Microstructure,dielectric, and piezoelectric properties of Ce‐modified Na0.5Bi4.5Ti4O15 high temperature piezoceramics

The cerium modified sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) piezoelectric ceramics have been prepared by using the conventional mixed oxide method. X‐ray diffraction analysis revealed that the cerium modified NBT ceramics have a pure four‐layer Aurivillius phase structure. The piezoelectric activity of NBT ceramics was found significantly improved by the modification of cerium. The Curie temperature T_c, and piezoelectric coefficient d₃₃ for the NBT ceramics with 0.50 wt% cerium modification were found to be 655 °C, and 28 pC/N respectively. The Curie temperature gradually decreased from 668 °C to 653 °C with the increase of cerium modification. The dielectric spectroscopy showed that the samples possess stable piezoelectric properties, demonstrating practical potential that for high temperature applications. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dielectric and Piezoelectric Properties of Sodium Bismuth Titanate Ceramics with KCe Substitution

The piezoelectric properties of the (KCe)-substituted sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) piezoelectric ceramics are investigated. The piezoelectric properties of NBT ceramics are significantly enhanced by (KCe) substitution. The Curie temperature Tc, and piezoelectric coefficient d₃₃ for the (KCe)-substituted NBT are found to be 663ºC, and 27pC/N, respectively. Dielectric and annealing spectroscopy resent that the (KCe) co-substituted NBT piezoelectric ceramics possess stable piezoelectric properties.     

The effect of CuO and NiO doping on dielectric and ferroelectric properties of Na0.5Bi0.5TiO3 lead-free ceramics

In the present work, lead-free piezoelectric ceramics (Na_0.5Bi_0.5)TiO₃ –xCuO–yNiO (for x = 0.0, 0.02, 0.04 and 0.06) have been prepared by a conventional solid-state reaction method. An investigation of CuO and NiO doping in bismuth sodium titanate (BNT) and a study of the structure, morphology, and dielectric and ferroelectric properties of the NBT–CuNi system have been conducted. Phase and microstructural analysis of the (Na_0.5Bi_0.5)TiO₃ (NBT) based ceramics has been carried out using X-ray diffraction and scanning electron microscopy (SEM) techniques. Field emission scanning electron microscopy (FE-SEM) images showed that inhibition of grain growth takes place with increasing Cu and Ni concentration. The results indicate that the co-doping of NiO and CuO is effective in improving the dielectric and ferroelectric properties of NBT ceramics. Temperature-dependent dielectric studies have also been carried out at room temperature to 400 °C at different frequencies. The NBT ceramics co-doped with x = 0.06 and y = 0.06 exhibited an excellent dielectric constant ?_r = 1514. The study suggests that there is enormous scope of application of such materials in the future for actuators, ultrasonic transducers and high-frequency piezoelectric devices.     

Lead‐free piezoelectric (Na0.5Bi0.5)0.94TiO3–Ba0.06TiO3 nanofiber by electrospinning

Lead‐free (Na_0.5Bi_0.5)_0.94TiO₃–Ba_0.06TiO₃ (NBT‐BT6) nanofibers were synthesized by the sol–gel process and electrospinning, and a butterfly‐shaped piezoelectric response was measured by scanning force microscopy. NBT‐BT6 nanofibers with perovskite phase were formed, after being cleaned at 700 °C for 1 hour, and the diameters are in the range of 150 nm to 300 nm. The average value of the effective piezoelectric coefficient d₃₃ is 102 pm/V. The high piezoelectricity may be attributed to the easiness for the electric field to tilt the polar vector of the domain and to the increase of the possible spontaneous polarization direction. There is a potential for the application of NBT‐BT6 nanofibers in nanoscale piezoelectric devices. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Piezoelectric and ferroelectric properties of [(K0.4725Na0.4725)Li0.055]NbO3–(Ag0.5Li0.5)TaO3 lead‐free ceramics

