Effect of poling condition on piezoelectric properties of （K0.5Na0.5）NbO3 ceramics

The lead-free piezoelectric ceramics （K0.5Na0.5）NbO3 （abbreviated as KNN） with the relative density of 97.6% were synthesized by press-less sintering owing to the careful control of processing conditions. The phase structure of KNN ceramics was analyzed. The results show that the pure perovskite phase with orthorhombic symmetry is in all ceramics specimens. The effect of poling conditions on the piezoelectric properties of KNN ceramics was investigated. The results show that the piezoelectric constant d33 and electromechanical coupling factor kp increase with poling field, poling temperature and poling time increasing, then decrease because of electric broken. Take into account of poling conditions and piezoelectric properties of pure KNN ceramics, the optimum poling conditions for pure KNN ceramics are poling field of 4 kV/mm, poling temperature of 140 ℃ and poling time of 20-25 min.     

铋掺杂对（Na0．5K0．5）NbO3无铅压电陶瓷性能的影响

采用传统陶瓷工艺制备了掺铋 （Na0.5K0.5）NbO3（NKN）无铅压电致密陶瓷，研究了Bi2O3对 （Na0.5K0.5）NbO3晶体结构和压电性能的影响。结果表明：当Bi2O3含量小于0．7％（质量分数，下同）时，能得到具有纯钙钛矿结构的NKN基陶瓷，其烧结温度随着Bi2O3掺杂量的增加而升高，试样密度与纯NKN陶瓷相比有显著提高。 （Na0.5K0.5）NbO3压电常数d33，机电耦合系数kp、kt随Bi2O3含量的增加先升高而后降低，并在x=0．5％时达到最大值，而且机械品质因子Qm大大提高。当Bi2O3掺杂量为0．5％时， （Na0.5K0.5）NbO3无铅压电陶的密度达4．46g／cm^3，表现出优异的压电性能，d33=138pC／N，kp=46％，kt=44％，tanδ=2．9％，εr=466和Qm=167。     

Na0.5K0.5NbO3无铅压电陶瓷放电等离子烧结的制备工艺

由于Na,K在高温下容易挥发,因而采用普通陶瓷烧结工艺难以得到致密的碱金属铌酸盐系陶瓷,只能通过热压烧结制备高密度的铌酸钾钠(NaNbO3-KNbO3)系无铅压电陶瓷.本研究采用放电等离子烧结(SparkPlasma Sintering,SPS)技术,通过配料、研磨混料、焙烧、SPS烧结、退火工艺后,制备出白色略带黄色的Na0.5K0.5NbO3压电陶瓷试样.在烧结过程中,没有观察到明显的碱挥发,试样密度随烧结温度的增加而增大,860℃以上温度烧结时,试样的密度达到4.22g/cm3(为理论密度的92%).采用分步极化方法对试样进行极化,即先在高温下用低电压极化,再在低温下用高电压极化,极化后样品的压电常数d33为37pC/N～49pC/N.     

Ag+掺杂Na0.5K0.5NbO3无铅压电陶瓷的无压烧结及性能研究

铅基压电陶瓷在制备、使用及废弃处理过程中都会造成环境污染,随着环保意识的增强,无铅压电陶瓷必将逐步替代铅基压电陶瓷.Na0.5K0.5NbO3是一种很有潜力的无铅压电陶瓷,掺杂各种元素提升Na0.5K0.5NbO3陶瓷的压电性能成为当今研究热点之一.本研究以Ag2O、Na2CO3、K2CO3、Nb2O5为原料,经750 ℃焙烧分别合成了Na0.5K0.5NbO3和AgNbO3粉料,再经配料、混料与成型,在1060 ℃埋粉烧结,制备出Ag+掺杂的Na0.5K0.5NbO3无铅压电陶瓷(xAgNbO3-(1-x)Na0.5K0.5NbO3,ANKN),并在较宽成分范围内(Ag+含量,x=0～50 at%)系统研究了Ag+掺杂对ANKN陶瓷性能的影响.XRD结果表明,ANKN陶瓷的主相为钙钛矿型结构,当x＞16 at%,开始出现K5.75Nb10.85O30杂相,随着Ag掺杂量的增加,杂相的衍射峰增强.电学性能测试结果表明,当x＜20 at%,随Ag掺杂量的增加ANKN陶瓷的压电常数、介电常数等略有升高;当x＞20 at%,ANKN陶瓷的各项性能均开始降低;Ag掺加量为x=16 at%时ANKN陶瓷性能最佳,压电常数d33达到110 pC/N,平面机电耦合系数kp为30%,相对介电常数εr为358,居里温度Tc为300 ℃.     

