Comparative study of 2mol%Li-and Mn-substituted lead-free potassium sodium niobate ceramics

The effect of Li and Mn substitution on the dielectric, ferroelectric and piezoelectric properties of lead free K0.5Na0.5NbO3 （KNN） was investigated. Samples were prepared using a conventional solid state reaction method. The sintefing temperature for all the samples was 1050℃. The optimum doping concentration for the enhancement of different properties without the introduction of any other co-dopants such as Ti, Sb, and La was investigated. X-ray diffraction analysis confirmed that all the samples crystallize in a single phase perovskite structure. The dielectric properties were investigated as a function of temperature and applied electric field frequency. Compared with Li-substituted KNN （KLNN）, Mn-substituted KNN （KMNN） exhibited a higher dielectric constant εmax （i.e., 4840） at its critical transition temperature Tc （i.e., 421℃） along with a lower value of tangent loss at 10 kHz and greater values of saturation polarisation Ps （i.e., 20.14 μC/cm^2） and remnant polarisation Pr （i.e., 15.48 μC/cm^2）. The piezoelectric constant （d33） of KMNN was 178 pC/N, which is comparable to that of lead-based hard ceramics. The results presented herein suggest that B-site or Mn substitution at the optimum concentration results in good enhancement of different properties required for materials used in memory devices and other applications.     

Bi1/2Na1/2TiO3-Bi1/2Na1/2(Nb2/3Zn1/3)O3-BaTiO3无铅陶瓷压电介电性能

采用传统陶瓷制备方法,制备出新型无铅压电陶瓷,并对该体系无铅陶瓷的相结构、介电和压电性能进行了研究.结果表明:所研究的组成均能够形成纯钙钛矿(ABO3)型固溶体;随着BaTiO3含量的增加,压电系数d33先增大后减小.同时陶瓷材料的介电常数-温度曲线显示该体系材料具有明显的弛豫铁电体特征.     

Hydrothermal synthesis and dielectric properties of lanthanum titanate ceramics

Lanthanum titanate (La2/3 TiO3) powders were synthesized by hydrothermal method based on the reaction of TiO2, La(NOa)a and KOH at 160℃ for 24 h followed by the treatment of acidification. The microstructure,morphology and dielectric properties were investigated by using X-ray diffraction, scanning electron microscope,transmission electron microscope and impedance method. The results show that the La2/a TiOa particles consist of nearly homogenous and lamellar grains. The particles can be sintered into porous ceramics above 1 150℃. The dielectric properties of La2/3 TiO3 show that both the dielectric constant and the dielectric loss tangent decrease with the increase of frequency.     

Dielectric tunable properties of BaTi_4O_9-doped Ba_(0.6)Sr_(0.4)TiO_3 microwave composite ceramics

BaTi4O9-doped Ba0.6Sr0.4TiO3 (BST) composite ceramics were prepared by the conventional solid-state reaction and their structure, dielectric nonlinear characteristics and microwave dielectric properties were investigated. The secondary phase of the orthorhombic structure Ba4Ti13O30 is formed among BST composite ceramics with the increase of BaTi4O9. At the same time, a duplex or bimodal grains size distribution shows fine grains in a coarse grain matrix. The degree of frequency dispersion of dielectric permittivity below Tm is increased initially and then decreased with respect to BaTi4O9. As the BaTi4O9 content increases, the tunability of composite ceramics decreases, while the Q value increases. Inter-estingly, 70 wt% BaTi4O9-doped BST has a tunability ~4.0% (under 30 kV/cm biasing) versus a permit- tivity ~68 and quality factor ~134.1 (at ~3.2 GHz).     

