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1.
Shu-Ting Kuo Wei-Hsing Tuan Yeh-Wu Lao Chung-Kai Wen Huey-Ru Chen 《International Journal of Applied Ceramic Technology》2009,6(2):223-230
In the present study, Pt or AgPd metal is used as the inner electrode for Bi2 O3 -doped ZnO multilayer varistors (MLV). The growth of the ZnO grains is constrained by the presence of the inner electrodes. The Pt inner electrodes are chemically inert to Bi2 O3 -doped ZnO. The Bi2 O3 could react with Pd to form PdBi2 O4 . The Bi2 O3 -rich liquid also tends to wet the AgPd electrode. The size of ZnO grains in the MLV/AgPd specimen is larger. The ZnO grains in the MLV/AgPd specimen can even grow to a size larger than the layer thickness at the expense of electrode continuity. 相似文献
2.
In this study, (Zn,Mg)TiO3+ x +Bi2 O3 +Sb2 O5 multilayer ceramic capacitors (MLCCs) with different proportions of a silver (Ag)–palladium (Pd) mixture acting as the inner electrode were sintered at 925°C for 2 h to evaluate the effect of the inner electrode on reliability. The main results reveal that the lifetime is inversely proportional to the Ag content in the Ag/Pd inner electrode. Ag diffusion into the (Zn,Mg)TiO3+ x +Bi2 O3 +Sb2 O5 MLCC during cofiring at 925°C for 2 h and Ag migration at 140°C against 200 V are both responsible for the short lifetime of the (Zn,Mg)TiO3+ x +Bi2 O3 +Sb2 O5 MLCC, particularly the latter factor. A Bi,Sb-rich secondary phase was present at the triple junction and a small amount of Ag was detected from the second phase for a (Zn,Mg)TiO3+ x +Bi2 O3 +Sb2 O5 MLCC with a high Ag content in the inner electrode of Ag/Pd=99/01. However, this was not the case with a low Ag content in the inner electrode of Ag/Pd=90/10. This means that the Bi,Sb-rich second phase plays an important role in determining the degradation of insulation resistance due to the excessive formation of oxygen vacancies from the reaction of Ag+ for Bi3+ or Sb5+ substitution to lower the activation energy of the (Zn,Mg)TiO3 +Bi2 O3 +Sb2 O5 dielectrics and to enhance markedly the effect of Ag migration. 相似文献
3.
In this study the phase relations between Pd or 70Ag/30Pd electrode systems with commercially important Bi-or Pb-based oxides were determined to establish the conditions under which detrimental interfacial chemical reactions may occur. For the reaction of Pd with Bi compounds, PdBi2 O4 formation was observed if the reaction proceeded at temperatures less than 835°C. At higher temperatures a Pd (Bi) alloy formed containing the maximum solubility of the Bi, i.e., 16 at.%. For the reaction of Pd with Pb compounds, a Pd (Pb) alloy formed which in all instances exhibited the maximum solubility of the Pb, i.e., 14 at.%. These reactions had an adverse effect on the local stoichiometry and composition of the dielectric, causing depletion of Bi or Pb. Studies on commercial capacitor dielectrics from DuPont (X7R and Z5U formulations) and Pb (Mg1/3 Nb2/3 )O3 showed that the use of Pd electrodes decreased the dielectric constant substantially, which was due to the formation of a low permittivity phase in series connectivity with the unaltered dielectric. 相似文献
4.
The Bi2 O3 -PbO phase diagram was determined using differential thermal analysis and both room- and high-temperature X-ray powder diffraction. The phase diagram contains a single eutectic at 73 mol% PbO and 635°C. A body-centered cubic solid solution exists above ∼600°C within a composition range of 30 to 65 mol% PbO. The compounds α-Bi2 O3 , σ5-Bi2 O3 , and γ-PbO (litharge) have wide solubility ranges. Four compounds, 6Bi2 O3 ·PbO, 3Bi2 O3 ·2PbO, 4Bi2 O3 ,5PbO, and Bi2 O3 ·3PbO, are formed in this system and the previously unreported X-ray diffraction patterns of the latter three compounds are reported. Diffraction patterns for some of these mixed oxides have been observed in ZnO-based varistors grown using Bi2 O3 and PbO as sintering aids. 相似文献
5.
