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 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.     

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.     

Piezoelectric activity and phase transitions in (PMN)0.69(PT)0.31 single crystal

Piezoelectric and dielectric investigations have been performed on a (PMN)_0.69(PT)_0.31 single crystal. Low frequency (100?Hz) dielectric permittivity measurements revealed distinct anomaly at 129°C (T _εmax) corresponding to the structural transformation from the tetragonal to cubic phase. Two other anomalies have been detected at 90 and 96°C. After preliminary polarization in the d.c. electric field, switched on above T _εmax and switched off inside the tetragonal phase, the piezoelectric activity has been observed in function of temperature. Values of the piezoelectric resonance frequencies changed markedly at 96°C (on cooling) and 124°C (on heating) showing clear softening of the elastic properties near these temperatures. Values of the piezoelectric and electromechanical coupling coefficients obtained were respectively of the order of 800?pCN^?1 (d ₃₁) and 0.35?(k ₃₁). Piezoelectric activity was detected tens of degrees above the temperature T _εmax and disappeared at temperature at which the dispersion of the dielectric permittivity due to the presence of polar nanoregions is negligible. It was found that strong softening of the elastic properties accompanies phase transitions to the tetragonal and monoclinic phase.     

The piezoelectric effect in Pb[(Fe1/3Sb2/3) x Ti y Zr z ]O3 ceramics

The piezoelectric properties of Pb[(Fe_1/3Sb_2/3) _x Ti _y Zr _z ]O₃ with x + y + z = 1, x = 0.1, y = 0.43–0.48 ceramics have been investigated over a broad temperature range using a resonance technique. The influence of modification of PZT normal ferroelectric synthesized near the morphotropic phase boundary by a relaxor Pb(Fe_1/3Sb_2/3)O₃ compound on its physical properties was studied. The coefficients s ₁₁, k ₃₁, and d ₃₁ were calculated from the parameters characterizing the behavior of damped harmonic oscillator in the vicinity of the piezoelectric resonance. Several anomalies of the piezoelectric coefficients have been found in the temperature range 300–600 K. Two diffuse phase transitions were observed in Pb[(Fe_1/3Sb_2/3) _x Ti _y Zr _z ]O₃. The anomaly near 530 K for y = 0.43 is responsible for the transition from the rhombohedral phase to the tetragonal one. For y > 0.44 this transition is found to be very diffuse and the coexistence of rhombohedral and tetragonal phases occurs. The observation of low piezoelectric activity confirms the existence of polar regions in Pb[(Fe_1/3Sb_2/3) _x Ti _y Zr _z ]O₃ above T _m.     

Optical and piezoelectric anomalies of ordered (Sc,Ga) N and (Sc,In) N ternaries

Theoretical results are presented regarding the incorporation of Scandium into wurtzite GaN and InN binaries. The electric, optical and piezoelectric properties of the resulting ScGaN and ScInN systems are reported by using first-principles Local-density approximation (LDA) within density functional theory (DFT), Berry phase approach within modern theory of polarization and phonon calculations within the density functional perturbation theory. Our results predict the existence of breaking-symmetry structural phase transition in ordered Sc_0.5Ga_0.5N and Sc_0.5In_0.5N alloys when subjected to a compressive or tensile strain. Moreover, our results demonstrate the existence of symmetry preserving pressure-induced isostructural phase transitions in ordered ScGaN and ScInN systems for different Sc concentrations. It has been shown that the existence of isostructural phase transitions leads to dramatic changes in optical, acoustic, and piezoelectric properties of ordered ScGaN and ScInN systems under high pressure. In particular, this study demonstrates that the existence of first-order isostructural phase transitions in Sc₁Ga₁N₂ at a critical hydrostatic pressure of 12.3 GPa leads to a huge enhancement of piezoelectricity (i.e., the e ₃₃ piezoelectric coefficient adopts a huge value as large as 13 C/m²). In addition, It has been shown that ordered Sc_0.5Ga_0.5N and Sc_0.5In_0.5N alloys exhibit tremendous piezoelectric response, associated with a breaking-symmetry phase transition from nonpolar P6₃/mcc(D_6h) space group to a polar P6₃ mc(C_6v) structure, at fixed Ga, In and Sc compositions, as a function of the in-plane compressive and tensile strains. We also reveal the reason behind, and consequences of, these unusual properties associated with the strain-induced and pressure-induced structural phase transitions in the novel ScGaN and ScInN ordered structures.     

