Study on Ferroelectric and Dielectric Properties of La-Doped CaBi4Ti4O15-Based Ceramics

Research on bismuthlayer structuredferroelectricceramics as piezoelectric material with high Curie tem-perature ,strong anisotropic characters ,lowdielectricdissipationfactor and lowaging rate has attracted in-creasing interest[1,2].It can be used to manu…     

Effects of Interlayer Composition on Bond Strength and Interfacial Microstructure of Green Joined CePO4－ZrO2 Ceramics

Effects of interlayer composition on bonding strength and inteffacial microstructure of green joined CePO4-ZrO2 ceramics were studied. Green bodies of 25% CePO4/ZrO2 and ZrO2 ceramics were joined by using interlayer composed of CePO4 and ZrO2 at 1450℃ for 120min without applied pressure. The effects of CePO4/(CePO4 ZrO2) ratio on the bond strength of the joints were investigated. Under the experimental conditions, the grain size of the particles grown in the joint is smaller than those in joined ceramics. The microstructure of the joint is more homogeneous than that of the matrix and without obvious cracks, pores and other defects.     

Effect of Y2O3, CeO2 on Sintering Properties of Si3N4 Ceramics

The effect of rare earth oxides Y203 or Ce02 on sintering properties of Si3N4 ceramics was studied and the mechanism of assisting action during sintering was analyzed. The results in dicate that the best sintering properties appear in Si3N4 ceramics with 5% Y203 or 8% CeO2. Secondary crystallites are formed at grain boundaries after heat treatment,which decreases the amount of glass phase and contributes to the improvement of high-temperature mechanical properties of silicon nitride.     

Investigation on Ductile Property of CePO4 Ceramic

Amajorimpedimentforengineeringapplicationsofceramicsistheirbrittlenesswhichoftenrendersthemdifficultandcostlytomachine .Tothisend ,muchefforthasgoneintothedesignofmachinablece ramicswhichcontainweakinterfaces .Ceriumphos phatehasbeenrecentlysuggestedasapotentialcom ponentinsomeoxideceramicstoimprovethemachin abilityandsecurityinuse[1,2 ] .ThecharacteristicsofCePO4 thatmakesitbeappealedforthispurposearethefollowing :thelowfractureenergyoftheinterfacebetweenitandseveralotheroxides (Al2 O3,ZrO…     

Dry Friction and Wear Characteristics of Rare-Earth/MoSi_2 Composite

MolybdenumDisilicide (MoSi2 )intermetallicspossessesmetallic likeandceramic likeproperties .Studyonitsfrictionandwearcharacteristicshasim portanttheoreticalandpracticalsignificance[1～ 5] .ItisusefultoreinforcetheMoSi2 materialbyusingthesec ondphaseforimprovementofthefrictionandwearcharacteristics[3 ,6] .Hawketal.[3 ] comparedthewearresistanceofMoSi2 withthatofMoSi2 Nbcomposites ,Nb ,aluminides (Fe3 Al,TiAl)andoxidationceramics(Al2 O3 andPS ZrO2 ) ,andfoundthatthewearresis tanceofMoS…     

Fluorescence Effect of SrAl2O4:Eu and Diffuse Reflectivity of SrAl2O4:Eu Based Ceramics

SrAl2O4:Eu was adopted as main phase to prepare the ceramic pumping cavity material with ultraviolet(UV) converting function in order to match with laser absorption spectra. The relationship between SrAl2O4:Eu powder processing and fluorescence effect was studied. The glass material with lower refractive index was added to the SrAl2O4:Eu based ceramics. The diffusive reflectivity and the influence of fluorescence effect on reflection spectra of the ceramics were investigated. Some experimental results can be used for evaluating technical feasibility of the SrAl2O4:Eu based ceramics used for laser reflectors.     

Impedance Characteristics of MgO-ZrO2 Ceramics Doped with CeO2

The ultrafine CexMg0.06Zr1-xO1.94 （ x = 0 16% ） powders were synthesized by a chemical co-precipitated method. The pressed compacts were sintered in air at 1300, 1400, 1500, 1600℃ for 3 h, respectively. The phase of the ceramics was characterized by the X-ray diffraction （XRD） method. The conductivity of the ceramics was measured by the AC complex impedance technique at 700- 1200 ℃. The ratio of the cubic phase in the ceramics improves with increasing CeO2 content, leading to a enlargement of the oxygen ionic migration channel. The contact resistance between conductive phase particles decreases with increasing CeO2 content, leading to a lower migration hindrance of the oxygen ionic. Consequently, the ionic conductivity of the ceramics improves with increas- ing CeO2 content. Additionally, an analysis for this phenomenon was also presented.     