New lead‐free piezoelectric (1 – x)[(K_0.4725Na_0.4725)Li_0.055]NbO₃– x (Ag_0.5Li_0.5)TaO₃ [(1 – x)KNNL–x ALT] ceramics were prepared by conventional sintering. Piezoelectric and ferroelectric properties and Curie temperature of the ceramics were studied. The (1 – x)KNNL–x ALT (x = 0.04) ceramics exhibit good properties (d₃₃ ～ 252 pC/N, k_p ～ 41%, T_C ～ 471 °C, T_o–t = 47 °C, P_r = 33.1 μC/cm², E_c = 10.6 kV/cm). These results show that (1 – x)KNNL–x ALT (x = 0.04) ceramic is a promising lead‐free piezoelectric material for high temperature application. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Enhanced depolarization temperature in 0.90NBT–0.05KBT–0.05BT ceramics induced by BT nanowires

The depolarization temperature (T_d) of piezoelectric materials is an important figure of merit for their application at elevated temperatures. This study focuses on the effect of BaTiO₃ (BT) nanowires on T_d and piezoelectric properties of morphotropic-phase-boundary 0.90NBT–0.05KBT–0.05BT ceramics. The results reveal that BaTiO₃ nanowires can pin the domain wall, leading to the increase of coercive field (E_c) from 21.06 kV/cm to 34.99 kV/cm. The T_d value of 0.90NBT–0.05KBT–0.05BT ceramics can be enhanced approximately 20 °C when using BT nanowires instead of BT solution as the raw material. Meanwhile, at the same polarization conditions, the piezoelectric constant of the ceramic added BT nanowires (172 pC/N) is decreased but still remains a larger value compared with those of other lead-free ceramics. The results imply that the addition of BT nanowires into NBT–KBT is a very effective route to improve T_d.     

Microstructure,dielectric, and piezoelectric properties of 0.38Bi(Gax Sc1–x )O3–0.62PbTiO3 high temperature piezoelectric ceramics

0.38Bi(Ga_x Sc_1–x )O₃–0.62PbTiO₃ (BGSPTx) ceramics have been prepared by using the conventional mixed oxide method. X‐ray diffraction analysis revealed that BGSPTx has a pure perovskite structure, and the crystal symmetry of BGSPTx changed from rhombohedral to tetragonal with increasing Ga content (x). The Curie temperature (T_C) of BGSPTx ceramics is in the range of 448–467 °C for different x. The ferroelectric phase transition of BGSPTx was found to be of the first order type according to the Curie–Weiss law. For x = 0.125, BGSPTx ceramics show enhanced piezoelectric properties: piezoelectric constant d₃₃ = 420 pC/N and d₃₁ = –142 pC/N, planar and thickness electromechanical coupling factors k_p = 56.27% and k_t = 56.00%, respectively. The high‐T_C of BGSPTx coupled with its excellent piezoelectric properties suggests those future high‐temperature applications. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

New crystallographic dielectric phase boundary in K0.5Na0.5NbO3‐based lead‐free ceramics

0.979K_0.5Na_0.5Nb_1‐xSb_x O₃‐0.021Bi_0.5Na_0.5TiO₃ (KNNSx ‐BNT) lead‐free piezoelectric ceramics were fabricated by conventional solid state reaction technique, and their phase transition and electrical properties were studied. With the increase of x, the rhombohedral‐orthorhombic phase transition temperature of the ceramics increases. Finally, both the rhombohedral‐orthorhombic and orthorhombic‐tetragonal phase transitions of the ceramics were modified to be around room tempera‐ ture when about 6% Sb were substituted for the Nb site, resulting in the formation of a new phase boundary separating rhombohedral and tetragonal phases. The formation of the new phase boundary results in excellent properties for the ceramics, that is, the KNNS0.05‐BNT ceramic shows an enhancement in piezoelectric properties: d₃₃ = 380 pC/N and k_P = 0.438. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of lead free (K0.5Na0.5)NbO3-LiSbO3 piezoceramic

(K_0.5Na_0.5)NbO₃ (KNN) based lead free ceramics have been fabricated by a solid state reaction. In this work, LiSbO₃ (LS) modified KNN based ceramics were sintered at atmospheric pressure and high density (>96% theoretical) was obtained. The detailed elastic, dielectric, piezoelectric and electromechanical properties were characterized by using the resonance technique combined with the ultrasonic method. The full set of material constants for the obtained polycrystalline ceramics were determined and compared to the pure hot pressed KNN counterpart. KNN-LS polycrystalline ceramic was found to have higher elastic compliance, dielectric permittivity and piezoelectric strain coefficients, but lower mechanical quality factor, when compared to pure KNN, exhibiting a “softening” behavior. However, a high coercive field (∼17 kV/cm) was found for the LS modified KNN material. The properties as a function of temperature were determined in the range of −50-250 ^°C, showing a polymorphic phase transition near room temperature, giving rise to improved piezoelectric behavior.     

