Reactive templated grain growth and anisotropic electrical properties of (Na0.5K0.5)NbO3 ceramics without sintering aids

(Na_0.5K_0.5)NbO₃ (KNN) ceramics with {100} orientation without sintering aids were fabricated by a conventional process and reactive templated grain growth using tabular NaNbO₃ template particles. The KNN specimen sintered at 1,170?°C for 15?h were found to have a relative density of 95.6%. The experimental results show that the textured ceramics have a pseudo-cubic {100} orientation degree of 96.2% and a microstructure with brick-like grains aligning in the direction parallel to the casting plane. The dielectric constant is much higher than the value for non-textured ceramics. Transition temperatures (T _o–t, T _c) are reduced and dielectric peaks are greater breadth. Remanent polarization P _r decreased from 19.40 (the random KNN) to 13.77 (textured KNN) μC/cm². The textured ceramics show anisotropic electrical properties between different directions of textured KNN ceramics, and show a very high electromechanical coupling factor k _p?=?0.58 and a high piezoelectric constant d ₃₃?=?225?pC/N, compared to the random counterparts (k _p?=?0.31, d ₃₃?=?115?pC/N).     

Photoluminescence and electrical properties of Er-doped (K0.5Na0.5)NbO3-based transparent ceramics

Er-doped 0.98(K_0.5Na_0.5)NbO₃-0.02Ba(Bi_0.5Nb_0.5)O₃ transparent fluorescent ceramics were prepared using traditional solid-phase method. The (K_0.5Na_0.5)NbO₃ (KNN) ceramics were modified by introducing the second group elements Ba(Bi_0.5Nb_0.5)O₃ and rare earth ions Er³⁺. The effects of Er³⁺ on the structure, optical and electrical properties of transparent ceramics (K_0.5Na_0.5)NbO₃-Ba(Bi_0.5Nb_0.5)O₃ were investigated. The ceramics form a single perovskite structure and have a pseudo-cubic phase structure. Nanoscale grain size was obtained for ceramics, and the smallest average grain size is 80 nm. The ceramics have high transmittance. The ceramic 0.1 mol% Er-doped 0.98(K_0.5Na_0.5)NbO₃-0.02 Ba(Bi_0.5Nb_0.5)O₃ achieved the highest transmittance for this system with 62% and 52% at near-infrared light (1000 nm) and visible light (700 nm), respectively. The ceramics have up-conversion luminescence properties and also maintain good electrical properties. Under 980 nm excitation, the samples showed two green emission bands (518–536 nm, 536–557 nm) and one red emission band (646–677 nm). In addition, the ceramics have relaxation ferroelectricity, and a high dielectric constant. These functional ceramics with multiple properties will have greater research significance and application value.

     

Structural,transmittance, ferroelectric,energy storage,and electrical properties of K0.5Na0.5NbO3 ceramics regulated by Sr(Yb0.5Ta0.5)O3

Journal of Materials Science: Materials in Electronics - High transparent lead-free (1?x)K0.5Na0.5NbO3-xSr(Yb0.5Ta0.5)O3 (KNN-xSYbT, x = 0.005, 0.01, 0.02, 0.03, 0.04, 0.05) ferroelectric...     

BiFeO3-doped (Na0.5K0.5)NbO3 lead-free piezoelectric ceramics

Abstract

Lead-free piezoelectric ceramics (1?x)(Na_0.5K_0.5)NbO₃-xBiFeO₃ (x=0～0.07) were synthesized by the solid-state reaction. Differential scanning calorimetry (DSC) measurements revealed that an increase in the amount of BiFeO₃ dopant resulted in a decrease in the orthorhombic-tetragonal and tetragonal-cubic phase transition temperature of the material. One percent BiFeO₃ additive suppressed grain growth, which not only benefits the sintering of ceramics but also enhances the piezoelectric and ferroelectric properties, where d₃₃=145pC/N, k_p=0.31, Q_m=80, P_r=11.3 μC cm^?2 and E_c=16.5 kV cm^?1. As x_BF>0.01, both piezoelectric and ferroelectric properties decreased rapidly with an increasing amount of dopant.     

