Influence of MoO3 on electrical and microstructural properties of (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3

Microstructure, piezoelectric properties and dielectric behavior of undoped and MoO₃-doped lead-free (K_0.44Na_0.52Li_0.04)(Nb_0.86?xTa_0.10?xSb_0.04?x)Mo_5/6xO₃ were investigated. Samples were obtained by the conventional solid state reaction. X-ray diffraction (XRD) and Raman spectra revealed the formation of a perovskite phase, together with some minor secondary phase which could be assigned by XRD to K₃LiNb₆O₁₇. XRD also showed that the perovskite evolved from a tetragonal to orthorhombic symmetry with the increased doping level. The temperature dependence on real permittivity revealed the presence of a diffuse phase transition. This behavior raised with MoO₃ concentration. Also, dielectric relaxation processes were observed at room temperature resulting dependent on doping level and sintering time.     

Lead-free vanadium-substituted (K0.485Na0.5Li0.015)(Nb0.9Ta0.1)O3 piezoceramics synthesized from nanopowders

Lead-free, alkaline niobate-based piezoelectric ceramics substituted with vanadium (K_0.485Na_0.5Li_0.015)(Nb_0.9?x Ta_0.1V _x )O₃ (x = 0, 0.05, 0.10, 0.15 and 0.2) were synthesized from nanocrystalline powders by traditional solid state sintering technique. The base composition chosen is among those recently reported to show high piezoelectric properties. The nanocrystalline powders were produced by high energy ball milling. The crystalline phase of all the ceramics prepared was found to be perovskite with orthorhombic symmetry. Without any sintering aid, the bulk density of 97 % of the theoretical density was obtained for the ceramics with no vanadium. The optimum sintering temperature for all compositions was achieved at a low value of 1,050 °C. In the composition range studied, increasing V⁵⁺ content in the ceramics gives rise to a gradual decrease in room temperature dielectric constant (ε _r ) from 1,193 to 474, remnant polarization (P _r ) from 12.9 to 5.6 μC/cm², electromechanical coupling factor (k _p ) from 0.45 to 0.32, and piezoelectric charge constant (d ₃₃) from 156 to 53 pC/N. The decrease in these parameters is attributed to the associated decrease in density and grain size of the ceramics with increasing V⁵⁺ content. Increasing V⁵⁺ content from 0 to 0.15 results in an increase in the coercive field from 9.9 to 15.5 kV/cm, thereby, making the ceramics harder in this range of composition.     

Microstructure and piezoelectric properties of NaF-doped K0.5Na0.5Nb0.95Ta0.05O3 lead-free ceramics

The effects of NaF on the microstructure and electrical properties of K_0.5Na_0.5Nb_0.95Ta_0.05 lead-free ceramics prepared by conventional sintering method were investigated in this study. The dopant NaF effectively lowers the sintering temperature and promotes the grain growth. Samples with a high relative density up to 96.3 % are achieved by adding 0.6 wt% NaF to improve the sinterability. The electric properties are also enhanced, and the optimum properties are achieved at the doping content of 1.0 wt% (d ₃₃ = 153 pC/N, k _P = 32.2 %, Q _m = 80.5, E _c = 0.89 kV/mm, and P _r = 16.5 μC/cm²). The improvement of ferroelectric and piezoelectric properties is suggested to be largely contributed to the compensation of sodium element from dopant NaF for the volatilization of A-site alkali elements.     

Structural and piezoelectric properties of barium-modified lead-free (K0.455Li0.045Na0.5)(Nb0.9Ta0.1)O3 ceramics