Ag^＋掺杂Na0．5K0．5NbO3无铅压电陶瓷的无压烧结及性能研究

铅基压电陶瓷在制备、使用及废弃处理过程中都会造成环境污染，随着环保意识的增强，无铅压电陶瓷必将逐步替代铅基压电陶瓷。Na0．5K0．5NbO3是一种很有潜力的无铅压电陶瓷，掺杂各种元素提升Na0．5K0．5NbO3陶瓷的压电性能成为当今研究热点之一。本研究以Ag2O、Na2CO3、K2CO3、Nb2O5为原料，经750℃焙烧分别合成了Na0．5K0.5NbO3和AgNbO3粉料，再经配料、混料与成型，在1060℃埋粉烧结，制备出Ag^＋掺杂的Na0.5K0．5NbO3无铅压电陶瓷（xAgNbO3-（1-x）Na0.5K0．5NbO3，ANKN），并在较宽成分范围内（Ag^＋含量，x=0-50at％）系统研究了Ag^＋掺杂对ANKN陶瓷性能的影响。XRD结果表明，ANKN陶瓷的主相为钙钛矿型结构，当x〉16at％，开始出现K5-75Nb10．85O30杂相，随着Ag掺杂量的增加，杂相的衍射峰增强。电学性能测试结果表明，当x〈20at％，随Ag掺杂量的增加ANKN陶瓷的压电常数、介电常数等略有升高；当x〉20at％，ANKN陶瓷的各项性能均开始降低；Ag掺加量为x=16at％时ANKN陶瓷性能最佳，压电常数d33达到110pC／N，平面机电耦合系数kp为30％，相对介电常数εr为358，居里温度Tc为300℃。     

Mn掺杂(Na1-xKx)0.5Bi0.5TiO3性能研究及其在滤波器上的应用

研究了Mn掺杂对(Na1-xKx)0.5Bi0.5TiO3无铅压电陶瓷性能的影响,并利用该材料研制出中频无铅压电陶瓷滤波器.Mn掺杂改善了(Na0.8K0.2)0.5Bi0.5TiO3体系陶瓷的压电性能,当Mn含量达到0.3%(质量分数)时,d33达到135 pC/N,kp=31%,Qm=183,适用于制作滤波器.采用厚度振动模式,制作出插入损耗为5 dB,中心频率为520 kHz,带宽大于10 kHz,阻带衰耗大于30 dB的中频无铅压电陶瓷滤波器.器件性能接近于同类含铅陶瓷中频滤波器(SFH系列).     

Preparation and dielectric properties of porous silicon nitride ceramics

Porous silicon nitride ceramics with difference volume fractions of porosity from 34.1% to 59.2% were produced by adding different amount of the pore-forming agent into initial silicon nitride powder. The microwave dielectric property of these ceramics at a frequency of 9.36 GHz was studied. The crystalline phases of the samples were determined by X-ray diffraction analysis. The influence of porosity on the dielectric properties was evaluated. The results show that α-Si3N4 crystalline phase exists in all the samples while the main crystalline phase of the samples is β-Si3N4, indicating that the αβ transformation happens during the preparation of samples and the transformation is incomplete. There is a dense matrix containing large pores and cavities with needle-shaped and flaky β-Si3N4 grains distributing. The dielectric constant of the ceramics reduces with the increase of porosity.     

