Sintering and dielectric properties of fine-grained BaTiO_3 ceramics

A new sintering method, spark plasma sintering (SPS), is described for the sintering of fine-grained BaTiO_3 ceramics. Dense ceramics with fine grain size of near 170 nm are obtained using SPS at low temperature of 900℃ without holding time. The dielectric measurements of various grain size specimens show that the dielectric constants decrease with the reduce of grain size, and diffuse phase transition showed in the dielectric-temperature spectra. The variation in dielectric properties with grain size is explained.     

The Dielectric Properties and Preparation Method of BaTiO3/PVDF 0-3 Composites

A series of 0-3 composties of the polyvinylidene fluoride (PVDF) and BaTiO3 was prepared,BaTiO3 was modified with titanate coupling agent .The dielectric properties and the interfacial interaction of composites by different preparation methods were examined and compared,The result shows that the relaive dielectric constant ε of the composite prepared in solution has a maximum value at about 70% weight fraction of BaTiO3 and the dielectric loss tanδ increases rapidly when the fraction exceeds 70%, For the composite preared in melt, the relative dielectric constant ε almost raches a maximum value at about 60% weght fraction of BaTiO3 and the dielectric loss is comparatively lower,The deielectric proerties of composites ore improved by using a coupling aent.     

镨对锰掺杂钛酸钡陶瓷结构和介电性能的影响

采用冷压陶瓷技术制备了锰掺杂及镨锰共掺杂钛酸钡陶瓷.1.0%锰在钛酸钡中的掺杂导致形成四方和六方钙钛矿混合结构;镨的进一步掺杂导致六方相消失,形成四方钙钛矿单相结构.同时研究了镨对锰掺杂钛酸钡陶瓷介电性能的影响.     

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.     

Dielectric Behavior of BaTiO3／ PVDF Nanocomposites In-situ Synthesized by the Sol-Gel Method

BaTiO3/ PVDF nanocomposites were prepared via in-situ growth of nanosized BaTiO3 particles in PVDF matrix by using the sol-gel method. The present elements of BaTiO3/ PVDF nanocomposites were analyzed by an electron probe X-ray microanalyser. Nanosized BaTiO3 grown in the composite films was characterized by an X-ray diffractometer and a transmission electron microscope, and the dielectric properties of the composite films were measured. The distribution of BaTiO3 nanoparticles in-situ grown in the PVDF matrix was examined using a scanning electron microscope.     

Phase structure and electrical properties of La<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped BiInO<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> ceramics with high curie temperature

The phase structure and electrical properties of pure and La2O3-doped Bi-InO3-PbTiO3 （BI-PT） ceramics were studied respectively. In （1 -x）BI-xPT （x=0.72-0.80） ceramics, the stability of tetragonal phase increased with increasing x, and pure perovskite structure was obtained for x=-0.80 ceramics. The phase transition temperature range was between 575 ℃ and 600 ℃ for x=0.72-0.80 ceramics, higher than that of PT （-490 ℃）. The c/a ratio almost linearly decreased with increasing La2O3 content in x-0.80 ceramics. It is believed that Pb^2＋ vacancies were formed by La^3＋ substituting Pb^2＋ in La2O3-doped BI-PT ceramics. Tc shifted to lower temperature by 30 ℃/mol% La2O3. The maximum dielectric constant 8557 around 559 ℃ was exhibited in 0.5mol%-doped BI-0.80PT ceramics. La2O3-doped ceramics could be poled resulting from decreasing of c/a ratio and improving of dielectric loss and resistivity. The maximum piezoelectric coefficient d33 was 12 pC/N for 2mol%-doped BI-0.80PT ceramics.     

Preparation of nanocrystalline BaTiO<Subscript>3</Subscript> ceramics

The high-dense nanocrystalline BaTiO₃ (BT) ceramics with grain size smaller than 100 nm have been successfully prepared by the two step sintering and the spark plasma sintering (SPS) process. The successive transitions in nanograin BT ceramics from rhombohedral to orthorhombic, tetragonal and cubic transitions, similar to those in coarse BT ceramics, were revealed by in-situ temperature dependent Raman spectrum. The multiphase coexistence and the diffused phase transition character were demonstrated in the 8 nm nanocrystalline BT ceramics. Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2002CB613301) and the National Natural Science Foundation of China (Grant No. 50872093)     

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.     