Piezoelectric properties of PbHfO3–PbTiO3–Pb(Mg1/3Nb2/3)O3 ternary ceramics

(1 – x)Pb(Hf_1–yTi_y)O₃–x Pb(Mg_1/3Nb_2/3)O₃ (x = 0.1 ～ 0.25, y = 0.555) ternary piezoelectric ceramics were prepared using the two‐step precursor method. Morphotropic phase boundary (MPB) compositions, located at x = 0.18 ～ 0.22, were confirmed using X‐ray diffraction and by their dielectric, piezoelectric and ferroelectric properties. The optimum dielectric and piezoelectric properties were achieved for the MPB composition 0.8Pb(Hf_0.445Ti_0.555)O₃–0.2Pb(Mg_1/3Nb_2/3)O₃, with dielectric permittivity ε_r, piezoelectric coefficient d₃₃, planar electromechanical coupling k_p and Curie temperature T_C being on the order of 2800, 680 pC/N, 70% and 276 °C, respectively. Of particular significance is that the new ternary ceramics exhibit comparable piezoelectric and electromechanical properties to commercial PZT5H ceramics, but with much improved T_C, showing a potential for applications at elevated temperature. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dielectric and piezoelectric properties of barium-modified Aurivillius-type Na0.5Bi4.5Ti4O15

In this study, monophasic Ba_x(Na_0.5Bi_0.5)_1−xBi₄Ti₄O₁₅ (x=0.03, 0.06, 0.09 and 0.12) ceramics fabricated from the powders synthesized via the solid-state reaction route exhibited relaxor behavior. X-ray diffraction analysis revealed that the barium-modified Na_0.5Bi_4.5Ti₄O₁₅ ceramics have a pure four-layer Aurivillius phase structure. Dielectric properties and phase transitions were studied and are explained in terms of lattice response of these ceramics. A shift in ferroelectric–paraelectric phase transition (T_c) to lower temperatures and a corresponding increase in permittivity peak with increasing concentration of Ba²⁺ are also observed. The decrease of orthorhombicity in the lattice structure by the larger Ba²⁺ ion incorporation, indicating an approach of a and b parameters, results in lower Curie temperature. The piezoelectric activity of Na_0.5Bi_4.5Ti₄O₁₅ (NBT) ceramics was significantly improved by the modification of barium. The Curie temperature T_c and piezoelectric coefficient d₃₃ for the composition with x=0.12 were found to be 635 °C and 21 pC/N, respectively. The relationship of polarization with lattice response is discussed.     

Combined effects of Li content and sintering temperature on?polymorphic phase boundary and electrical properties of Li/Ta co-doped (Na, K)NbO3 lead-free piezoceramics

Crystallographic structure, phase transition and electrical properties of lead-free (Na_0.535K_0.485)_1−x Li _x (Nb_0.942Ta_0.058)O₃ (x=0.042–0.098) (NKL _x NT) piezoelectric ceramics were investigated. The experimental results show that both Li content and sintering temperature strongly affect the orthorhombic–tetragonal polymorphic phase boundary (PPB), which results in remarkable differences of the piezoelectric property and its temperature stability in the NKL _x NT ceramics. Chemical analysis indicates that sodium volatilizes more seriously than potassium and lithium with increasing sintering temperature. Due to the comprehensively optimized effects of Li content and sintering temperature, an enhanced piezoelectric constant d ₃₃ (276 pC/N) was obtained at room temperature in the ceramics with x=0.074 sintered at 1000°C. In the same composition, a further high d ₃₃ up to 354 pC/N was obtained at 43°C, which is close to its T _o−t temperature. Furthermore, better temperature stability can be obtained when x=0.082 sintered at 1000°C, whose piezoelectric constant d ₃₃ (236 pC/N) keeps almost constant from room temperature to 100°C. Such a temperature-independent piezoelectric property is available in the NKL _x NT ceramics with high Li content because its T _o−t was moved below room temperature.     