铋基无铅压电陶瓷Bi0.5(Na0.82K0.18)0.5TiO3-BiCrO3的微观组织与电性能

采用传统陶瓷制备方法,制备一种新型无铅压电陶瓷 (1-x)Bi0.5(Na0.82K0.18)0.5TiO3-xBiCrO3 (BNKT-BCx).研究Bi基铁电体BiCrO3对BNKT-BCx陶瓷晶体结构和压电介电性能的影响.结果表明:在所研究的组成范围内,陶瓷材料的主体结构为纯钙钛矿固溶体,微量BiCrO3(x=0～0.02,摩尔分数)不改变陶瓷的晶体结构;当BiCrO3含量x＞0.02时,晶体结构由三方、四方共存转变为伪立方结构,并出现明显的第二相;当x=0.015时,d33=168 pC/N;当x=0.01时,kp=0.32,为该体系压电性能的最大值;随BiCrO3含量的增加,陶瓷的低温介电反常峰向低温移动,高温介电反常峰向高温移动,反铁电相区域增加,弥散指数增加.     

锰掺杂对（Na0.5Bi0.5）TiO3-BaTiO3-（K0.5Bi0.5）TiO3陶瓷介电和压电性能的影响

采用传统陶瓷工艺制备了锰掺杂0.8(Na0.5Bi0.5)TiO3-0.1BaTiO3-0.1(K0.5Bi0.5)TiO3(BNT-B-BKT)无铅压电陶瓷材料,研究了材料的介电、压电和铁电性能.发现锰掺杂大幅降低了0.8(Na0.5Bi0.5)TiO3-0.1BaTiO3-0.1(K0.5Bi0.5)TiO3陶瓷的电导率和矫顽场,最佳掺杂量为0.1%(质量分数),该配方的最佳烧结温度为1150℃.这一温度下烧结所得样品在130℃时的电导率仅为1.36×10-1Ω-1cm-1,约为掺杂前的1/40,矫顽场Ec仅为2.78 kV/mm,剩余极化强度Pr为38μC/cm2,压电系数d33达到143 pC/N.     

(KxNa1-x)NbO3基陶瓷的热稳定性研究

采用传统固溶反应法制备了(KxNa1?x)1-yLiyNb0.80Ta0.20O3 ( x=0.40–0.60 when y=0.030, 0.035, 0.040 ) 系列无铅压电陶瓷,研究了其压电性能的温度稳定性。实验得出在研究的组分范围内,陶瓷的压电常数d33可达到250 pC/N,kp到达50%。在高达约325oC的老化试验中发现,尽管在室温下存在多型相变的影响,但陶瓷的d33和kp值几乎一直保持不变。而且,陶瓷的kp值在-50癈到120癈这个很宽的温度范围内几乎不受温度影响,显示了很好的温度稳定性,笔者从两相共存的温度范围对陶瓷的热稳定性能进行了讨论。     

Piezoelectric and dielectric properties of Lix（K0.46Na0.54） 1-xNb0.86Ta0.1 Sb0.04O3 lead-free ceramics

Lead-free piezoelectric ceramics Lix（K0.46Na0.54）1-xNb0.86Ta0.1Sb0.0403 （with x ranging from 0 to 0.1） were synthesized by conventional solid state sintering method. The effect of cationic substitution of Li for K and Na in the A sites of perovskite lattice on the structure, phase transition behavior and electrical properties were investigated. Morphotropic phase boundaries（MPB） between orthorhombic and tetragonal phase are found in the composition range of 0.06≤x≤0.08. Analogous to Pb（Zr, Ti）O3, the dielectric and piezoelectric properties are enhanced for the composition near the morphotropic phase boundary. The Li0.06（K0.46Na0.54）0.94- Nb0.86Ta0.1Sb0.04O3 ceramics show excellent electrical properties, that is, piezoelectric constant d33=215 pC/N, planar electromechanical coupling factor kp=41%, dielectric constant ε33^T /ε0=1 303, and dielectric loss tan δ=2.45%. The results indicate that Lix（K0.46Na0.54）1 -xNb0.86Ta0.1Sb0.0403 ceramic is a promising lead-free piezoelectric material.     