Subsolidus phase relations in the system iron oride-Al2 O2 -Cr2 O3 in air and at 1 atm. O2 pressure have been studied in the. temperature interval 1250° to 1500°C. At temperatures below 1318° C. only sesquioxides with hexagonal corundum structure are present as equilibrium phases. In the temperature interval 1318° to 1410°C. in air and 1318° to 1495° C. at 1 atm. O2 , pressure the monoclinic phase Fe2 O3 . Al2 O3 with some Cr2 O3 in solid solution is present in the phase assemblage of certain mixtures. At temperatures above 1380°C. in air and above 1445°C. at 1 atm. O2 pressure a complex spinel solid solution is one of the phases present in appropriate composition areas of the system. X-ray data relating d- spacing to composition of solid solution phases are given. 相似文献
6.
Phase stability, sinterability, and microwave dielectric properties of Bi2 W2 O9 ceramics and their cofireability with Ag, Cu, and Au electrodes have been investigated. Single-phase Bi2 W2 O9 powder was synthesized by solid-state reaction in air at 800°C for 3 days. X-ray powder diffraction data show Bi2 W2 O9 to have an orthorhombic crystal structure described by the noncentrosymmetric space group Pna 21 , with lattice parameters a =5.4401(8), b =5.4191(8), c =23.713(4) Å. Ceramics fired at temperatures up to 865°C remain single-phase but above this temperature ferroelectric Bi2 WO6 appears as a secondary phase. The measured relative permittivity of Bi2 W2 O9 ceramics increases continuously from 28.6 to 40.7 for compacts fired between 860° and 885°C. The bulk relative permittivity of Bi2 W2 O9 corrected for porosity was calculated as 41.3. Bi2 W2 O9 ceramics fired up to 875°C exhibit moderate quality factors, Q × f r , ∼7500–7700 GHz and negative temperature coefficient of resonant frequency, ∼−54 to −63 ppm/°C. Chemical compatibility experiments show Bi2 W2 O9 ceramics to react with both Ag and Cu electrodes, but to form good contacts with Au electrodes. 相似文献
7.
Structural Dependence on Sintering Temperature of Lead Zirconate-Titanate Solid Solutions 总被引:2,自引:0,他引:2
P. GR. LUCUTA FL. CONSTANTINESCU D. BARB 《Journal of the American Ceramic Society》1985,68(10):533-537
Pb(Zr0.525 Ti0.475 )O3 piezoceramics, both unmodified and doped with 2 wt% Bi2 O3 or Nb2 O5 , were prepared by the usual techniques, using sintering temperatures from 900° to 1250°C. The microstructural data showed that the sintering temperature which produces minimum porosity is altered by the oxide additions. X-ray diffraction demonstrated the coexistence of both ferroelectric phases. The lattice parameter measurements showed that the tetragonal and rhombohedra1 unit cells of the two ferroelectric phases depend on the sintering temperature. 相似文献
8.
From literature values of the thermodynamic activity of Pd in Ag/Pd solid solutions and the Gibbs free energy of formation of PdO as a function of temperature, subsolidus equilibrium phase relations in the Pd–Ag–O2 system have been calculated and compared to results from high-temperature XRD analyses. The developed model takes into account the nonideal activity of Pd in Ag/Pd solid solutions and confirms that increasing the Ag/Pd ratio or decreasing the oxygen activity decreases the temperature at which PdO reduces. It also accurately predicts that the temperature range over which the PdO reduces is broad for Ag-rich compositions, and narrow for Pd-rich compositions. 相似文献
9.
