreement with that obtained from dielectric study.     

Raman spectra and anomalies of dielectric properties and thermal expansion of lead-free (1−x)Na0.5Bi0.5TiO3-xSrTiO3 (x = 0, 0.08 and 0.1) ceramics

ABSTRACT

Thermal expansion, Raman and dielectric properties of the lead-free (1?x)Na_0.5Bi_0.5TiO₃-xSrTiO₃ (x = 0, 0.08 and 0.1) ceramic solid solutions, fabricated by the conventional solid-state reaction method, were investigated. The Sr-doping results in an increase of the dielectric permittivity, broadening of the permittivity maximum, enhancement of the relaxation near depolarization temperature, broadening of the Raman bands and shift of all anomalies toward lower temperatures. The observed effects are attributed to an increase of the degree of cationic disorder and enhancement of the relaxor-like features. Anomalies in the thermal expansion strain were observed at the temperatures corresponding to the dielectric anomalies but not related to any phase transitions. These anomalies are supposed to follow changes of the averaged unit cell volume in the temperature interval of tetragonal and rhombohedral phase coexistence.     

Structure and electrical properties of trilayered BaTiO3/(Na0.5Bi0.5)TiO3–BaTiO3/BaTiO3 thin films deposited on Si substrate

Highly (110)-oriented trilayered BaTiO₃ (25 nm) /(Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ (300 nm) / BaTiO₃ (25 nm) thin films were deposited on Pt/Ti/SiO₂/Si substrates via chemical solution deposition. It was found that the inserted bottom BaTiO₃ layer between Pt and (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ is very effective for promoting the crystallinity and (110)-oriented growth of NBT-BT films. Meanwhile, the BaTiO₃ layers also provide better interfaces between the ferroelectric thin film and the electrodes in terms of reducing leakage current. The trilayered films showed enhanced dielectric and ferroelectric properties compared with the pure NBT-BT films. Well saturated hysteresis loops were obtained due to good electrical insulating properties in the high electric field region.     

Dielectric,structural and specific heat properties of lead-free [(1−x)(Na0.5Bi0.5)−xBa]Zr1−yTiyO3 ceramics (x = 0.06, 0.085, 0.09, 0.1 and y = 0.97)

Lead-free [(1?x)(Na_0.5Bi_0.5)?xBa]Zr_1?yTi_yO₃ ceramics (x = 0.06, 0.085, 0.09, 0.1 and y = 0.97) have been prepared by solid-state hot-pressing sintering process. The obtained samples reveal perovskite structure. Structural, thermal expansion, heat capacity, ferroelectric and dielectric measurements have been carried out on these samples in a wide temperature range. The broad anomalies were observed in thermal expansion and heat capacity, which approximately correspond to a structural, ferroelectric and dielectric properties anomaly. These anomalies can be related to temperature features of polar regions and a formation of long-range-order ferroelectric phase. The determined Burns temperature was found to increase with increasing Ba content. The obtained results are discussed in terms of local electric and strain fields caused by a difference in the ionic radii of (Na,Bi) and Ba, and Ti and Zr ions. The NBT–BTZ system is expected to be a new promising candidate for lead-free electronic ceramics.     

Impedance spectroscopy and piezoresponse force microscopy analysis of lead-free (1 − x) K0.5Na0.5NbO3 − xLiNbO3 ceramics

(1 ? x) K_0.5Na_0.5NbO₃ ? xLiNbO₃ (where x = 0.0, 5.0, 5.5, 6.0, and 6.5 wt.%) (KNLN) perovskite structured ferroelectric ceramics were prepared by the solid-state reaction method. X-ray diffraction patterns indicate that single phase was formed for pure KNN while a small amount of second phase (K₆Li₄Nb₁₀O₃₀, ～3%) was present in LN doped KNN ceramics. Phase analysis indicated the change in the crystal structure from orthorhombic to tetragonal with increase in LN content. The electrical behavior of the ceramics was studied by impedance spectroscopy technique in the high temperature range. Impedance analysis was performed using an equivalent circuit model. The impedance response in pure KNN and KNLN ceramics could be deconvoluted into two contributions, associated with the bulk (grains) and the grain boundaries. Activation energies for conductivity were found to be strongly frequency dependent. The activation energy obtained from dielectric relaxation data was attributed to oxygen vacancies. From PFM we found that the composition with 6.5 wt.% LN displays stronger piezocontrast as compared to pure KNN implying an evidence of a pronounced piezoelectric coefficient.     

Dielectric,ferroelectric and piezoelectric properties of (1−x)[K0.5Na0.5NbO3]−x[LiSbO3] ceramics

Lead-free (1?x)[K_0.5Na_0.5NbO₃]?x[LiSbO₃] (x=0, 0.04, 0.05 and 0.06)/(KNN-LS) ceramics were prepared by conventional solid-state reaction route (CSSR). For dense morphology pure KNN ceramic was sintered at 1120 °C and LS modified KNN ceramics were sintered at 1080 °C for 4 h, respectively. The structural study at room temperature (RT) revealed the transformation of pure orthorhombic to tetragonal structure with the increase in LS content in KNN-LS ceramics. Temperature dependent dielectric study confirmed the increase of diffuse phase transition nature with the increase in LS content in KNN-LS ceramics. The presence of orthorhombic to tetragonal (T_O?T) polymorphic phase transition temperature (PPT) ～43 °C confirmed the presence of two ferroelectric (orthorhombic and tetragonal) phases in 0.95KNN-0.05LS ceramics at RT. 0.95KNN-0.05LS ceramics showed better ferroelectric and piezoelectric properties i.e., remnant polarization (P_r)～18.7 μC/cm², coercive field (E_c)～11.8 kV/cm, piezoelectric coefficient (d₃₃)～215 pC/N, coupling coefficient (k_p)～0.415 and remnant strain ～0.07% were obtained.