Impedance Characteristics of MgO-ZrO_2 Ceramics Doped with CeO_2

Impedance Characteristics of MgO-ZrO_2 Ceramics Doped with CeO_2     

Effect of La2O3 on Microstructure and Transmittance of Transparent Alumina Ceramics

Optically transparent alumina ceramics were fabricated by conventional process and sintered without pressure in H2 atmosphere. The results indicate that relative densities of alumina specimens increase to theoretical densities （T. D. ） with increasing content of La2O3. With increasing holding time during sintering, much less pores and larger grains were found in the sintered alumina samples. Higher transmittance was achieved in alumina codoped with MgO and La2O3 as compared with that doped with MgO only. The total-transmittance of alumina sample is up to 86% at twavelength range of 300 - 800 nm.     

Preparation and Upconversion Luminescence of Y3Al5O12∶Yb3+, Er3+ Transparent Ceramics

YAG:1% (atom fraction) Yb3 , 0.5% (atom fraction) Er3 transparent ceramics were fabricated by the solid state reaction method using high-purity Y2O3, Al2O3, Yb2O3, and Er2O3 powders as starting materials. The mixed powder compact was sintered at 1760 ℃ for 6 h in vacuum and annealed at 1500 ℃ for 10 h in an air atmosphere. The ceramics consisted of about 10 μm grains and exhibited a pore-free structure. The optical transmittance of the ceramics at 1064 nm was nearly 80%. Upconversion emissions were investigated on the ceramics pumped by a 980 nm continuous wave diode laser, and strong green emission centered at 523 and 559 nm and red emission centered at 669 nm were observed, which originated from the radiative transitions of 2H11/2→4I15/2, 4S3/2→4I15/2, and 4F9/2→4I15/2 of Er3 ions, respectively.     

Properties of La2O3-Doped PNSZT Piezoelectric Ceramics Having Tetragonal and Rhombohedral Coexistent Phases

The relationship between composition and the electric mechanical properties for La2O3-doped lead niobium stibium zirconate titanate(La2O3-doped PNSZT) piezoelectric ceramics,in which there are tetragonal and rhombohedral coexistent phases, was studied. A series of piezoelectric ceramics with good properties was obtained, having dielectric constants(ε=1500～2500), plane electromechanical coupling factor(Kp=0.45～0.65), mechanical quality factor(Qm=500～1600). These materials are used for making ultrasonic sensor and filter, and marine acoustic launching and receiving device, and so on. It has been explored that the influence of composition on the lattice constant and phase composition of La2O3-doped PNSZT piezoelectric ceramics by XRD(X-ray diffraction). The character of dielectric constant changing of La2O3-doped PNSZT piezoelectric ceramics before polarization and after polarization was studied. The affecting mechanism about composition on the electric machine properties of phase coexistent La2O3-doped PNSZT piezoelectric ceramics was analyzed and discussed.     

Effect of La2O3-Dopant on Microstructure and Microwave Dielectric Properties of CaO-MgO-Nb2O5-TiO2 System Ceramics

With the development of microwave integratedsystem for wireless communication, requirements ofthe microwave device are combined with high dielec tric constants (εr), low dielectric losses (Q = 1/tanδ) and near zero temperature coefficient for stabili ty and frequency selectivity[1,2]. But it is hard to findmaterials that satisfy all above mentioned requiredcharacteristics. In general, a ceramic with a high di electric constant has a larger positive temperature coef fi…     

Preparation and Luminescence of Er^3＋ Doped Oxyfluoride Glass Ceramics Containing LaF3 Nanocrystals

Er^3＋ doped transparent oxyfluoride glass ceramics version and near infrared luminescence behavior of Er^3＋ in containing LaF3 nanocrystals were prepared and the up-conglasses heat-treating time and temperature, the size （varied from 0 to 19 and glass ceramics were investigated. With increasing nm） and crystallinity （varied from 0 to 47%） of LaF3 nanocrystals in the glass ceramics are increased. The up-conversion luminescence intensity of Er^3＋ ions in the glass ceramics is much stronger than that in the glasses The near infrared emission of Er^3＋ ions in and increased significantly with increasing heat-treating time and temperature the glass ceramics is found to be similar to that in the glasses.     

Fabrication of Transparent Polycrystalline Yttria Ceramics by Combination of SPS and HIP

Transparent polycrystalline yttria is a promising optical ceramics with excellent physical and chemical properties. A commercial yttria powder with a mean particle size of 1.0 μm and narrow size distribution was selected as the starting material. Transparent polycrystalline yttria ceramics without any additives were successfully prepared by hot isostatic pressing (HIP) at 1700 ℃ for 2 h under the pressure of 200 MPa in Ar following spark plasma sintering (SPS). The as-prepared specimens consist of uniform grains of ～40 μm. Scanning electron microscopy (SEM) images show their pore-free structure. The influences of the yttria powder and sintering process on the properties of the yttria ceramics, including the microstructure and optical properties, were further investigated in our study.     