Microstructure and piezoelectric properties of Bi0.5(Na0.82K0.18)0.5TiO3−NaSbO3 ceramics

Lead-free piezoelectric ceramics (1−x)Bi_0.5(Na_0.82K_0.18)_0.5TiO₃−xNaSbO₃ have been prepared by a conventional ceramics technique, and their microstructure and electrical properties have been investigated. The addition of NaSbO₃ has no remarkable effect on the crystal structure within the studied doping content; however, an obvious change in microstructure took place. With increase in NaSbO₃ content, the temperature from a ferroelectric to antiferroelectric phase transition increases, and the temperature for a transition from antiferroelectric phases to paraelectric phases changes insignificantly. Simultaneously, the temperature range between the rhombohedral phase transition point and the Curie temperature point becomes smaller. The piezoelectric properties significantly increase with increase in NaSbO₃ content and the piezoelectric constant and electromechanical coupling factor attain maximum values of d₃₃=160 pC/N and k_p=0.333 at x=0.01. The results indicate that (1−x)Bi_0.5(Na_0.82K_0.18)_0.5TiO₃−xNaSbO₃ ceramic is a promising lead-free piezoelectric candidate material.     

Piezoelectric composites with a high stability of the piezoelectric modulus under the action of mechanical and temperature fields

New technologies have been proposed for increasing the stability of the piezoelectric modulus d _ij of “polymer-ferroelectric/piezoelectric ceramic” composites under the action of mechanical stresses and temperatures. It has been shown that a decrease in the electronegativity of cations or in the covalency of cation-oxygen bonds of the piezoelectric phase, as well as the cyclic electric and thermal polarization and the crystallization under the action of an electric discharge plasma, leads to an increase in the stability of the piezoelectric modulus of polymer-piezoelectric ceramic composites under the mechanical and temperature actions. A possible mechanism has been proposed underlying the effect of an increase in the stability range of the piezoelectric modulus d _ij due to the crystallization under the action of the electric discharge plasma, the decrease in the covalency of cation-oxygen bonds of the piezoelectric phase, and the cyclic electric and thermal polarization of piezoelectric composites.     

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.     

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)     

Ionic conduction and effect of immobile cation substitution in binary system (AgI)4/5–(PbI2)1/5

Samples of stoichiometry (AgI)₄(PbI₂)_1?x (CdI₂) _x , (0 ≤ x ≤ 0.4), have been prepared and studied by electrical conductivity, X-ray powder diffraction and DSC techniques. The ionic conductivity of samples was found to increase with temperature, and an abrupt increase at phase transition temperature was observed. The Cd⁺²-doped samples exhibited lower phase transition temperature compared to that of the pure samples. The ionic conductivity decreases with an increase in Cd⁺² content in pre-transition, while enhances in conductivity result in Cd⁺² content samples of x ≤ 0.2 in the post-transition region. Different resources of investigation confirmed the solubility limit of Cd⁺² in the high-temperature phase to be x = 0.2. The change in the ionic conductivity of Cd⁺²-doped samples is explained by the increase in the defect concentration and the free volume available in the lattice. The drop in phase transition temperature of Cd²⁺-doped systems is attributed to the lattice distortion and the increase in the defect–defect interaction.     

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.     

Effect of Zn–Ti double substitution on the electrical properties of Bi4V2O11

New samples of the Bi₂Zn_0.1–xTi_xV_0.9O_5.35+x; 0.02 ≤ x ≤ 0.08 system have been synthesized through a standard solid-state reaction route. XRD analysis and differential thermal analysis have been used to characterize the phase structure of samples. The γ′ phase is stabilized to room temperature in all investigated samples. The electrical properties of the BIZNTIVOX system have been studied by using AC impedance spectroscopy. An AC impedance response as a function of frequency (20 Hz–1 MHz) has been used to investigate the electrical conductivity and the dielectric permittivity in the temperature range of 150 °C–700 °C. In this temperature range, the phase transition γ′ to γ has been observed in all the compositions studied. AC impedance spectroscopy indicates that the resistance of samples decreases with increase of temperature. The ionic conductivity of samples appeared as a two-line region in Arrhenius dependence. At 300 °C, the highest ionic conductivity is shown by the composition x = 0.05 (σ₃₀₀ = 1.35 × 10^?4 S cm^?1).     