Lead-free (Li, Na, K)(Nb, Sb)O3 piezoelectric ceramics: effect of Bi(Ni0.5Ti0.5)O3 modification and sintering temperature on microstructure and electrical properties

Lead-free (1 ? x)(K_0.475Na_0.475Li_0.05)(Nb_0.95Sb_0.05)O₃–xBi(Ni_0.5Ti_0.5)O₃ [(1 ? x)KNNL–xBNiT] piezoelectric ceramics were prepared by conventional solid-state sintering. The effect of BNiT addition and sintering temperature on phase structure, microstructure, and dielectric and piezoelectric properties of (1 ? x)KNNL–xBNiT ceramics was investigated. The results reveal that the addition of small amounts of BNiT causes significant changes in microstructures, crystalline structures, and dielectric and piezoelectric properties. The T _c values and dielectric constant at T _c of (1 ? x)KNNL–xBNiT ceramics are increased obviously with 0.2 % BNiT addition and decreased with further increasing BNiT content. Enhanced piezoelectric properties are obtained for the sample with x = 0.4 % and synthesized at optimal temperature of 1100 °C, in which d ₃₃ and k _p are 253 pC/N and 0.52, respectively. These results show that (1 ? x)KNNL–xBNiT ceramics are promising lead-free piezoelectric materials.     

BiFeO3-doped (Na0.5K0.5)NbO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1−x)(Na_0.5K_0.5)NbO₃-xBiFeO₃ (x=0∼0.07) were synthesized by the solid-state reaction. Differential scanning calorimetry (DSC) measurements revealed that an increase in the amount of BiFeO₃ dopant resulted in a decrease in the orthorhombic-tetragonal and tetragonal-cubic phase transition temperature of the material. One percent BiFeO₃ additive suppressed grain growth, which not only benefits the sintering of ceramics but also enhances the piezoelectric and ferroelectric properties, where d₃₃=145pC/N, k_p=0.31, Q_m=80, P_r=11.3 μC cm⁻² and E_c=16.5 kV cm⁻¹. As x_BF>0.01, both piezoelectric and ferroelectric properties decreased rapidly with an increasing amount of dopant.     

(Na0.5K0.5)NbO3–LiTaO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics were prepared in the system (1−x)(Na_0.5K_0.5)NbO₃–xLiTaO₃ following the conventional mixed oxide route. The effect of cationic substitution of lithium for sodium and potassium in the A sites and tantalum for niobite in the B sites in (Na_0.5K_0.5)NbO₃ (NKN) perovskite lattice on symmetry and physical properties were investigated. The materials with perovskite structure are in orthorhombic phase when x<5 mol.% and transform to tetragonal phase when x>6 mol.%; when x≥8 mol.%, a K₃Li₂Nb₅O₁₅ phase with tetragonal tungsten bronze structure begins to appear and becomes dominant with increasing content of LiTaO₃. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal phases appears at x=5–6 mol.%. Analogous to Pb(Zr,Ti)O₃, the piezoelectric and electromechanical properties are enhanced for compositions near the morphotropic phase boundary. Piezoelectric constant d₃₃ values reach ∼200 pC/N. Electromechanical coefficients of planar mode reach ∼36%, respectively. Our results show that (Na_0.5K_0.5)NbO₃ with small amount of LiTaO₃ (x=7 mol.%) is a good lead-free piezoelectric ceramic.     

Effect of V2O5 additive to 0.4SrTiO3–0.6La(Mg0.5Ti0.5)O3 ceramics on sintering behavior and microwave dielectric properties

The effect of V₂O₅ addition on the microwave dielectric properties and the microstructures of 0.4SrTiO₃–0.6La(Mg_0.5Ti_0.5)O₃ ceramics sintered for 5 h at different sintering temperature were investigated systematically. It was found that the sintering temperature was effectively lowered about 200 °C by increasing V₂O₅ addition content. The grain sizes, bulk density as well as microwave dielectric properties were greatly dependent on sintering temperature and V₂O₅ content. The 4ST–6LMT ceramics with 0.25% V₂O₅ sintered at 1400 °C for 5 h in air exhibited optimum microwave dielectric properties of ɛ_r = 50.7, Q × f = 15049.6 GHz, T_f = −1.7 ppm/°C.     

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.     

Effects of Ba(Mg1/3Ta2/3)O3 doping on phase structure,optical and electrical properties of (K0.5Na0.5)NbO3 transparent ferroelectric ceramics

Journal of Materials Science: Materials in Electronics - This paper takes KNN ceramics as the research object, and introduces the second component of ABO3 type perovskite structure into it. A...     

LiTaO3掺杂对K0.5Na0.5NbO3基无铅压电陶瓷性能的影响

采用传统陶瓷工艺制备了LiTaO3掺杂的K0.5Na0.5NbO3基无铅压电陶瓷(记为KNN xLT,x=0～8%(摩尔分数)),并研究了陶瓷的晶相、显微结构和压电、铁电等性能.研究结果表明,KNN xLT陶瓷的正交相-四方相准同型相界(MPB)位于4%＜x＜6%处.随着LiTaO3含量的增加,陶瓷的正交→四方结构相变温度(TO-T)向低温方向移动,而四方→立方结构相变温度(Tc)向高温方向移动.陶瓷的压电常数d33和机电耦合系数kp随LiTaO3含量的增加均先增大后减小,而剩余极化强度Pr则随之逐渐减小,矫顽场Ec逐渐增大.当x=6%时,陶瓷具有较好的压电和铁电性能:d33=190pC/N,kp=40.0%,Pr=22.0μC/cm2,Ec=1.78kV/mm,Tc=440℃.该体系陶瓷具有较高的压电常数和比较大的平面机电耦合系数,是一种应用前景良好的压电铁电材料.     