La2O3、Cr2O3共掺杂的CCTO陶瓷介电性能研究

采用氧化物混合工艺制备了La2O3和Cr2O3共掺杂的CaCu3Ti4O12(CCTO)陶瓷材料。通过XRD、介电温度特性等测试手段,研究了掺杂不同浓度的La2O3和Cr2O3对CCTO体系陶瓷介电性能的影响,并对掺杂机理进行了分析.研究结果表明:分别掺杂La2O3和Cr2O3的CCTO陶瓷的介电损耗为～0.2,比纯的CCTO陶瓷样品低,而介电常数仍保持在～104;掺杂0.03at%La2O3和0.08at%Cr2O3的CCTO陶瓷材料的介电常数为4.4×104,介电损耗可降至0.15.因此,通过共掺杂的方法可以在有效降低CCTO陶瓷介质损耗的同时,仍维持高的介电常数.     

CuO-TiO2复合纳米粉制备及其原位掺杂Al2O3微波介质陶瓷

研究了CuO-TiO₂复合纳米粉制备方法以及原位掺杂Al₂O₃微波介质陶瓷.采用溶胶-凝胶法低温合成出平均粒径为50 nm的CuO-TiO₂复合纳米粉体.CuO-TiO₂凝胶在Al₂O₃粉体表面形成均质的胶状体,胶状体在750 ℃热处理后,原位形成CuO-TiO₂纳米粒子,温度升高到1 030 ℃左右,生成CuO-TiO₂低熔点化合物,促使Al₂O₃烧结温度降至1 320 ℃,剩余的TiO₂ 均匀分布在Al₂O₃ 陶瓷中,起调节频率温度系数作用.掺杂摩尔分数为0.5%的CuO和10%的TiO₂的Al₂O₃ 陶瓷在1 320 ℃烧结3 h,具有良好的介电性能：介电常数为10.92, 品质因子为30 540 GHz, 频率温度系数为-5.6×10-6/℃.     

Microstructure and strength modification of relaxor ferroelectric ceramics through microwave sintering for multilayer capacitors

Relaxor ferroelectric ceramics with the composition of xPb( Mg_(1/3) Nb_(2/3)O_3-yPb (Zn_(1/3)Nb_(2/3)O_3-zPbTiO_3 was fast sintered in a 2.45 GHz microwave system. Microwave-sintered samples illustrate more rapid densification and much smaller grain size microstructure than eonventional sintered samples. Also the microwave processing significantly increases the dielectric strength and flexural strength of the relaxor so that its strength becomes comparable with modified BaTiO_3, and could obtain comparable dielectric properties in comparison with conventional sintering process. Microwave processing has many advantages for sintering of relaxor ferroelectrie ceramics used as multilayer capacitors.     

Dielectric and Piezoelectric Properties of 0-3 PZT/PVDF Composite Doped with Polyaniline

Lead zirconate titanate （ PZT ） / polyvinylidene fluoride （PVDF） 0-3 piezoelectric composites doped with polyaniline （PANI） were obtained by hot-press method. The polarization properties of the composites were characterized by XRD and P- E hysteresis loops at room temperature. And the dielectric and piezoelectric properties were also measured. The results show that the poling of PZT could be effectively carried oat and the dielectric constant e, and dissipation tanδ increase monatonously by increasing the volume fraction of PANI in the composite. The piezoelectric constant d33, and the planar electromechanical coupling factor kp increase while the mechanical quality factor Qm decreases with the increase in the content of PANI. The d33, kp and Qm show the extremum values at 8 vol%-10 vol% PANI.     

烧结温度对BaTiO3多孔陶瓷性能的影响

采用水基冷冻浇注法制备了具有层状结构的BaTiO3多孔陶瓷,研究了烧结温度对多孔陶瓷微观形貌、收缩率、孔隙率及介电性能的影响,并探讨了高岭土悬浮剂在烧结过程中所起的作用.研究结果表明:高岭土含量4wt%的样品收缩率从1 200℃时的27%升高到1 220℃时的56%,同时孔隙率从78%下降到56%,高岭土含量8wt%的样品收缩率从1 200℃时的30%升高到1 220℃时的61%,同时孔隙率从72%下降到39%;高岭土在烧结过程中起到烧结助剂的作用;烧结温度升高会使孔径变小并导致孔隙排列由有序结构向无序结构转变.高岭土含量为8wt%,烧结温度1 200℃时,可以得到分布均匀的层状结构多孔陶瓷;高岭土含量为4wt%,烧结温度1 220℃时可得到介电常数130的多孔陶瓷.     

