Sintering effect on ageing behavior of rare earths （Pr6O11-Er2O3-Y2O3 ）-doped ZnO varistor ceramics

The electrical properties and ageing behavior of the rare earths (Pr6O11-Er2O3-Y2O3)-doped ZnO varistor ceramics were systematically investigated at sintering temperature range of 1335-1350°C. With an increase in the sintering temperature, the sintered density increased from 5.41 to 5.64g/cm3 and the average grain size increased from 5.8 to 7.9μm. The varistor properties and ageing behavior were significantly affected by small sintering temperature range of 1335-1350°C. The breakdown field noticeably decreased from 5767 to 3628V/cm with an increase in the sintering temperature. The varistor ceramics exhibited the highest nonlinear coefficient (43.2) at the sintering temperature of 1340°C. The varistor ceramics sintered at 1350°C exhibited a surprisingly excellent stability by exhibiting 0.3% in the variation rate of the breakdown field and 0.3% in the variation rate of the nonlinear coefficient for ageing stress of 0.95 E1mA/150°C/24 h.     

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.     

Highly nonlinear property and threshold voltage of Sc2O3 doped ZnO-Bi2O3-based varistor ceramics

A series of ZnO-Bi2O3-based varistor ceramics doped with 0-0.4 mol.% Sc2O3 were prepared by high-energy ball milling and sintered at temperatures between 1000 and 1150oC. X-ray diffractometry (XRD) and scanning electron microscopy (SEM) were applied to characterize the phases and microstructure of the varistor ceramics. A DC parameter instrument for varistor ceramics was applied to investigate the electronic properties and V-I characteristics. The results showed that there were no changes in crystal structure with Sc2O3-doped varistor ceramics and that the average size of ZnO grain increased first and then decreased. The best electronic characteristics of the varistor ceramics prepared by high-energy ball milling were found in 0.3 mol.% Sc2O3-doped ZnO-Bi2O3 -based ceramics sintered at 1000 oC, which exhibited a threshold voltage of 821 V/mm, nonlinear coefficient of 62.1 and leakage current of 0.16 μA.     

Sintering behavior and microwave dielectric properties of （1-x）CaTiO_3-xLaAlO_3 ceramics

The sintering behavior,microstructure and microwave dielectric properties of (1–x)CaTiO3–xLaAlO3 (x=0.1,0.3,0.5,0.7,0.9,respectively) ceramics were investigated systematically by thermogravimetry-differential thermal analysis (TG-DSC),X-ray diffraction (XRD),scanning electron microscopy (SEM) and a network analyzer.The result showed that forming temperature of the perovskite type crystal increased with increasing of x value.0.9CaTiO3-0.1LaAlO3 ceramics were sintered well from 1 400 to 1 550 oC,its bulk density increased with sintering temperature,and microwave dielectric properties of the ceramics at 1 400 oC was shown as follows: relative dielectric constant εr= 45.1,Q×f= 46 087 GHz and τf=–14.1×10–6/oC,respectively.But 0.7CaTiO3-0.3LaAlO3 ceramics were sintered well only when sintering temperature rose to 1 500 oC.(1–x)CaTiO3–xLaAlO3 (x=0.5,0.7 and 0.9,respectively) were not sintered well up to 1 550 oC and the sintered samples exhibited porous characteristic and with low bulk density.     

Microstructure,electrical and dielectric properties,and aging behavior of ZPCCA varistor ceramics with Er2O3 doping

The microstructure, electrical and dielectric properties, and DC-accelerated aging of the ZPCCA(ZnO-Pr6O11-CoO-Cr2O3-Al2O3) ceramics were investigated with various contents of Er2O3. The ceramic phases consisted of a bulk phase of ZnO grains, and a minor secondary phase of mixture of Pr6O11 and Er2O3. The increase of the content of doped Er2O3 increased the densities of sintered pellet from 5.66 to 5.85 g/cm3, and decreased the average grain size from 9.6 to 6.3 μm. With the increase of the content of doped Er2O3, the breakdown field increased from 2390 to 4530 V/cm, and the nonlinear coefficient increased from 28.4 to 39.1. The sample doped with 0.25 mol.% Er2O3 exhibited the strongest electrical stability; variation rates for the breakdown field measured at 1.0 mA /cm2, and for the non-ohmic coefficient were –3.4% and –23.8%, respectively, after application of a stress of 0.95 EB/125 ℃/24 h.     