Fabrication of lead-free piezoelectric (Na(0.5)K(0.5))NbO(3) ceramics by a modified solid-state reaction method

Sodium potassium niobate, (Na(0.5)K(0.5))NbO(3), fine powder has been successfully synthesized at the low temperature of 550 degrees C through a modified solid-state reaction method, in which urea [CO(NH(2))(2)] plays an important role. High-density (Na(0.5)K(0.5))NbO(3) ceramics could be obtained by conventional sintering of the synthesized (Na(0.5)K(0.5))NbO(3) fine powder with the addition of 0.03 mol% Co(3)O(4) as a sintering additive. The crystal structure, microstructure, and dielectric and piezoelectric properties were characterized. The (Na(0.5)K(0.5))NbO(3) ceramic showed a comparatively saturated P-E hysteresis loop. The (Na(0.5)K(0.5))NbO(3) ceramic also displayed piezoelectricity with a piezoelectric constant d(33) of 126 pC/N and a planar electromechanical coupling factor k(p) of 33%.     

Effects of Nb5+ doping on sintering and electrical properties of lead-free (Bi0.5Na0.5)TiO3 ceramics

The Nb⁵⁺ doped (Bi_0.5Na_0.5)TiO₃ (BNT) ceramics were manufactured by a conventional solid state reaction method. The influence of Nb⁵⁺ doping on the sintering, microstructure and various electrical properties of BNT ceramics was investigated. The results of X-ray diffraction show that the solubility limit of Nb⁵⁺ in the BNT lattice is less than 3%. Additionally, Nb⁵⁺ doping produces significant effects on the densification and grain growth of BNT ceramics. Various electrical properties of BNT ceramics are obviously changed with doping a small amount of Nb⁵⁺. The ferroelectric and piezoelectric properties display enhanced values at a low doping level. The formation of A-site vacancies is considered as the reason for the changed ferroelectric and electromechanical behavior.     

Preparation and piezoelectric properties of CuO-doped (Na0.5K0.5)NbO3 ceramics by the citrate precursor method

A low-cost citrate so-gel route was investigated to synthesize nano-sized crystalline powders (<100 nm) of 1 mol% CuO modified (Na_0.5K_0.5)NbO₃ compositions. It was found that amorphous gels can be transformed into crystallite powders with single-phase perovskite structure when calcined at 500?C600 °C for 3 h. The transmission electron microscopy observation showed that the particles are column-like and well dispersed, depending on the calcination condition. The as-pressed samples exhibit improved densification behavior and finer grain morphology after sintering. Electrical properties of the samples sintered at 1,060 °C are as follows: dielectric constant ?? _r  = 605, piezoelectric constant d ₃₃ ~ 117 pC/N, planar electromechanical coupling factor k _p  ~ 0.38 and mechanical quality factor Q _m  ~ 725.     

Influence of zirconium addition on final properties of K0.5Na0.5NbO3-based ceramics

Microstructure, electrical and dielectric properties of K_1/2Na_1/2NbO₃ (KNN) modified with ZrO₂ were investigated. Powders were obtained by a conventional solid-state method. Samples doped with 0–2 mol% of ZrO₂ were sintered at 1,125 °C for 2 h. Through XRD spectra, the perovskite structure was observed, in addition to small peaks corresponding to secondary phases. It was also determined that zirconium drastically changed the microstructure and grain size of KNN ceramics. The addition of upto 1.0 mol% of Zr⁴⁺ produced a softening effect in the ferroelectric properties of the material, and increased its density. Conversely, samples prepared with contents higher than 1.0 mol% reduced piezoelectric and dielectric properties.     

铌酸钠钾基压电陶瓷的结构与性能研究

采用传统的固相反应合成法制备了结构较为致密的0.9(K0.5Na0.5)NbO3-0.1LiSbO3(KNN-LS)无铅压电陶瓷,研究了其相结构、压电、介电、损耗以及铁电性质.常温下的压电陶瓷具备四方钙钛矿结构,具有较高的压电系数d33=131pC/N和低的介电损耗tanδ=0.09(10kHz)等优点.另外,常温下的KNN-LS陶瓷存在着较为饱满的电滞回线,其剩余极化率Pr为16.1μC/cm2,矫顽场为EC=14.8kV/cm.性能较KNN压电陶瓷有了较大的提高.