Sintering effect on electrical properties and pulse aging behavior of （V2O5-Mn3O4-Er2O3）-doped zinc oxide varistor ceramics

The effect of sintering temperature on microstructure, electrical properties, and pulse aging behavior of(V2 O5-Mn3 O4-Er2 O3)-doped zinc oxide varistor ceramics was systematically studied. When the sintering temperature increased, the average grain size increased from 6.1 to 8.7 m and the sintered density decreased from 5.52 to 5.43 g/cm3. The breakdown field decreased from 3856 to 922 V/cm with an increase in the sintering temperature up to 900 C, whereas a further increase to 2352 V/cm at 925 C. The nonlinear coefficient increased pronouncedly from 4.6 to 30.0 with an increase in the sintering temperature. The varistor ceramics sintered at 850 C exhibited the best clamping characteristics, with the clamp voltage ratio of the range of 2.22–2.88 for pulse current of 1–25 A. The varistor ceramics sintered at 925 C exhibited the strongest stability, with %ΔE 1 mA/cm2=–8.8% after applying the multi-pulse current of 25 A.     

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.     

Microstructure and microwave dielectric properties of Ba6-3xSm8+2xTi18O54 ceramics with various BaxSr1-xTiO3 additions

The Ba6-3xSm8+2xTi18O54 (x=2/3) microwave dielectric ceramics were prepared by traditional solid sate reaction technique. The ex-periment was based on the Ba6-3xSm8+2xTi18O54 (BST) microwave dielectric ceramics doped with a certain amount of Bi2O3, then the effects of BaxSr1-xTiO3 additives on the structure and microwave dielectric properties of Ba6-3xSm8+2xTi18O54 ceramics were investigated using X-ray diffraction and scanning electron microscopy. In this study, the small amount substitution of Sr for Ba was effective for the microwave dielec-tric properties of BST, especially the τf could be tuned to near zero. The result showed that the BST possessed excellent dielectric properties when the addition of Bi2O3 and BaxSr1-xTiO3 was 1 wt.% respectively: εr=79.6, Q?f=10789 GHz, τf=-1.5 ppm/oC.     

Sintering characteristics and microwave dielectric properties of 0.5Ca0.6La0.267TiO3-0.5Ca(Mg1/3Nb2/3)O3 ceramics prepared by reaction-sintering process

0.5 Ca_(0.6)La_(0.267)TiO_3-0.5 Ca(Mg_(1/3)Nb_(2/3))O_3(5 CLT-5 CMN) ceramics were prepared by a reaction-sintering process and their sintering characteristics, microwave dielectric properties were investigated in detail.Without any calcination stage involved,a mixture of CaCO_3, La_2 O_3, TiO_2, MgO and Nb_2 O_5 was pressed and sintered directly. Pure phase 5 CLT-5 CMN ceramics with high density and dense microstructure can be obtained after sintered at 1400 ℃ for 4 h. Compared with those prepared by the conventional ceramic route, 5 CLT-5 CMN ceramics produced by the reaction-sintering process exhibit slightly higher dielectric constant and Q×f value. Fine microwave dielectric properties of ε_r= 56.4, Q×f= 48,550 GHz and T_f = +8.7 ppm/℃ for 5 CLT-5 CMN ceramics sintered at 1400 ℃ for 4 h are obtained, suggesting reactionsintering process is a simple and efficient method to produce pure phase 5 CLT-5 CMN ceramics as a potential candidate for the fabrication of microwave devices.     

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.     

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,     

Effect of CeO_2 on low temperature pressureless sintering of porous Si_3N_4 ceramics

Porous silicon nitride(Si_3N_4) ceramics were fabricated by low temperature pressureless sintering, using carbonized rice husk and α-Si_3N_4 powders as raw materials, and MgO-CeO_2 as sintering additives. The effects of CeO_2 concentration and sintering temperature on phase composition, microstructure, porosity and flexural strength of the sintered products were investigated by X-ray diffraction(XRD), scanning electronic microscopy(SEM), Archimedes' displacement method and three-point bending strength, respectively. The results suggested that MgO-CeO_2 was a much more effective sintering additive for Si_3N_4 than MgO alone. When CeO_2 concentration was 4 wt.%–5 wt.% and sintering temperatures were in a range of 1500 to 1550 oC, the obtained porous silicon nitride ceramics had the porosity of 45.78%–42.81% and flexural strength of 49.44–84.09 MPa. Moreover, when sintering temperature was 1550 oC and CeO_2 concentration was 5%, large elongated β-Si_3N_4 grains were well developed.     

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.     

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.     

Effects of Ce3＋ , Nd3＋ , Gd3＋, Tb3＋ and Lu3＋ ions on Formation of CaCO3

The effects of lanthanides at various concentrations on CaCO3 crystal growth were studied by X-ray diffraction (XRD), infrared spectra (IR), X-ray photoelectric energy spectra (XPS) and inductively coupled plasma mtms spectrometry (ICP-MS). It was found that the calcite, a stable form of CaCO3 in thermodynamics, is the predominant species. The research indicates that lanthanide ions (Ln3 ) can partly substitute the Ca2 in the lattice of CaCO3 crystals, and change the crystal characterization and direct the ordinal growth of CaCO3 crystals.     