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)     

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)     

锰掺杂对Ba(Zr,Ti)O3陶瓷压电与介电性能的影响

采用氧化物固相反应法制备了锰掺杂改性的Ba(Zr_0.06Ti_0.94)O₃陶瓷.研究了锰的掺杂量对Ba(Zr_0.06Ti_0.94)Mn_xO₃ (BZTM)陶瓷的结构、介电和压电性能的影响.实验发现,当锰含量x<0.5 mol%时进入晶格,使材料压电性能提高,损耗减小,表现出受主掺杂的特性;当锰含量x>0.5 mo 关键词： Ba(Zr 3 陶瓷')" href="#">Ti)O₃ 陶瓷 锰掺杂 介电性能 压电性能     

磁电双层膜层间耦合的弹性力学研究

基于磁致伸缩相与压电相的本构方程,应用弹性力学模型,简要介绍了如何推导自由状态的磁电双层膜纵向、横向磁电(ME)电压系数. 并采用相应的材料参数计算了La_07Sr_03MnO₃-Pb(Zr,Ti)O₃ (LSMO-PZT),Tb_1-xDy_xFe_2-y(TDF)-PZT双层膜中的磁电电压系数,具体分析了其与压电相 关键词： 磁电效应 双层膜 TDF LSMO PZT     

Bipolar cycling effects in BiFeO3–BaTiO3 piezoelectric ceramics

BiFeO₃–BaTiO₃ (BF-BT) lead-free piezoelectric system has been paid much attention due to good piezoelectric properties and high Curie temperature. Poling is a process to align ferroelectric domains and increase the piezoelectric coefficients. During the poling process, unipolar direct current (dc) electric fields were applied conventionally, but recently bipolar alternating current (ac) cycling was reported to improve piezoelectric properties in rhombohedral structure piezoelectric materials. We investigated the effects of dc-poling and ac-cycling in BF-BT ceramics. The d₃₃ increased from 210 pC/N with dc-poling to 240 pC/N with ac-cycling in the morphotropic phase boundary region of BF-BT with domain engineering. This improvement of piezoelectric properties with ac-cycling was consistent with the structural evolution related to ferroelectric domains.     

Structural, dielectric relaxation and piezoelectric characterization of Sr substituted modified PMS-PZT ceramic

Pyrochlore phase free [Pb_0.94Sr_0.06] [(Mn_1/3Sb_2/3)_0.05(Zr_0.53Ti_0.47)_0.95] O₃ ceramics has been synthesized with pure Perovskite phase by semi-wet route using the columbite precursor method. The field dependences of the dielectric response and the conductivity have been measured in a frequency range from 50 Hz to 1 MHz and in a temperature range from 303 K to 773 K. An analysis of the real and imaginary parts of the dielectric permittivity with frequency has been performed, assuming a distribution of relaxation times. The scaling behavior of the dielectric loss spectra suggests that the distribution of the relaxation times is temperature independent. The SEM photographs of the sintered specimens present the homogenous structures and well-grown grains with a sharp grain boundary. The material exhibits tetragonal structure. When measured at frequency (100 Hz), the polarization shows a strong field dependence. Different piezoelectric figures of merit (k_p, d₃₃ and Q_m) of the material have also been measured obtaining their values as 0.53, 271 pC/N and 1115, respectively, which are even higher than those of pure PZT with morphotropic phase boundary (MPB) composition. Thus the present ceramics have the optimal overall performance and are promising candidates for the various high power piezoelectric applications.     

Effect of Polarization Temperature on the Chain Segment Motion and Space Charge Detrapping in Polyamide 610 Film Electrets

The effect of polarization temperature on the chain segment motion and charge trapping and detrapping in polyamide 610 films has been investigated by means of thermally stimulated depolarization current (TSDC) and wide-angle X-ray diffraction (WAXD). A small part of the amorphous phase of quenched polyamide 610 changes into the crystalline state with increasing polarization temperature. There are three current peaks (named α, ρ₁, and ρ₂ peak, respectively) in the TSDC spectra. The α peak corresponds to the glass transition, the ρ ₁ peak is attributed to space charge trapped in the amorphous phase, and interphase between crystalline and amorphous phases, and the ρ ₂ peak originates from space charge trapped in the crystalline phase. By analyzing the characteristic parameters of these peaks, it was found that the increase of polarization temperature induced a decrease of the chain segment mobility and promoted the creation of structural traps in polyamide 610. The decrease of the chain segment mobility in the amorphous phase made the intensity of the α peak weak and the activation energy increased. The higher the polarization temperature, the higher the degree of crystallinity and the more charge carriers trapped in the crystalline phase. So, the increase of polarization temperature made the intensity of the ρ ₂ peak strong and increased the stability of trapped charge in the crystalline phase. The increase of polarization temperature also made the intensity of the ρ ₁ peak strong and decreased the stability of trapped charge in the amorphous phase and interphase.