E. C. SUBBARAO 《Journal of the American Ceramic Society》1961,44(2):92-95
Subsolidus phase relations in the binary system PbO-Ta2 O5 were investigated by the quenching method. The following compounds were identified by X-ray diffraction patterns: PbO -2Ta2O5 , PbO Ta2 O6 , 3PbO 2Ta2 P5 , 2PbO Ta2 O6 , 5PbO -2Ta2 O5 , and 3PbOTa2 O5 The 1:1 compound has rhombohedral symmetry when it is prepared below 1150°C. Above this temperature, it yields an orthorhombic phase. Compounds with the same ratio of lead oxide to pentoxide exist in the systems PbO-Ta2 O6 and PbO-Nb2 O5 . 相似文献
10.
Grain-oriented Bi0.5 (Na0.85 K0.15 )0.5 TiO3 -Pb(Zr1− x Ti x )O3 (BNKT-PZT) ceramics were prepared via the reactive templated grain growth method, using platelike Bi4 Ti3 O12 particles. Factors that determine the degree of orientation were examined. Prereacted PZT gave a larger degree of orientation than PZT raw materials (PbO, ZrO2 , and TiO2 ) in the 75BNKT-25PZT ( x = 0.5) system. Increases in the titanium concentration in the PZT of the 75BNKT-25PZT system and in the BNKT concentration in the y BNKT-(100 − y )PZT ( x = 0.5) system increased the degree of orientation. The direction of material transport between BNKT and PZT was important to obtain ceramics with a large degree of orientation. 相似文献
11.
The microstructure of strontium titanate internal boundary layer capacitors at various stages in their processing was studied by transmission electron microscopy of rapidly quenched and normally cooled samples. Compositions containing excess TiO2 , Al2 O3 , and SiO2 have a completely wetting liquid phase at the sintering temperature; during cooling Tin O2 n −1 , Magneli phases precipitate at multiple grain junctions. Diffused metal oxides and flux (Bi2 O3 , PbO, CuO, and B2 O3 ) rapidly penetrate as a liquid phase along boundaries in postsintering heat treatment. This liquid phase disappears during slow cooling. 相似文献
12.
Phase relations in the system Bi2 O3 -WO3 were studied from 500° to 1100°C. Four intermediate phases, 7Bi2 O3 · WO3 , 7Bi2 O3 · 2WO3 , Bi2 O3 · WO3 , and Bi2 O3 · 2WO3 , were found. The 7B2 O · WO3 phase is tetragonal with a 0 = 5.52 Å and c 0 = 17.39 Å and transforms to the fcc structure at 784°C; 7Bi2 O3 · 2WO3 has the fcc structure and forms an extensive range of solid solutions in the system. Both Bi2 O3 · WO3 and Bi2 O3 · 2WO3 are orthorhombic with (in Å) a 0 = 5.45, b 0 =5.46, c 0 = 16.42 and a 0 = 5.42, b 0 = 5.41, c 0 = 23.7, respectively. Two eutectic points and one peritectic exist in the system at, respectively, 905°± 3°C and 64 mol% WO3 , 907°± 3°C and 70 mol% WO3 , and 965°± 5°C and 10 mol% WO3 . 相似文献
13.
Tsuyoshi Honma Yasuhiko Benino Takumi Fujiwara Takayuki Komatsu Ryuji Sato 《Journal of the American Ceramic Society》2005,88(4):989-992
The glass formation region, crystalline phases, second harmonic (SH) generation, and Nd:yttrium aluminum garnet (YAG) laser-induced crystallization in the Sm2 O3 –Bi2 O3 –B2 O3 system were clarified. The crystalline phases of Bi4 B2 O9 , Bi3 B5 O12 , BiBO3 , Sm x Bi1− x BO3 , and SmB3 O6 were formed through the usual crystallization in an electric furnace. The crystallized glasses consisting of BiBO3 and Sm x Bi1− x BO3 showed SH generations. The formation of the nonlinear optical BiB3 O6 phase was not confirmed. The formation (writing) region of crystal lines consisting of Sm x Bi1− x BO3 by YAG laser irradiation was determined, in which Sm2 O3 contents were∼10 mol%. The present study demonstrates that Sm2 O3 –Bi2 O3 –B2 O3 glasses are promising materials for optical functional applications. 相似文献
14.