Effects of (LiCe) co-substitution on the structural and electrical properties of CaBi2Nb2O9 ceramics

The piezoelectric, dielectric, and ferroelectric properties of the (LiCe) co-substituted calcium bismuth niobate (CaBi₂Nb₂O₉, CBNO) are investigated. The piezoelectric properties of CBNO ceramics are significantly enhanced and the dielectric loss tanδ decreased. This makes poling using (LiCe) co-substitution easier. The ceramics (where □ represents A-site Ca²⁺ vacancies, possess a pure layered structure phase and no other phases can be found. The Ca_0.88(LiCe)_0.04□_0.04Bi₂Nb₂O₉ ceramics possess optimal piezoelectric properties, with piezoelectric coefficient (d₃₃) and Curie temperature (T_C) found to be 13.3 pC/N and 960 ℃, respectively. The dielectric and piezoelectric properties of the (LiCe) co-substituted CBNO ceramics exhibit very stable temperature behaviours. This demonstrates that the CBNO ceramics are a promising candidate for ultrahigh temperature applications.     

Evolution of structural and electrical properties of (K,Na,Li)(Nb,Ta,Sb)O3 lead-free piezoceramics through CoO doping

Doping with transition metals is widely used for piezoceramic improvement. In this work, we study the effects of cobalt doping on the properties of the well known (K,Na,Li)(Nb,Ta,Sb)O₃ piezoelectric ceramics. Two different situations were observed: for low concentrations, Co²⁺ cations occupy the A-site of the perovskite structure, whereas for high concentrations they occupy the B-site. The piezoelectric properties of the material are slightly affected with the cobalt concentration, whereas the mechanical quality factor increases by a factor of nearly three.     

Pyroelectric properties of BiFeO3 ceramics prepared by a modified solid-state-reaction method

BiFeO₃ (BFO) ceramics were prepared by a modified solid-state-reaction method which adopts a higher heating/cooling rate during the sintering process than usually used. It was found that the calcination temperature T _cal (from 400 to 750°C) does not influence the BFO phase formation, while the sintering temperature T _sin (from 815 to 845°C) dominates the phase purity. The optimum sintering temperature was in the range from 825 to 835°C. The optimized samples exhibit saturated ferroelectric hysteresis loops with a remnant polarization of 13.2 μC/cm². The measured piezoelectric coefficient d ₃₃ was 45 pC/N. No remnant magnetization was observed in all of the samples. The pyroelectric properties were studied as a function of temperature and frequency. A pyroelectric coefficient as high as 90 μC/m² K was obtained at room temperature in the optimized sample. An abrupt decrease of the pyroelectric coefficient was observed at temperatures between 70 and 80°C. On the basis of our results, BFO may have the potential for pyroelectric applications.     

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.     

Non-interferometric transient quantitative phase microscopy for ultrafast engineering

Lead-free piezoelectric ceramics Bi_0.5(Na_1-x-yK_xAg_y)_0.5TiO₃ [BNKAT(x/y)] have been synthesized by the mixed oxide method. The effects of the amount of K⁺ and Ag⁺ on the electrical properties were examined. X-ray diffraction patterns indicate that K⁺ and Ag⁺ ions partially substitute for the Na⁺ ions in Bi_0.5Na_0.5TiO₃ and form a solid solution during sintering. At room temperature, the ceramics exhibit good performances with piezoelectric constant d₃₃=189 pC/N, electromechanical coupling factor k_p=35.0%, remanent polarization P_r=39.5 μC/cm², and coercive field E_c=3.3 kV/mm, respectively. The curves of the dielectric constant ε_r and loss tangent tan δ versus temperature show that the transition temperature from ferroelectric to anti-ferroelectric phase decreases with increasing the K⁺ content for the compositions researched. The dependencies of k_p and polarization versus electric (P–E) hysteresis loops on temperature reveal that the depolarization temperature T_d of BNKAT(0.15/0.015) ceramics, which have good piezoelectric properties (d₃₃=134 pC/N, k_p=32.5%) and strong ferroelectricity (P_r=39.5 μC/cm², E_c=4.1 kV/mm) at room temperature, is above 160 °C. PACS 77.22.-d; 77.65.Bn; 77.80.Bh; 77.80.Dj; 77.84.Dy     