Microstructure and Electrical Properties of Er2O3-Doped ZnO-Based Varistor Ceramics Prepared by High-Energy Ball Milling

The microstructure, electrical properties and density of ZnO-based varistor ceramics with different Er2O3 content prepared by high-energy ball milling （HEBM） and sintered at 800℃ were investigated. With increasing Er2O3 content, the ZnO grain size decreases due to the Er-rich phases inhibiting grain growth ; and nonlinear coefficient （ α ） decreases because of the decrease of barrier height （φB） The breakdown voltage （Eb） and density increase, whereas leakage current （IL） decreases with increasing Er2O3 content. The barrier height （φB）, donor concentration （Nd）, density of interface states （Ns） decrease and barrier width （ω） increases with increasing Er2O3 content due to acceptor effect of Er2O3 in varistor ceramics.     

Electrical Properties and Applications of （ZrO2）0.92 （Y2O3）0.08 Electrolyte Thin Wall Tubes Prepared by Improved Slip Casting Method

8%(mole fraction) yttria-stabilized zirconia electrolyte thin wall tubes were prepared by improved slip casting method. The length and wall thickness of the tubes are 266 mm and 0.4 - 0.9 mm, respectively and the relative density is 96.7 %. The microstructure and electrical properties of samples sintered at different temperatures were studied using SEM and ac impedance spectroscopy. The effect of sintered density, grain and grain boundary on the electrical properties of the samples was analyzed. The research results show that the density of the samples increases gradually with increasing sintering temperatures. The microstructurc of samples strongly influences its electrical properties, and the electrical prop.erties of samples enhance with the increase of sintered density. The ionic conductivity of grain and grain boundary is increased as the sintering temperature increases. Better sinterability of the samples was obtained at the sintering temperature of 1650℃. The maximum open circuit voltage and short circuit current for single cell is 0.946V and 1.84A, respectively. The maximum output power of single cell is 0.46W at the temperature of 850℃.     

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.     

Study on Agglomeration and Densification Behaviors of Gadolinium-Doped Ceria Ceramics

By synthesizing reactive powders via a self-sustaining combustion synthesis, the glycine-nitrate process, the gadolinium-doped celia （GDC） with the chemical formula Ce0.8Gd0.2O1.9 was prepared. The resultant powders were dispersed with the terpineol as the dispersant through different methods such as ball milling and high-shear dispersing. Coagulation factor （CF） was used to mark the degree of agglomeration on the nano-scale GDC in this work. The effect of agglomeration on the densification behavior at different sintering temperatures was investigated. The studies indicated that agglomeration retarded the densification at the sintering stage. The powders with better dispersion exhibited a higher sintered density at the same temperature. After effective dispersion treatment, GDC could be fully densified at the sintering temperature of 1300 ℃. The densification temperature was significantly lower than those reported previously. The high sintering kinetics of the ceramics was obtained based on the agglomeration control.     

Synthesis of Al2O3/TiCN-0.2%Y2O3 Composite by Hot Pressing

Al2O3/TiCN composites were synthesized by hot pressing.The influences of components and HP temperature on mechanical properties,such as bending strength,breaking tenacity and Vickers hardness were investigated.The results showed that the mechanical properties of Al2O3/TiCN composite increased with temperature when hot pressing temperature is below 1650 ℃.The mechanical properties reached their maximums when the composites were sintered at 1650 ℃ for 30 min under hot pressing pressure of 35 MPa,the value of bending strength,breaking tenacity and Vickers hardness was 1015 MPa,6.89 MPa·m1/2,and 20.82 MPa,respectively.When hot pressing temperature was above 1650 ℃,density decreased because of decomposition with increased temperature,and mechanical properties dropped because of rapid growth of grains in size at high temperature.Microstructure analysis showed that the addition of Y2O3 led to the formation of YAG phase so as to inhibit the growth of crystals.This helped to improve breaking tenacity of the composites.TiCN particles with diameters of 1 μm dispersed at Al2O3 grain boundaries,inhibited grain growth and enhanced mechanical properties of the composites.SEM study of the propagation of indentation cracks showed that the bridge linking behavior between matrix and strengthening phase might lead to the formation of the coexisted field of crack deflection,branching and bridge linking.The mechanism of this phenomenon was that the addition of Y2O3 improved the dispersion of TiCN particles so as to enhance the tenacity of the composites.The breaking tenacity was changed from 5.94 to 6.89 MPa·m1/2.     