Hyuk-Joon Youn Tomohiro Sogabe Clive A. Randall Tom R. Shrout Michael T. Lanagan 《Journal of the American Ceramic Society》2001,84(11):2557-2562
Dielectric properties and phase formation of Bi-based pyrochlore ceramics were evaluated for the Bi2 O3 –ZnO–Ta2 O5 system. The compositional range r Bi2 (Zn1/3 Ta2/3 )2 O7 · (1− r )(Bi3/2 Zn1/2 )(Zn1/2 Ta3/2 )O7 (0 ≤ r ≤ 1) in Bi2 O3 –ZnO–Ta2 O5 was investigated to determine the relative solubility of BZT cubic (α-BZT, r = 0) and the pseudo-orthorhombic (β-BZT, r = 1) end members. It was found that extrinsic factors, such as kinetically limited phase formation and bismuth loss, contribute to apparent phase boundaries in addition to thermodynamic stability of each phase. Considering this, the locations of true phase boundaries were r < 0.30 and r ≥ 0.74 for α and β phases, respectively. Dielectric constants between 58 and 80 and low dielectric loss (tan δ < 0.003) were measured for the complete compositional range. The temperature coefficient of capacitance was controlled by composition, which was found to be <30 ppm/°C at the edge of β-phase solid solution. In addition to the excellent dielectric properties these materials can be sintered at low temperatures, which make Bi-based pyrochlores promising candidates for high-frequency electronic applications. 相似文献
15.
Takeshi Takamori 《Journal of the American Ceramic Society》1990,73(1):158-160
The Bi2 O3 -rich side of the system Bi2 O3 -SiO2 was studied with powder X-ray diffraction and differential thermal analysis. In the composition 6Bi2 O3 . x SiO2 , the metastable γ phase (bcc) was observed to exist over the range of 0 < x ≤ 1. In most of the compositions studied, metastable phases of water-quenched melts transformed into another metastable phase before reaching stable phases. A modification of the phase diagram is proposed. 相似文献
16.
R. L. SHULTZ 《Journal of the American Ceramic Society》1973,56(1):33-36
The role of titanium oxide in some important refractory systems was elucidated by studying selected equilibria in the system CaO-MgO-iron oxide-titanium oxide at O2 pressures of 0.21 atm (air) and 10−9 atm and under the extreme reducing conditions imposed by the presence of metallic Ti in contact with the oxide phases. Solidus relations were determined for the system CaO-MgO-TiO2 in air; 6 composition triangles were delineated, within each of which 3 crystalline phases coexist in equilibrium with liquid at a constant solidus temperature. The solidus temperatures range from 1407° to 1670°C. There is also a composition area within which MgO coexists with a Ca4 Ti3 O10 -Ca3 Ti2 O7 solid solution, with solidus temperatures varying continuously from 1659° to 1670°C. Studies of reactions between MgO and titanium oxide in contact with metallic Ti in a closed system indicate that the mutual solubility between MgO and TiO at 1400°C is very small. Addition of 5 wt% TiO2 to the system CaO-MgO-iron oxide at 1500°C in air and in 10−9 atm O2 decreases the amount of iron oxide which can be absorbed by a CaO-MgO body without formation of a liquid phase; hence, titanium oxide has a strong deleterious effect on the refractoriness of such bodies. 相似文献
17.