Structure, electrical properties and temperature characteristics of?Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–Bi0.5Li0.5TiO3 lead-free piezoelectric ceramics

(1−x−y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃– yBi_0.5Li_0.5TiO₃ lead-free piezoelectric ceramics have been prepared by an ordinary sintering technique, and their structure, electrical properties, and temperature characteristics have been studied systematically. The ceramics can be well-sintered at 1050–1150 °C. The increase in K⁺ concentration decreases the grain-growth rate and promotes the formation of grains with a cubic shape, while the addition of Li⁺ decreases greatly the sintering temperature and assists in the densification of BNT-based ceramics. The results of XRD diffraction show that K⁺ and Li⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a solid solution with a pure perovskite structure. As x increases from 0.05 to 0.50, the ceramics transform gradually from rhombohedral phase to tetragonal phase and consequently a morphotropic phase boundary (MPB) is formed at 0.15≤x≤0.25. The concentration y of Li⁺ has no obvious influence on the crystal structure of the ceramics. Compared with pure Bi_0.5Na_0.5TiO₃, the partial substitution of K⁺ and Li⁺ for Na⁺ lowers greatly the coercive field E _c and increases the remanent polarization P _r of the ceramics. Because of the MPB, lower E _c and large P _r, the piezoelectricity of the ceramics is improved significantly. For the ceramics with the compositions near the MPB (x=0.15–0.25 and y=0.05–0.10), the piezoelectric properties become optimum: piezoelectric coefficient d ₃₃=147–231 pC/N and planar electromechanical coupling factor k _P=20.2–41.0%. In addition, the ceramics exhibit relaxor characteristic, which probably results from the cation disordering in the 12-fold coordination sites. The depolarization temperature T _d shows a strong dependence on the concentration x of K⁺ and reaches the lowest values at the MPB. The temperature dependences of the ferroelectric and dielectric properties at high temperatures may imply that the ceramics may contain both the polar and non-polar regions at temperatures above T _d.     

Growth and properties of Li,Ta modified (K,Na)NbO3 lead‐free piezoelectric single crystals

Li, Ta modified (K,Na)NbO₃ single crystals with the size of 18 mm × 18 mm × 10 mm were successfully grown by top‐seeded solution growth method, with orthorhombic–tetra‐gonal phase transition temperature ～79 °C and Curie temperature ～276 °C. The electromechanical coupling factors k₃₃ and k_t were found to be ～88% and ～65%, respectively. The piezoelectric coefficient d₃₃ for the [001]_c poled crystals reached 255 pC/N. In addition, the electromechanical coupling factor exhibited high stability over the temperature range of –50 °C to 70 °C, making these lead free crystals good candidates for electromechanical applications. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of SrTiO3 on dielectric and piezoelectric properties of NBT

Composites of (1 ? x)Na_0.5Bi_0.5TiO₃-(x)SrTiO₃, where x = 0.05, 0.10, 0.15, 0.2, 0.3 and 0.9 are studied. Individual compounds are synthesized by sol gel, and composites are prepared by solid-state sintering process. Through the analysis of X-ray diffraction, lattice parameters are obtained and, from scanning electron microscope (SEM), micro-structure of the samples is observed. The depolarization temperature (T_d) and the Curie temperature (T_c) are determined from dielectric studies. Relaxor behavior of the samples is interpreted using modified Curie Weiss law. Control of polarization in sodium bismuth titanate (NBT) is achieved using strontium titanate (SrTiO₃-ST) and studied through polarization vs. electric field (PE) loops and piezoelectric measurements. The intra-granual and inter-granual effects on the electrical properties of the ceramics are studied from impedance analysis.