Structure and Electrical Properties of （Na0.5Bi0.5）0.94Ba0.06TiO3 Ceramicwith0.5wt% of MnO

The structure and electrical properties of （Na0.5Bi0.5）0.94Ba0.06TiO3 ceramic doped with 0.5 wt% of MnO were investigated in comparison with those of （Na0.5Bi0.5）0.94Ba0.06TiO3 ceramic. It was ascertained that the MnO addition did not cause remarkable change in crystal structure and microstructure. The MnO addition mainly displayed a hard effect on the electrical properties, an increase of coercive field （E） and mechanical quality factor （Qm） together with a decrease of dielectric constant （εr） and piezoelectric constant （d33）. An enhancement of electromechanical coupling factor （kp） with the MnO addition was obtained too. An essential relation between the piezoelectric properties and ferroelectric nature of the ceramics was detected. It was found that the piezoelectric properties of the ceramics highly depended on the corporative contribution of remanent polarization （Pt） and coercive field.     

Sb掺杂对0.95MgTiO3-0.05CaTiO3陶瓷介电性能的影响

采用固相反应法制备了( Mg0.95-X Ca0.05 SbX) TiO3微波介质陶瓷.研究了Sb掺杂对0.95MgTiO3-0.05 CaTiO3 (95MCT)陶瓷性能的影响.结果表明:Sb掺杂95MCT陶瓷的主晶相为MgTiO3和CaTiO3两相,有中间相MgTi2O5的产生;Sb掺杂能有效的降低95 MCT陶瓷...     

Sr/Zr掺杂以及抛光对BaTiO_3陶瓷结构和介电性能的影响

采用冷压陶瓷技术制备了(Ba0.75Sr0.25)TiO3、Ba(Ti0.8Zr0.2)O3、(Ba0.75Sr0.25)(Ti0.8Zr0.2)O3陶瓷.XRD结果表明,Sr和Zr在BaTiO3的Ba位、Ti位、及Ba/Ti双位并入均具有高固溶性,且为没有超结构特征的单相钙钛矿结构.Sr/Zr的双位并入加快介电峰向低温的移动.Sr掺杂对Ba(Ti0.8Zr0.2)O3介电峰移动率的贡献为-1.5℃/mol%Sr.抛光技术对介电温谱的影响研究表明,尽管水抛光导致(Ba0.75Sr0.25)(Ti0.8Zr0.2)O3陶瓷颜色变暗,但晶体结构不变、介电峰值降低.     

Struchre and Electrical Properties of (Na0.5Bi0.5)0.94Ba0.06TiO3 Ceramic with 0.5 wt% of MnO

The structure and electrical properties of(Na0.5Bi0.5)0.94Ba0.06TiO3 ceramic doped with 0.5 wt% of MnO were investigated in comparison with those of(Na0.5Bi0.5)0.94Ba0.06TiO3 ceramic.It was ascertained that the MnO addition did not cause remarkable change in crystal structure and microstructure.The MnO addition mainly displayed a hard effect on the electrical properties,an increase of coercive field(Ec)and mechanical quality factor(Qm)together with a decrease of dielectric constant(?r)and piezoelectric constant(d33).An enhancement of electromechanical coupling factor(kp)with the MnO addition was obtained too.An essential relation between the piezoelectric properties and ferroelectric nature of the ceramics was detected.It was found that the piezoelectric properties of the ceramics highly depended on the corporative contribution of remanent polarization(Pr)and coercive field.     