Ferroelectric (K_0.455Li_0.045Na_0.5)(Nb_0.9Ta_0.1)O₃ + x mol% BaCO₃ ceramic compositions with Ba²⁺ as an A-site dopant in the range of x = 0–1.2 mol% were synthesized by conventional ceramic processing route. Effect of Ba²⁺ content on the microstructure, ferroelectric, dielectric, and piezoelectric properties of the ceramics was investigated. The results of X-ray diffraction reveal that Ba²⁺ diffuse into the (K_0.455Li_0.045Na_0.5)(Nb_0.9Ta_0.1)O₃ lattices to form a solid solution with a perovskite structure having typical orthorhombic symmetry. As Ba²⁺ content increases, cell volume and tetragonality increase in the crystal structure of the ceramics. Increasing doping level of Ba²⁺ inhibits grain growth in the ceramics and reduces both the Curie temperature (T _c) and tetragonal–orthorhombic phase transition temperature (T _o-t). The bulk density, remnant polarization P _r, room-temperature dielectric constant (ε′_RT), planar electromechanical coupling factor k _p , and piezoelectric charge coefficient d ₃₃ are found to increase as Ba²⁺ concentration increases from 0 to 0.8 mol% and then decrease as Ba²⁺ content increases further from 0.8 to 1.2 mol%. High piezoelectric properties of d ₃₃ = 187 pC/N and k _p  = 48 % are found in 0.8 mol% Ba²⁺ composition. Optimum amount of Ba²⁺ dopant takes the polymorphic phase boundary region consisting of orthorhombic and tetragonal crystal structures of the ceramic system near the room temperature and enhances its piezoelectric properties.     

Dielectric and piezoelectric properties of CeO2-added nonstoichiometric (Na0.5K0.5)0.97(Nb0.96Sb0.04)O3 ceramics for piezoelectric energy harvesting device applications

In this study, nonstoichiometric (Na(0.5)K(0.5))(0.97)(Nb(0.96)Sb(0.04))O(3) ceramics were fabricated and their dielectric and piezoelectric properties were investigated according to the CeO(2) addition. In this ceramic composition, CeO(2) addition improved sinterability, electromechanical coupling factor k(p), mechanical quality factor Q(m), piezoelectric constant d(33), and g(33). At the sintering temperature of 1100°C, for the 0.2wt% CeO(2) added specimen, the optimum values of density = 4.359 g/cm(3), k(p) = 0.443, Q(m) = 588, ε(r) = 444, d(33) = 159 pC/N, and g(33) = 35 × 10(-3) V·m/N, were obtained. A piezoelectric energy harvesting device using 0.2 wt% CeO(2)- added lead-free (K(0.5)Na(0.5))(0.97)(Nb(0.96)Sb(0.04))O(3) ceramics and a rectifying circuit for energy harvesting were fabricated and their electrical characteristics were investigated. Under an external vibration acceleration of 0.7 g, when the mass, the frequency of vibration generator, and matching load resistance were 2.4 g, 70 Hz, and 721 Ω, respectively, output voltage and power of piezoelectric harvesting device indicated the optimum values of 24.6 mV(rms) and 0.839 μW, respectively-suitable for application as the electric power source of a ubiquitous sensor network (USN) sensor node.     

Effects of interstitial Li+ ions on the properties of novel Li4.08Zn0.04Si0.96O4 ceramic electrolyte

The aim of this work was to investigate the effects of interstitial ions in the novel Li_4 + 2xZn_xSi_1 − xO₄ (x = 0.04) compound prepared via sol gel method. The compound was indexed to the monoclinic unit cell in the space group P2_1/m and the chemical composition of the compound was very close to the designed composition. The introduction of two interstitial Li⁺ ions increased charge carrier concentration in the doped system resulting in an enhancement of conductivity by an order of magnitude as compared to that of the parent compound, Li₄SiO₄. The compound of Li_4.08Zn_0.04Si_0.96O₄ exhibited total conductivity values of 2.51 × 10^− 5 S cm^− 1 at ambient temperature and 3.01 × 10^− 3 S cm^− 1 at 500 °C. Ionic transference number corresponding to Li⁺ ion transport was also found to be higher than the value obtained for the parent compound. This proved that interstitial Li⁺ ions contributed to the total conductivity in the sample. Linear sweep voltammetry result showed that the Li_4.08Zn_0.04Si_0.96O₄ ceramic electrolyte was electrochemically stable up to 5.80 V versus a Li/Li⁺ reference electrode.     