Effects of MgO on Properties of La2O3-TiO2 Ceramics

The influence of MgO on sintering and dielectric properties of La2O3-TiO2 ceramics was investigated, and the mechanism also discussed. The results show that La2O3-TiO2 ceramics with MgO can be sintered between 1200 and 1280 ℃. With the increasing of the MgO, the dielectric constant of the material decreases, but the temperature coefficient of dielectric constant increases. Between 1 and 40 MHz,     

Low temperature sintering behavior of La-Co substituted M-type strontium hexaferrites for use in microwave LTCC technology

The La-Co substituted Sr_(1–x)La_xFe_(12–x)Co_xO_(19)(x=0–0.5) ferrites with appropriate Bi_2O_3 additive were prepared by conventional sintering method and microwave sintering method at low sintering temperatures compatible with LTCC(low temperature co-fired ceramics) systems, and their sintering behavior was chiefly investigated, including the crystal structure, saturation magnetization Ms, magnetic anisotropy field H a, intrinsic coercivity H ci, and Curie temperature T C. Experiment results clearly showed that the pure M-type crystal phase was successfully obtained when the La-Co substitution amount x did not exceed 0.3. However, the single M-type phase structure transformed to multiphase structure with further increased x, where the M-type phase coexisted with the non-magnetic phase such as α-Fe_2O_3 phase, La_2O_3 phase, and La CoO_3 phase. Appropriate La-Co substitution improved the Ms(62 emu/g), Ha(1400 k A/m), and Hci(320 k A/m) for the ferrites with x varying from 0.1 to 0.3, but the T C decreased with increasing substitution amount. Moreover, the microwave sintered ferrites could provide larger H ci and similar Ms compared with the conventional sintered ferrites.     

Synthesis and sintering of samarium rich SmS_x and its electrical property

Non-stoichiometric samarium monosulfide(SmS_x, 0.55≤x≤1.2) was synthesized from Sm_2S_3 and SmH_3 at 1273 K for 3 h under vacuum. The influence of reaction ratio of Sm_2S_3 to SmH_3 on the fabrication of SmS_x was investigated. The fabrication of SmS required the molar ratio of Sm_2S_3 to SmH_3 above 1. Lattice parameter of synthetic SmS_x increased firstly and then decreased to saturate following with the addition of SmH_3 content. SmS_x compact was sintered at 1373 K by spark plasma sintering. Density of synthetic SmS_x was about 99% of theory density. Seebeck coefficient of n-type semiconductor Sm Sx decreased as temperature rose. The absolute value was distributed between 170–280 μV/K. The electrical resistivity of SmS_x(0.86≤x≤1.07) decreased with temperature increasing and showed similar temperature dependence. The surplus Sm which randomly distributed in the SmS_x(0.55≤x≤0.75) matrix led to a remarked reduction of electrical resistivity. The optimized power factor for SmS_(0.6) and Sm S_(0.75) could reach 1500 μW/(K~2·m) at 600 K.     

Surface reactive species on MnOx（0.4）-CeO2 catalysts towards soot oxidation assisted with pulse dielectric barrier discharge

MnOx(0.4)-CeO2 was investigated for soot oxidation assisted with a pulse dielectric barrier discharge(DBD).The catalysts were evaluated and characterized with TPO(temperature programmed oxidation),X-ray diffraction(XRD),Raman and X-ray photoelectron spectroscopy(XPS).The ignition temperature Ti for soot oxidation decreased from 240.8 to 216.4 oC with the increase of the pulse DBD frequencies from 50 to 400 Hz,lower than that of the case without pulse DBD present(253.4 oC).The results of XRD,Raman and XPS agreed well with the TPO activities of MnOx(0.4)-CeO2 towards soot oxidation.More solid solution of ceria and manganese,and surface reactive species including O2–,O– and Mn4+ were responsible for the enhancement of soot oxidation due to pulse DBD injection in the present study.For solid solution favors to the activation and transformation of those species,which are believed to be involved in the soot oxidation in a hybrid catalysis-plasma.     

Improvement in structure and superconductivity of YBa_2Cu_3O_(6+δ) ceramics superconductors by optimizing sintering processing

Polycrystalline YBa_2Cu_3O_(6+δ) bulks were synthesized by sol-gel method. Sintering processing played a vital role in the evolution of phase structure and microstructure, and thus significantly influenced their superconducting properties. The influence of calcination temperature, sintering temperature, on the bulks structure, morphology and superconducting behaviors were investigated. The results showed that the oxygen content drastically increased with calcination temperature and sintering temperature. The SEM images revealed that the grains grew up monotonously with increase of calcination temperature. With increased calcination and sintering temperature, the resistivity was reduced gradually and the superconducting properties increased. Moreover, it was found that the optimal superconducting properties(with the highest superconducting transition temperature T_c~(onset) and the narrowest transition width ΔT) were obtained at calcination temperature of 900 °C and sintering temperature of 950 °C.     

High-temperature thermal properties of yttria fully stabilized zirconia ceramics

In this study,the dependences of yttria content,porosity and grain size on the thermal properties of Y2O3 stabilized ZrO2 (YSZ) ceramics were investigated.YSZ ceramics were synthesized by the solid state reaction method.The phase,microstructure and thermal properties of YSZ ceramics were characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM),differential scanning calorimetry (DSC) and laser-flash apparatus (LFA),respectively.The results indicated that the specific heat capacity of YSZ increased with the increase of temperature and decreased with the increase of yttria content.As the temperature increased,the thermal diffusivity and conductivity of YSZ ceramics were decreased,whereas their variations for 16YSZ,18YSZ and 20YSZ were much less pronounced than those for 12YSZ and 14YSZ.At a given temperature,the thermal conductivity of YSZ was opposite to yttria content.The thermal conductivity of YSZ ceramics almost linearly decreased with the increase of porosity.In addition,the grain size also had a great influence on the thermal conductivity.     