微波介质陶瓷的研究现状与发展趋势

微波介质陶瓷是现代通信技术中关键基础材料，它的应用越来越受到人们的重视。介绍了低介电常数、中介电常数、高介电常数三类微波介质陶瓷的研究现状，并根据材料设计的思想对高性能微波介质陶瓷的发展趋势进行了探讨。     

Dielectric tunable properties of BaTi<Subscript>4</Subscript>O<Subscript>9</Subscript>-doped Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> microwave composite ceramics

BaTi₄O₉-doped Ba_0.6Sr_0.4TiO₃ (BST) composite ceramics were prepared by the conventional solid-state reaction and their structure, dielectric nonlinear characteristics and microwave dielectric properties were investigated. The secondary phase of the orthorhombic structure Ba₄Ti₁₃O₃₀ is formed among BST composite ceramics with the increase of BaTi₄O₉. At the same time, a duplex or bimodal grains size distribution shows fine grains in a coarse grain matrix. The degree of frequency dispersion of dielectric permittivity below T _m is increased initially and then decreased with respect to BaTi₄O₉. As the BaTi₄O₉ content increases, the tunability of composite ceramics decreases, while the Q value increases. Interestingly, 70 wt% BaTi₄O₉-doped BST has a tunability ∼4.0% (under 30 kV/cm biasing) versus a permittivity ∼68 and quality factor ∼134.1 (at ∼3.2 GHz). Supported by the Ministry of Science and Technology of China through 973-project (Grant No. 2009CB623302), the Cultivation Fund of the Key Scientific and Technical Innovation Project, Ministry of Education of China (Grant No.707024), Shanghai Committee of Science and Technology (Grant No. 07DZ22302), and Shanghai Foundation Project under 06JC14070     

Effect of doped Mn on piezoelectric properties of (Na_(0.5)Bi_(0.5))_ (0.92)Ba_(0.08)TiO_3 lead-free ceramics

1INTRODUCTION Therehasbeengreatinterestinthestudiesof thelead freematerialswithdielectric,piezoelectricandferroelectricpropertiesinthefieldoffunction almaterialsfortheiramiabilitytoenvironment. (Na1/2)TiO3(NBT)ceramicshavebeenwidelystudiedbecauseoftheirrelativelylargeremnant polarization(Pr)of38μC/cm2andcoercivefieldof 73kV/cm[1].However,NBTcannotreplacelead zirconatetitanate(PZT)basedceramicsbecausethepiezoelectricpropertiesofNBTarestillnot comparabletothoseofPZT[24].Recently,m…     

微波介质陶瓷和复合钙钛矿结构的研究

微波介质陶瓷是现代移动通信技术中被广泛应用的关键新材料。分析了微波介质陶瓷的分类和应用，讨论了钙钛矿结构的特点和微波介质陶瓷的性能要求，提出了复合钙钛矿结构将会在微波介质陶瓷的研究开发领域得到广泛应用。     

Low-temperature sintering and microwave dielectric properties of Li2MgTi3O8 ceramics doped with BaCu（B2O5）

The influences of BaCu(B₂O₅) (BCB) addition on sintering, microstructure and microwave dielectric properties of Li₂MgTi₃O₈ ceramics were investigated using X-ray diffractometry, scanning electron microscopy and microwave dielectric measurements. The experimental results show that a small amount of BaCu(B₂O₅) addition can effectively reduce the sintering temperature to 900 °C, and induce only a limited degradation of the microwave dielectric properties. Typically, the best microwave dielectric properties of ɛ _r=24.5, Q×f =24 622 GHz, τ _f=4.2×10⁻⁶ °C⁻¹ are obtained for 1.0% BCB-doped Li₂MgTi₃O₈ ceramics sintered at 900 °C for 3 h. The BCB-doped Li₂MgTi₃O₈ ceramics can be compatible with Ag electrode, which may be a strong candidate for low temperature co-fired ceramics applications.