高性能(Na0.51K0.44Li0.05)Nb0.92Ta0.08O3-Na5.4Cu1.3Sb10O29无铅压电陶瓷

采用传统的氧化物固溶工艺制备了（Na0.51K0.44Li0.05）Nb092Ta0.08O3和助烧剂Na5.4Cu13Sb10O29.对（Na0.51K044Li0.05）Nb0.92Ta0.08O3添加助烧剂Na5.4Cu1.3Sb10O29的研究表明,助烧剂能大幅度提高（Na0.51K0.44Li0.05）Nb0.92Ta0.08O3的压电和机电耦合性能.质量百分比为4%Na5.4Cu1.3Sb10O29掺杂的（Na051K0.44Li0.05）Nb092Ta0.08O3具有高的压电应变常数（d33=266pC/N）,高的机电耦合系数kt（46.7%）、k33（63.7%）,较低的损耗（tanδ=1.8%）,和高的居里温度（391℃）.这些参数表明,Na5.4Cu1.3Sb10O29掺杂的（Na0.51K0.44Li0.05）Nb0.92Ta0.08O3是替代锆钛酸铅且具有很好的应用前景的无铅压电陶瓷.     

Correlation between the structure and the piezoelectric properties of lead-free (K,Na,Li)(Nb,Ta,Sb)O3 ceramics studied by XRD and Raman spectroscopy

This article reviews on the use of Raman spectroscopy for the study of (K,Na,Li)(Nb,Ta,Sb)O(3) lead-free piezoceramics. Currently, this material appears to be one of the most interesting and promising alternatives to the well-known PZT piezoelectric materials. In this work, we prepare piezoceramics with different stoichiometries and study their structural, ferroelectric, and piezoelectric properties. By using both Raman spectroscopy and X-ray diffraction, we establish a direct correlation between the structure and the properties. The results demonstrate that the wavenumber of the A(1g) vibration is proportional to the tetragonality, the remnant polarization, and the piezoelectric coefficients of these materials. Thus, Raman spectroscopy appears as a very useful technique for a fast evaluation of the crystalline structure and the ferroelectric/ piezoelectric properties.     

Ba0.04Bi0.48Na0.48TiO3-SrTiO3陶瓷微结构和储能性能

采用传统固相反应法制备了一种无铅储能铁电陶瓷(1-x)Ba0.04Bi0.48Na0.48TiO3-xSrTiO3 (x=0.27、0.28、0.30、0.32、0.34、0.36),研究了该陶瓷体系的微观结构、铁电、介电和电导率特征.所有陶瓷均形成了钙钛矿结构固溶体,晶粒尺寸均匀且致密.各陶瓷所得铁电曲线趋于双电滞回线,呈现反铁电特征,剩余极化强度较小,击穿强度高.当x=0.34时,可获得0.977J/cm3的较优储能值,陶瓷弥散程度高,表现为典型的弛豫特性.此含量对应低频下陶瓷的离子电导率为2.4×10-8 S/cm,电子电导率为6.02×10-13 S/cm,表明离子电导居于主导地位.     

Microstructure and dielectric and piezoelectric properties of PbFe0.5Nb0.5O3 ceramics modified with Li2CO3 and MnO2

Unmodified lead ferroniobate (PFN) and samples modified with 1 wt % Li₂CO₃ (PFNL) and 1 wt % MnO₂ (PFNM) have been prepared by solid-state reactions followed by sintering by a conventional ceramic processing technique. The modifiers have been shown to change the nature of the recrystallization sintering process, reduce the optimal sintering temperature of the material, increase its average grain size, stabilize its dielectric properties, and improve its piezoelectric performance. The observed effects are interpreted in terms of the crystal-chemical specifics of the modifiers and their location in the structure of the parent compound.     

Effect of ceramic powder particle size on the electrical properties of Li0.03Na0.97Ta0.05Nb0.95O3 ceramics

We compare the microstructure, electrical properties, and Raman spectra of ceramic samples of the Li_0.03Na_0.97Ta_0.05Nb_0.95O₃ ferroelectric solid solution prepared by a conventional ceramic processing technique using ceramic powders with different particle sizes. The Li_0.03Na_0.97Ta_0.05Nb_0.95O₃ solid solutions prepared from the powders of different particle sizes are shown to differ only slightly in average grain size, pore size, and porosity, but the particle size of the ceramic powder has a significant effect on their electrical properties. The difference in properties between the samples is due not so much to the difference in particle size between the parent ceramic powders as to the fact that the diffusion processes involved in solid-state synthesis may give rise to composition gradients, and grains that differ in size may differ in microstructure and composition.     