Influence of Composition on Properties of Medium Temperature Sintering （Ba, Sr）TiO3 Series Capacitor Ceramics

The influence of the composition (Yb2O3, MgO, CeO2, Li2CO3) on the dielectric properties of medium temperature sintering (Ba,Sr)TiO3(BST) series capacitor ceramics was investigated by means of conventional technology process and orthogonal design experiments. The major secondary influencing factors and the influencing tendency of various factor′s levels for the dielectric properties of BST ceramics were obtained. The optimum formula for maximum dielectric constant (ε) and for minimum dielectric loss (tanδ) was obtained under the experimental conditions. The BST ceramics with optimum comprehensive properties was obtained by means of orthogonal design experiments, with the sintering temperature at 1200 ℃, the dielectric constant 5239, the dielectric loss 0.0097, withstand electric voltage over 6 MV·m-1, capacitance temperature changing rate (ΔC/C) -75.67%, and suited for Y5V character. The mechanism of the influence of various components on the dielectric properties of medium temperature sintering BST ceramics was studied, thus providing the basis for preparation of multilayer capacitor ceramics and single-chip capacitor ceramics.     

Microwave assisted synthesis,sinterability and properties of Ca-Zn co-doped LaCrO_3 as interconnect material for IT-SOFCs

The interconnect materials La0.7Ca0.3Cr1-xZnxO3-δ(x=0,0.01,0.03,0.05,0.07) were prepared by a microwave assisted sol-gel auto-ignition process.The crystalline structures of the samples were characterized by X-ray diffraction(XRD) and the lattice parameters were evaluated with Rietveld method.For Ca-Zn co-doped LaCrO3 with x=0.03,the sintering activity was improved,and the relative density came up to 96.5% for the sample sintered at 1300 oC for 10 h.The electrical conductivity of the samples was increased from 21.1 S/cm to the maximum of 70.9 S/cm at 650 oC in air,with the x content increasing from 0.01 to 0.03.However,with x further increasing,the electrical conductivity was decreased.The average thermal expansion coefficient(TEC) of the samples at RT-1000 oC in air was ca.10.0×10-6 K-1.All data indicated that the La0.7Ca0.3Cr1-xZnxO3-δ series ceramics would be potential candidate to be used as an interconnect materials for IT-SOFCs.     

Structure and permanent magnetic properties of SmFex （x=3-8） melt spun ribbons during heat treatment

Compounds with the composition SmFex（x=3–8） were prepared by melt spun method at a velocity of 40 m/s and subsequent annealing at temperature between 600–1000 ℃. The crystal structures of the as-quenched and as annealed powders were investigated by XRD methods with following Rietveld analysis. The glass forming ability could be enhanced by the increase of Sm content to x≤5.Metastable Sm5Fe17-type structure existed when 3≤x≤5 and temperature was lower than 800 ℃. SmFe2-type structure could be stable up to 1000 ℃ when x〉3 and temperature was under 800 ℃. The content of SmFe2-type decreased with the increase of x value and increased with temperature lower than 800 ℃, from which SmFe2-type started to bring the transition to SmFe3-type. As for Sm5Fe17-type compounds with x=3.4, the highest coercivity of 33.6 kOe could be obtained under a velocity of 30 m/s and heat treated under 700 ℃×1h.     

Preparation of transparent Y2O3 ceramic by slip casting and vacuum sintering

In the present work transparent Y2O3 ceramics were made by slip casting and vacuum sintering of nanopowders with sodium poly-acrylic acid(PAA-Na) as dispersant.The rheological properties of Y2O3 nanopowder slurry were investigated using different amounts of dis-persant and solid contents.The microstructures and transmittance of the sintered ceramics were also studied by means of scanning electron microscopy(SEM) and ultra-violet visible spectrometry.The results showed that rheological behaviors of the Y2O3 nanopowder slurry were effectively promoted by sodium polyacrylic acid.Highly dispersive and stable slurries were obtained as the dispersant was added over 1.0 dwb% under the fixed conditions of pH 11 and 45 wt.% solid content.All the slip cast green bodies were sintered into highly dense ceramics after sintering at 1700 oC for 5 h in vacuum,wherein the sample added with 1.1% sodium polyacrylic acid exhibited the highest relative den-sity of 99.36% and transmission of 30% at 800 nm wavelength.