铁微量掺杂对二钛酸钡陶瓷介电性能的影响

采用常规固相反应法,以碳酸钡、二氧化钛和三氧化二铁为原料,制备微量铁掺杂的二钛酸钡陶瓷,研究了铁掺杂含量对二钛酸钡陶瓷的相纯度、相对密度和介电性能的影响.采用X射线粉末衍射仪检测二钛酸钡陶瓷的相成分,利用精密阻抗分析仪测量其介电性能.结果表明,微量铁元素进入了二钛酸钡晶格,能够获得单相二钛酸钡陶瓷的最大铁掺杂量在0.5%～1%之间.随着铁含量的增加,铁电相变居里温度快速减小,从未掺杂时的415 ℃降至铁含量为0.02%时的376 ℃和铁含量为0.5%时的324 ℃.同时介电常数逐渐减小,介电峰不断发生宽化,但并没有导致弛豫性铁电体的出现.微量铁元素的掺杂在实验测量误差范围内对陶瓷的密度影响不大.     

Microwave sintering of Ca0.6La0.2667TiO3 microwave dielectric ceramics

Ca0.6La0.2667TiO3 ceramics were prepared by conventional and microwave sintering techniques and their sinterability,microstruc-ture,and microwave dielectric properties were investigated in detail for comparison.Densified Ca0.6La0.2667TiO3 ceramics were obtained by microwave sintering at 1350oC for 30 min and by conventional sintering at 1450oC for 4 h.An unusual phenomenon was found that some larger grains(grain size range:8-10 μm) inclined to assemble in one area but some smaller ones(grain size range:2-4 μm) inclined to gather in another area in the microwave sintered ceramics.The microwave dielectric properties of Ca0.6La0.2667TiO3 ceramics prepared by micro-wave sintering at 1350oC were as follows:dielectric constant(εr) = 119.6,quality factor(Qf) = 17858.5 GHz,and temperature coefficient of resonant frequency(τf) = 155.5 ppm/oC.In contrast,the microwave dielectric properties of the ceramics prepared by conventional sintering at 1450oC were εr = 117.4,Qf = 13375 GHz,and τf = 217.2 ppm/oC.     

Electric characteristics of Nd_2O_3 doped BaTiO_3 ceramics

0　INTRODUCTIONBaTiO3hasbeenextensivelystudiedandwidelyuti lizedasaceramicmaterialforelectronicapplications .TheuseofadditivespermitsvaryingoftheCurietemperatureandpresentsapeculiarvariationoftheresistancewithtemperature[1,2 ] .Commonadditivesaredopantionssuchasyttrium ,whichsubstituteforbariumandpromotean typesemiconductivity .Therare earthelementsinBa TiO3ceramicscouldlowertheresistivitiy ,improvethedi electriccharacteristicsanddecreasethesinteringtempera turenoticeably[3,4 ] ,sotheim…     

Effect of SiO2 addition on the dielectric properties and microstructure of BaTiO3-based ceramics in reducing sintering

The effect of SiO2 doping on the sintering behavior,microstructure,and dielectric properties of BaTiO3-based ceramics has been investigated.Silica was added to the BaTiO3-based powder prepared by the solid state method with 0.075mo1%,0.15mo1%,and 0.3mo1%,respectively.The SiO2-doped BaTiO3-based ceramic with high density and uniform grain size were obtained,which were sintered in reducing atmosphere.A scanning electron microscope,X-ray diffraction,and LCR meter were used to determine the microstructure as well as the dielectric properties.SiO2 can form a liquid phase belonging to the ternary system of BaO-TiO2-SiO2,leading to the formation of BaTiO3 ceramics with high density at a lower sintering temperature.The SiO2-doped BaTiO3-based ce-ramics can be sintered to a theoretical density higher than 95% at 1220℃ with a soaking time of 2 h.The dielectric constants of the sample with 0.15mo1% SiO2 addition sintered at 1220℃ is about 9000.Doping with a small amount of silica can improve the sinter-ing and dielectric properties of BaTiO3-based ceramics.     

Dielectric Properties of B2O3 Doped MgTiO3-CaTiO3 System Ceramics

The dielectric ceramics with a main crystal phase of MGTiO3 and additional crystal phase of CaTiO3 were prepared by the conventional electronic ceramics technology .the strucures of MgTiO3 are ilmenitetype,and belong to hexagonal syngony.the ratio of MgTiO3 to Ca TiO3 doping on the dielectric properties of MGTiO3-CaTiO3(MCT)ceranics were inrestigated.the addition of B2O3 decreases the sintering temperatnre and results in rapid desification without obrious negative effect on the Q values of the system(Q=1/tan ).B2O3 exists as liquid phase in the sintering process,promoting the reactions as a singering agent.     