Piezoelectric and dielectric properties of Cr-doped PSN-PZN-PZT quaternary piezoelectric ceramics

PSN-PZN-PZT x wt.%Cr2O3, x=0.0-0.9, were prepared by conventional mixed oxide techniques at sintering temperatures of 1220℃-1300℃ for 2 h. The effect of sintering temperature on the microstructure and the piezoelectric properties was investigated by XRD, SEM, and other conventional measurement. The result indicated that with temperature increasing, the valence of Cr ion from Cr^5 or Cr^6 changes into Cr^3 , and the piezoelectric properties turn hard. With increasing Cr2O3 content, the amount of rhombohedral phases increases and the morphotropic boundary phase is correspondingly shifts to rhombohedral phase. A uniform microstructure and excellent comprehensive properties were obtained at 1240℃ as the amount of Cr2O3 is 0.5 wt.%.     

Preparation and dielectric properties of compositionally graded （Ba, Sr）TiO3 thin film by sol-gel technique

Compositional graded BaxSr1-xTiO3 （x=0.6, 0.7, 0.8, 0.9, 1.0） （BST） thin films （less than 400 nm） were fabricated on Si and Pt/Ti/SiO2/Si substrates by sol-gel technique. A special heating treatment was employed to form the uniform composition gradients at 700 ℃. The microstructures of the films were studied by means of X-ray diffraction, atomic force microscope and field emission scanning electron microscopy. The results show that the films have uniform and crack-free surface morphology with perovskite structure phase. The small signal dielectric constant （εr） and dielectric loss （tanδ） are found to be 335 and 0.045 at room temperature and 200 kHz. The dielectric properties change significantly with applied dc bias, and the graded thin film show high tunability of 42.3% at an applied field of 250 kV/cm. All the results indicate that the graded BST thin films prepared by sol-gel technique have a promising candidate for microelectronic device.     

Structure and piezoelectric properties of (1–x)K0.5Na0.5NbO3–xLiBiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1–x)(K_0.5Na_0.5)NbO₃–xLiBiO₃ [(1–x)KNN–xLB] (x=0, 0.0005, 0.002, 0.004, 0.006, 0.008, 0.010) were prepared by an traditional solid-state reaction. The microstructure and electrical properties of the ceramics were investigated. The results show that all (1–x)KNN–xLB ceramics possess pure perovskite structure when x=0.01, no trace of any secondary phase is detected, and the phase structure of the ceramics transits abnormally from orthorhombic to cubic. With the increase of the LB content, the size of grain gradually becomes small, the piezoelectric constant d₃₃ and the planar electromechanical coupling coefficient k_p first increases and then decreases. The d₃₃ and k_p of the ceramics reach their maximum values 115 pC/N at x=0.002 and 0.2701 at x=0.001, respectively. The dielectric constant e_r of the ceramics firstly increases evidently and then decreases with the increase of x, the maximum value 871.8 is obtained at x=0.006.     

Ce掺杂0.9Bi4Ti3O12 - 0.1K0.5Na0.5NbO3铋层状陶瓷结构与性能研究

采用传统固相法制备了CeO2掺杂0.9Bi4Ti3O12–0.1K0.5Na0.5NbO3(BTO-KNN) 铋层状陶瓷材料。系统研究了CeO2掺杂对BTO-KNN基陶瓷物相结构、微观结构以及电性能的影响. 结果表明：所有陶瓷样品均为单一的铋层状结构;BTO-KNN基陶瓷的压电性能随着CeO2的掺杂而显著提高,损耗明显降低。当CeO2掺量为0.75 wt% 时,样品具有最佳的电性能: d33=28 pC/N,介电损耗tan δ=0.29%,机械品质因数Qm = 2897,剩余极化强度Pr = 11.83 μC/cm2,且居里温度 Tc 高达615 ℃;研究结果表明CeO2掺杂0.9Bi4Ti3O12–0.1K0.5Na0.5NbO3铋层状陶瓷是种潜在的高温陶瓷材料。     