Properties of B-site non-stoichiometric (K0.5Na0.5)(Nb0.9Ta0.1)1+x O3 lead-free piezoelectric ceramics

The non-stoichiometric (K_0.5Na_0.5)(Nb_0.9Ta_0.1)_1+x O₃ (x = 0, ±0.005, ±0.010) [KN(NT)_1+x ] lead-free piezoelectric ceramics were prepared by normal sintering. The samples were characterized by X-ray diffraction and scanning electron microscopy. All the KN(NT)_1+x ceramics possess orthorhombic perovskite structure. The grain growth of the ceramics is inhibited and the relative density is improved with increasing x. 0.5 mol% (NT)⁵⁺ excess KN(NT)_1+x ceramic which sintered at 1,120 °C has the highest piezoelectric performances among with other samples. Meanwhile, the (NT)⁵⁺ excess ceramics have better time stability than the (NT)⁵⁺ deficient ones. These results show that the KN(NT)_1+x ceramic with x = 0.005 is a promising lead-free piezoelectric material.     

Influence of Bi2O3 addition on structure and dielectric properties of Ag(Nb0.8Ta0.2)O3 ceramics

The structure and dielectric properties of perovskite Ag(Nb_0.8Ta_0.2)O₃ ceramics were explored. A small amount of Bi₂O₃ was used to modify the dielectric properties of the ceramics. The addition of Bi₂O₃ led the ceramics to a high densification and optimal dielectric properties. With the addition of 4.5 wt% Bi₂O₃, the permittivity of Ag(Nb_0.8Ta_0.2)O₃ ceramics increased from 470 to 733, the dielectric loss decreased from 62×10^?4 to 6.7×10^?4, and the temperature coefficient of capacitance, TCC, decreased from 2004 ppm/°C to ?50 ppm/°C. The high permittivity obtained was due to the high densification and weak Ta-O or Nb-O bond strength in the oxygen octahedron that results from the addition of Bi₂O₃.     

Lithium ion conductivity and mobility in the Li0.12Na0.88Ta0.4Nb0.6O3 solid solution

Lithium ion mobility and the superionic phase transition in the Li_0.12Na_0.88Ta_0.4Nb_0.6O₃ solid solution have been studied using temperature-dependent ionic conductivity measurements and Raman spectroscopy. From the temperature dependences of the conductivity and the width of a Raman line corresponding to Li⁺ and Na⁺ vibrations in the AO _x (A = Na⁺, Li⁺) polyhedra, the average lifetime of the Li⁺ ion in its equilibrium position and the height of the barrier to hopping have been estimated at ?3.9 × 10^?13 s and ?16 kJ/mol, respectively.     

Effects of La occupation site on the dielectric and piezoelectric properties of [Bi0.5(Na0.75K0.15Li0.10)0.5]TiO3 ceramics

The crystal structure, phase transition and ferroelectric (FE)/piezoelectric properties were investigated for three types of La-doped [Bi_0.5(Na_0.75K_0.15Li_0.10)_0.5]TiO₃ ceramics. The dielectric measurements showed that the transition between FE and antiferroelectric (AFE) phases near 180 °C became pronounced by La addition, and the maximum permittivity was observed at 360 °C in La-doped samples, whereas at 290 °C in non-doped samples. Normal FE and excellent piezoelectric properties were observed by P–E hysteresis loop and piezoelectric measurements in samples without vacancy. However, when the A-site or B-site vacancies were formed, the temperature range of AFE phase extended even appeared at room temperature, which resulted in the presence of deformed P–E curves and decrease of piezoelectric properties. It was suggested that the AFE phase originated from the decoupling effect between BO₆ octahedra in ABO₃ perovskites due to the A-site and/or B-site vacancies.     