Reaction pathways in the synthesis of three photorefractive silicates—γ-Bi12 SiO20 (BSO), γ-Bi12 GeO20 (BGO), and gamma-Bi12 TiO20 (BTO)—were systematically investigated. The main results were as follows: (i) all the reactions of the form 6Bi2 O3 + MO2 →> γ-Bi12 MO20 (SR1 for M = Si, SR2 for M = Ge, SR3 for M = Ti) in the solid state seemed to be diffusion-controlled processes and were affected by both temperature and time, where the reaction temperature increases in the order SR1 < SR2 < SR3; (ii) the metastable phases Bi2 SiO5 (tetragonal) in reaction SR1, Bi2 GeO5 (orthorhombic) in reaction SR2, Bi4 Ti3 O12 (orthorhombic) in reaction SR3 may be formed and seemed to greatly accelerate the above-mentioned solid-state reaction processes; and (iii) for a continuous heating process, pure γ-Bi12 SiO20 and γ-Bi12 GeO20 could be produced before melting, whereas pure γ-Bi12 TiO2 0 could not be produced, even if all the mixed phases had melted. 相似文献
18.
Anu Bajaj Atul Khanna Narendra K. Kulkarni Suresh K. Aggarwal 《Journal of the American Ceramic Society》2009,92(5):1036-1041
Bismuth borate glasses from the system: 40Bi2 O3 –59B2 O3 –1Tv2 O3 (where Tv=Al, Y, Nd, Sm, and Eu) and three glasses of composition: 40Bi2 O3 –60B2 O3 , 37.5Bi2 O3 –62.5B2 O3 and 38Bi2 O3 –60B2 O3 –2Al2 O3 were prepared by melt quenching and characterized by density, UV-visible absorption spectroscopy and differential thermal analysis (DTA) studies. Bismuth borate glasses exhibit a very strong optical absorption band just below their absorption edge. Glasses were devitrified by heat treatment at temperatures above their glass transition temperatures and the crystalline phases produced in them were characterized by Fourier transform infrared (FTIR) absorption spectroscopy and X-ray diffraction (XRD). Bi3 B5 O12 was found to be the most abundant phase in all devitrified samples. DTA studies on glasses and FTIR and XRD analysis on crystallized samples revealed that very small amounts of trivalent ion doping causes significant changes in the devitrification properties of bismuth borate glasses; rare-earth ions promote the formation of metastable BiBO3 –I and BiBO3 –II phases during glass crystallization. 相似文献
19.
Solid-state reactions of equimolar mixtures of Bi2 O3 and Fe2 O3 from 625° to 830°C and their kinetics were investigated. The reaction rates were determined from the integrated X-ray diffraction intensities of the strongest peaks of the reactants and products. The activation energy for the formation of BiFeO3 was 96.6±9.0 kcal/mol; that for a second-phase compound, Bi2 Fe4 O9 , which formed above 675°C, was 99.4±9.0 kcal/mol. Specific rate constants for these simultaneous reactions were obtained. The preparation of single-phase BiFeO3 from the stoichiometric mixture of Bi2 O3 and Fe2 O3 is discussed. 相似文献
20.
Jin-Seong Kim Ngoc-Huan Nguyen Myung-Eun Song Jong-Bong Lim Dong-Soo Paik Sahn Nahm Jong-Hoo Paik Byung-Hyun Choi Soon-Jae Yu 《International Journal of Applied Ceramic Technology》2009,6(5):581-586
Bi2 O3 was added to a nominal composition of Zn1.8 SiO3.8 (ZS) ceramics to decrease their sintering temperature. When the Bi2 O3 content was <8.0 mol%, a porous microstructure with Bi4 (SiO4 )3 and SiO2 second phases was developed in the specimen sintered at 885°C. However, when the Bi2 O3 content exceeded 8.0 mol%, a liquid phase, which formed during sintering at temperatures below 900°C, assisted the densification of the ZS ceramics. Good microwave dielectric properties of Q × f =12,600 GHz, ɛr =7.6, and τf =−22 ppm/°C were obtained from the specimen with 8.0 mol% Bi2 O3 sintered at 885°C for 2 h. 相似文献