Preparation and properties of Ba3ZnzCo2-zFe24O41／SiO2 microcrystalline glass ceramics

Ba3ZnzCo2-zFe24O41/SiO2(Z varies from 0.0 to 1.2 in step of 0.4) microcrystalline glass ceramics were prepared by citrate sol-gel process at 1200℃ in the system of BaO-Fe2O3-CoO-ZnO-SiO2. The samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The complex dielectric constant and complex permeability of Ba3ZnzCo2-zFe24O41/SiO2 microcrystalline glass ceramics were measured in the range of 0.1-6.0 GHz by transmission/reflection coaxial line method. The natural resonance phenomenon was observed in μ”spectra for all the Ba3ZnzCo2-zFe24O41/SiO2 microcrystalline glass ceramics, which was closely affected by the substitution of Zn^2 ion.     

掺Sr改性Bi0．5（Na0．8K0．2）0．5TiO3无铅压电陶瓷的微观结构和性能研究

采用传统的陶瓷工艺制备了Sr掺杂Bi0.5（Na0.8K0．2）0．5TiO3无铅压电陶瓷（化学式为[Bi0.5（Na0.8K0．2）0．5]1-xSrxTiO3，x=0～0．1），研究了Sr掺杂对陶瓷样品的微观结构、压电以及介电性能的影响。X射线衍射结果表明：当掺杂量较小时（x=0，0．02），样品为四方相；随着掺杂量的增加（x=0．04～0．1），样品逐渐转变为三方相。压电与介电性能测试结果表明：样品的压电常数西3和机电耦合系数kp开始时都随着X的增加而逐渐增大，并分别在x=0．06和x=0．04时达到最大值，其后随着X的增加都逐渐减小：样品的介电常数ε^T33／ε0则随X的增加而几乎线性增加。在x=0．06时，样品的d33=178pC／N，kp=31％，ε^T33／ε0=850。     

（Bi0．5Na0．5）TiO3-（Bi0．5K0．5）TiO3陶瓷在准同型相界附近的铁电和压电性能

通过传统的固相烧结法合成（1-x）（Bi0.5Na0.5）TiO3-x（Bi0.5K0.5）TiO3陶瓷（x选取范围0．135-0．24）。先在850℃合成原料粉体，然后在1100～1200℃下烧结得到陶瓷样品。分析检测该体系陶瓷的结构以及铁电、压电性能。x射线衍射分析结果表明，该二元系准同型相界（MPB）区域位于x=0．165～0．225附近。对这一体系铁电和压电性能进行测试，并对其在准同型相界附近的电学性能发生变化的机理作了讨论。（Bi0．5Na0．5）TiO3-（Bi0.5K0.5）TiO3是一种很有应用前景的无铅压电陶瓷材料，值得进一步的研究和探索。同时，本实验还对密封烧结工艺对无铅压电陶瓷性能的影响作了初步的研究。     

Effects of molybdenum on the microstructure and mechanical properties of Ti（C,N）-based cermets with low Ni

The effects of Mo on the microstructure and mechanical properties of Ti（C,N）-based cermets with low Ni have been studied systematically. Different contents of Mo （4-12 wt.%） were added into Tl（C,N）-based cermets. Specimens were fabricated by conventional powder metallurgy and vacuum sintered at temperatures of 1440, 1450, and 1460℃ individually. The microstructure and fracture morphology were investigated by scanning electron microscope, and the mechanical properties such as transverse strength and hardness were measured. The results show that the microstructure is uniform and the thickness of rim phase is moderate when the content of Mo is 8 wt.%; the mechanical properties of the specimens sintered at 1450℃ are better than those sintered at 1440 and 1460℃. The integrated properties of transverse strength and hardness are the best when the content of Mo is 8 wt.% and the sintering temperature is 1450℃.