Phase Structure and Dielectric Properties of Doped BaTiO3 Ceramics

The effects of two rare earth oxides such as CeO2 and Sm2O3 on the phase structure and dielectric properties of BaTiO3 ceramic were investigated. Results indicate that the dielectric constant of this system will increase greatly with the increasing content of these two oxides, and Ce^4＋ substitutes for Ba^2＋ located at A-site in ABO3 structure. Quantitative XRD analysis shows that c/a ratio in the sample with addition of CeO2 will increase, which implies the increase of tetragonality in system, causing the augment of dielectric constant, and the decrease of the crystal＇s geometrical symmetry results in curie-temperature moving towards low temperature; Sm^3＋（0.096 nm） substitutes for Ba^2＋（0.135 nm） possessing larger radius in A-site and the electrovalency in A-site increases, the mutual effect is strengthened, so the polarization is enhanced, and the dielectric constant increases notablely.     

The Synthesis and Eleetrorheologieal Properties of BaTiO3-coated PMMA Mierospheres

Coated-PMMA microspheres consisting of poly （methyl methacrylate）（PMMA） core and barium titanate （BaTiO3） shell were synthesized by the modified sol-gel processing and then adopted as an electrorheological （ER） materials. The structure and morphology of coated powders were chyfecterized by SEM and FT-IR; the shear stress of the suspensions of coated-PMMA particles and pure PMMA particles in silicone oil with a 20 vol% were investigated. The results show that the BaTiO3 coated PMMA microspheres based suspension in silicone oil exhibited typical ER behavior and stronger ER effects.     

Dispersing and doping of BaTiO<Subscript>3</Subscript> powder by adsorption

Dispersing and doping of BaTiO3 powder by adsorption method were investigated. Ultrafine BaTiO3 powders were dispersed in the aqueous with ammoniumized citrate （NHa-CA） or ammoniumized citric lanthanum chelate （NH4-La-CA） as dispersant by ultrasonic bath. Better dispersion of BaTiO3 slurry was obtained in the aqueous with NH4-La-CA than that of NH4-CA when the mass ratio of citric acid （CA） to BaTiO3 was less than 0,007. The pH value hardly affects the dispersion property of BaTiO3 suspension dispersed by NH4-La-CA. BaTiO3 powder could be well dispersed （median size D50=0.45 μm） and also doped with high uniformity of added components by adsorbing citric acid chelate on surface. Compared with solid mixing, better microstructure and properties of La/Mn codoped ceramics were obtained by adsorption method.     

Ferroelectric properties of Bi3.4Ho0.6Ti3O12 thin films prepared by sol-gel method

We have prepared the Ho-substituted bismuth titanate (Bi_3.4Ho_0.6Ti₃O₁₂, BHT) thin films on Pt/Ti/SiO₂/Si substrates using sol-gel method. The crystal structure and morphology of the films were characterized using X-ray diffraction and atomic force microscopy. The BHT film shows a single phase of Bi-layered Aurivillius structure and dense microstructure. The 2Pr and 2Ec of the 600-nm-thick BHT film were 38.4 μC/cm² and 376.1 kV/cm, respectively at applied electric field 500 kV/cm. The dielectric constant and dielectric loss are about 310 and 0.015 at a frequency of 1 MHz, respectively. The Pr value decreased to 93% of its pre-fatigue values after 4.46×10⁹ switching cycles at 1 MHz frenquency, and the BHT film shows good insulating behavior according to the test of leakage current. Supported by the Hubei Province Natural Science Foundation (Grant No. 2007ABA309)     

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.     

The Influence of Yttrium Isopropoxide on the Mechanical Properties of SiCw-reinforced AlN Ceramics

By using self-made metal-alkoxide yttrium isopropoxide as a sintering additive and disperser of whisker, the SiC whisker reinforced AlN ceramics was prepared. Its apparent density is 99.5 percent of the theoretical density; its flexural strength and fracture toughness are 681 MPa and 5.21 MPa·m^1/2 respectively. Comparing the result with that by applying Y₂O₃ powder as a sintering additive, the flexural strength is increased by 25% and the fracture toughness is increased by 33%. The dispersity of whisker by increased yttrium isopropoxide is significantly better than that by Triton X-100. CHEN Yong-xi: Born in 1945