Preparation and Upconversion Luminescence of Y3Al5O12 ： Yb^3＋ , Er^3＋ Trapsparent Ceramics

YAG： 1% （atom fraction） Yb^3＋ , 0.5% （atom fraction） Er3＋ transparent ceramics were fabricated by the solid state reaction method using high-purity Y2O3, Al2O3, Yb2O3, and Er2O3 powders as starting materials. The mixed powder compact was sintered at 1760 ℃ for 6 h in vacuum and annealed at 1500 ℃ for 10 h in an air atmosphere. The ceramics consisted of about 10μm grains and exhibited a pore-free structure. The optical transmittance of the ceramics at 1064 nm was nearly 80%. Upconversion emissions were investigated on the ceramics pumped by a 980 nm continuous wave diode laser, and strong green emission centered at 523 and 559 nm and red emission centered at 669 nm were observed, which originated from the radiative transitions of ^2H11/2→^4I15/2, ^4S3/2→^4I15/2, and ^4F9/2→^4I15/2 of Er^3＋ ions, respectively.     

Effect of Additive on Microstructure of Transparent YAG Ceramics

Crystallineyttriumaluminumgarnet (Y3 Al5O12 )isanimportantlasermaterialduetoitssuperioropti calandmechanicalproperties[1,2 ] .NeodymiumdopedYAGisusedwidelyaslaserhostmaterialinvarioussolidstatelasers .SingleYAGcrystalsaregenerallysynthesizedbyCzochralskim…     

Preparation of MachinableY—TZP／LaPO4 Composite Ceramics byLiquid Precursor Infiltration

Ｃｅｒａｍｉｃｍａｔｅｒｉａｌｓｈａｖｅｂｅｅｎｕｓｅｄａｓｅｎ ｇｉｎｅｅｒｉｎｇｍａｔｅｒｉａｌｓｂｅｃａｕｓｅｏｆｔｈｅｉｒｈｉｇｈｓｔｒｅｎｇｔｈａｎｄｈｉｇｈｈａｒｄｎｅｓｓ .Ｔｈｅｄｉｓａｄｖａｎｔａｇｅｏｆｓｕｃｈｃｅｒａｍｉｃｓｉｓｔｈｅｄｉｆｆｉｃｕｌｔｙｉｎｍａｃｈｉｎｉｎｇａｆｔｅｒｓｉｎｔｅｒｉｎｇ ,ｗｈｉｃｈｌｅａｄｓｔｏｈｉｇｈｍａｃｈｉｎｉｎｇｃｏｓｔ.Ｔｏｄｅｃｒｅａｓｅｉｔ ,ｖａｒｉｏｕｓｃｅｒａｍｉｃｓｗｉｔｈｒｅａｓｏｎａｂｌｅｍａｃｈｉｎａｂｉｌｉｔｙ ,ｃａ…     

Gaseous Penetration of Pr into PbTiO3 Ceramics and Their Electric Properties

PbTiO3ceramicsisatypicalferroelectricmaterialwithperovskitestructure .TheuniquepropertiesofPbTiO3ceramicsmakeitusefulforavarietyofappli cations .Forexample ,itisaverygoodcandidateforpiezoelectricapplicationsathigh temperatureinhighsensibility[1,2 ] .Inrecentyears ,studiesondopedPbTiO3ceramicshavereceivedconsiderableattention .ThemodifiedPbTiO3ceramicsdopedwithCa2 ,Sm3 ,Y3 etcimprovedpropertiesincludingreducedCuriestemperature ,degradedtetragonaldistortionde greeandimprovedprocessabil…     

Nonlinear behavior of Tb4O7-modified ZnO-Pr6O11-based ceramics with high breakdown field

The effect of Tb4O7 on electrical behavior of the ZnO-Pr6O11-based varistor ceramics was investigated.Microstructural analysis indicated that the addition of Tb4O7 decreased average grain size from 3.6 to 3.2 μm and increased the sintered density from 5.58 to 5.68 g/cm3.As the amount of Tb4O7 increased,the breakdown field increased from 9393 to 12437 V/cm and the nonlinear coefficient increased from 50 to 65.The varistor ceramics added with 0.5 mol.% in the amount of Tb4O7 exhibited an excellent stability by exhibiting-0.1% in the variation rate of the breakdown field,0% in the variation rate of the nonlinear coefficient,and 8.8% in the variation rate of the leakage current density for DC-accelerated aging stress of 0.85 E1 mA/115℃/24 h.     

Studies and Properties of Ceramics with High Thermal Conductivity

The sintering technology of the AlN ceramics power were discussed. It is discussed that the compound sintering aids is consistent with the enhancement of the the thermal conductivity of AlN ceramics, and sintering technics is helped to the improvement of density. It is analyzed how to sinter machinable AlN ceramics with high thermal conductivity. And the microstructure of compound ceramics based on AlN was studied.