Formation and microwave dielectric properties of Sr(Ga0.5Ta0.5)O3-based complex perovskites

The Sr(Ga0.5Ta0.5)O3-based perovskites with O2- and/or Sr2+ vacancies were formed by changing the A-site and/or B-site cation ratios. The Sr-deficient perovskites with a limited composition of Sr0.86(Ga0.36Ta0.64)O3 could be obtained, whereas oxygen vacancies were hardly created. The B′-site Ga3+ cation could be replaced with large Sc3+, In3+, Y3+, Nd3+ and La3+. The crystal symmetry of the complex perovskites changed from cubic (B′=Ga3+, Sc3+, In3+) to tetragonal (B′=La3+) through rhombohedral (B′=Y3+, Nd3+). The dielectric permittivities of these ceramics indicated no distinct dependence on the B′-site cation species. The temperature coefficient of permittivity might be associated with the symmetry change of the perovskite phases. Higher microwave Qf values, >Qf=38 000 GHz, were obtained for our complex perovskite ceramics, except with B′=La3+. This revised version was published online in July 2006 with corrections to the Cover Date.     

烧结方式对(K,Na,Li)(Nb,Sb,Ta)O3压电陶瓷的微观结构和物理性能的影响

(K,Na)NbO₃基陶瓷(KNLNST陶瓷)是一类很有发展潜力的无铅压电材料, 目前对其进行两步烧结相关的研究还很少。本工作分别采用普通烧结(Conventional Sintering, CS)和两步烧结(Two-step Sintering, TSS)制备了(K_0.4425Na_0.52Li_0.0375)(Nb_0.8825Sb_0.08Ta_0.0375)O₃陶瓷, 并进行微观结构与物性的对比研究。TSS可将(K,Na)NbO₃基陶瓷的相对密度ρ°由CS时的95.0%提高至97.0%, 压电系数d₃₃由CS时的363 pC/N增大到387 pC/N。两种烧结方式制备的KNLNST陶瓷的微观组织结构和电畴结构有着很大的差异。KNLNST-CS陶瓷的晶粒尺寸较小而且分布较为均匀, 极化后多数晶粒的电畴图案为简单的平行条纹。KNLNST-TSS陶瓷的晶粒尺寸则大小分布不均匀, 极化后许多大晶粒中呈现带状条纹内部又存在着精细的平行条纹的电畴图案。     

Ionic conductivity of Li x Na1 − x Ta y Nb1 − y O3 solid solutions

Experimental data demonstrate that Li _x Na_{1 ? y} Ta _y Nb_{1 ? y} O₃ (y ≠ 0) ferroelectric solid solutions near special concentration points (x = 0.125 and 0.25), which have increased degrees of short- and long-range order, undergo a superionic transition. In the Raman spectra of Li_0.12Na_0.88Ta _y Nb_{1 ? y} O₃, the superionic transition shows up as a predominant “melting” of the alkali metal sublattice and broadening of the corresponding lines into a Rayleigh line wing, whereas the other sublattices in the structure remain relatively “rigid.” The temperature of the superionic transition can be tuned by varying the degree of static disorder of structural units in the Nb⁵⁺/Ta⁵⁺ sublattice.     

Influence of ball milling on sintering behavior and electrical properties of (Li,Na,K)NbO3 lead-free piezoceramics

Volatilization of alkali elements during sintering process is one of the major factors influencing the processing stability of lead-free (Na,K)NbO₃ (KNN) piezoceramics. With a purpose to reduce sintering temperature by refining particle sizes, an extensive ball-milling step was intentionally introduced to the fabrication process of KNN-based ceramics with a nominal composition of Li_0.058(Na_0.52K_0.48)_0.942NbO₃ by a solid-state powder synthesis and normal sintering method. It was revealed that prolonging the period for milling calcined powders before sintering process significantly reduced the particle sizes and hence sintering temperature. As a result, sintering at a reduced temperature of 1,025 °C resulted in a highly dense material with good piezoelectric and ferroelectric properties with converse piezoelectric coefficient d* ₃₃ and remnant polarization P _r reaching 266 pm/V and 15.7 μC/cm², respectively. This study provided a facile and effective method to enhance the piezoelectric properties in KNN-based ceramics with an optimized composition by reducing the particle sizes.