Photoluminescence of Dy~(3 ) Ions in Ba_3La(BO_3)_3

Dy3 isanimportantactivator .Ithasbeenexten sivelyappliedinmanyluminescentmaterials .Inre centyears ,someresearchershavestudiedthespec trumcharacteristicsofluminescentmaterialsdopedDy3 [1～ 6 ] andhaveobtainedsomemeaningfulre sults .InordertodevelopnewfluorescentmaterialsanddiscussthephotoluminescentruleofDy3 inthecomplexborate ,thispaperstudiesthephotolumines centcharacteristicsofDy3 inBa3La(BO3) 3host ,anddiscussestheinfluenceofthecharge to radiusratio(z/r)ofrareearthionRE3 andthecon…     

3-Hydroxy-3-methylglutaric aciduria: deficiency of 3-hydroxy-3-methylglutaryl coenzyme A lyase

Basic principles are offered to support the suggestion that use of special care space must be made with a mind toward prevention of obsolescence. Certain conventional design features should be examined critically and decisions made as to their applicability to the needs of a particular program.     

Dy^3＋在（LaO）3BO3和（GdO）3BO3中的光致发光

研究了Ｄｙ＾３＋在（ＬａＯ）３ＢＯ３和（ＧｄＯ）３ＢＯ３中的光致发光;探讨了基质晶体结构、稀土离子ＲＥ＾３＋的电荷半径比（Ｚ／ｒ）和Ｄｙ＾３＋含量对（Ｄｙ＾３＋）发光强度及发光颜色的影响;分析了（ＧｄＯ）３ＢＯ３中Ｂｉ＾３＋对Ｄｙ＾３＋发光的敏化作用及Ｄｙ＾３＋４Ｆ９／２→＾６Ｈ１３／２超灵敏跃迁发射的自身浓度猝灭机理。     

Ca3La(BO3)3中Dy3+的光致发光

研究了Ca3La(BO3)3基质中Dy^3 的发射光谱和激发光谱。结果表明，强的激发峰值为351nm、367nm和386nm；Dy^3 的488nm和578nm发射的最佳浓度均为xDy=0．03；Dy^3 发射的黄光和蓝光强度比(用Y／B表示)随Dy^3 浓度的增加而逐渐增大；Dy^3 的^4F9/2→^6H15/2、^6H13/2跃迁发射的浓度猝灭机理均为电偶极-电偶极相互作用；同时还探讨了Ce^3 对Dy^3 发光的敏化作用。     

K3AlF6-Na3AlF6-AlF3铝电解体系密度的研究

采用流体静力称重法研究了K<,3>AlF<,6>-Na<,3>AlF<,6>-AlF<,3>铝电解质体系的密度.探讨了K<,3>AlF<,6>,AlF<,3>含量和温度与K<,3>AlF<,6>-Na<,3>AlF<,6>-AlF<,3>体系密度的关系.实验结果表明:K<,3>AlF<,6>-Na<,3>AlF<,6>-AlF<,3>体系密度与温度成较好的线性关系,温度升高,密度降低;随着AlF<,3>含量的降低,体系的密度对温度的变化更加敏感.相同过热度下,固定KR(钾冰晶石含量),随着AlF3含量的增加,体系的密度呈现出不同的变化规律,相同过热度条件下,对于较低的KR=0.1值,随着AlF<,3>含量的增加,体系的密度逐渐下降,对于较高的KR=0.5值,随着AlF<,3>含量的增加,体系密度先降低后增加,存在最低点.相同过热度下,固定AlF<,3>含量,随着KR增加,体系密度也呈现出不同的变化规律,当AlF<,3>为22%,随着KR增大,体系密度变化不大;当AlF<,3>为26%,30%,随着KR增大,体系密度先降低后增加.     

Optical Spectroscopy of Er^3＋ and Er^3＋/Yb^3＋ Co-doped Bi2O3-GeO2-B2O3-ZnO Glasses

The （60 - x）Bi2O3 - xGeO2-30B2O3-10ZnO （x = 5, 10, 20, 30 molar percent） glasses doped with Er^3＋ and Er^3＋/Yb^3＋ were fabricated using the melting method. The thermal stability of the glasses was studied with their DTA curves. The results show that the difference between the glass transition temperature and the crystallization onset temperature increases with the increase of GeO2 content, indicating that the thermal stability of the glass has become better. The absorption spectra were recorded and the stimulated emission cross sections were calculated using the McCumber theory. The Ω2, O4, and Ω6 parameters,the transition probability, the radiative lifetime, and the fluorescence branch ratio of Er^3＋ for optical transition were calculated from their absorption spectra in terms of reduced matrix U^（t）（λ = 2, 4, 6） character for optical transitions. The infrared emission of Er^3＋ was measured upon excitation with 970 nm light and the full width at half-maximum （FWHM） was estimated from the emission spectra. The pumping efficiency and the intensity of the emission at the 1.54 μm band of Er^3＋ were enhanced considerably by co-doping Yb^3＋ .     

Enhanced ultraviolet upconversion in YF3：Yb^3＋/Tm^3＋ nanocrystals

Unusual intense infrared-to-ultraviolet upconversion luminescence was observed in YF3:Yb3+(20%)/Tm3+(1%) nanocrystals under 980 nm excitation. The intense ultraviolet emissions (1I6→3H6, 1I6→3F4, and 1D2→3H6) were affirmed arising from the excitation processes of five-photon and four-photon. In comparison with the bulk sample with the same chemical compositions, ultraviolet upconversion lumi-nescence of the nanocrystals was markedly enhanced. Spectral analysis indicated that the enhancement was attributed to the decrease of Judd-Ofelt parameter Ω2, which precluded the transition rate from 3F2 to 3F4, enhanced the energy transfer process and populated the 1D2 level: 3F2→3H6 (Tm3+): 3H4→1D2 (Tm3+).