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1.
The effects of SiO2 and Cr2O3 on the formation process of ZnO varistors were investigated. Prior to formation of the Zn2.33Sb0.67O4 spinel phase (Sp-phase), a spinel-like phase forms. However, this phase does not control the varistor microstructure. The Sp-phase and the Bi2O3-phase which were formed by the decomposition of the Bi2(Zn4/3Sb2/3)O6 pyrochlore phase played important parts in the control of the varistor microstructure. That is, the Bi2O3 phase produced in the reaction promotes the initial sintering of the varistor and the Sp-phase inhibits the ZnO grain growth. In this reaction, SiO2 and Cr2O3 play a role in decreasing the decomposition temperature of the pyrochlore phase. Decreasing the decomposition temperature below 900° C (where ZnO grain growth begins) leads to the inhibition of ZnO grain growth. 相似文献
2.
E. R. Leite M. A. L. Nobre E. Longo J. A. Varela 《Journal of Materials Science》1996,31(20):5391-5398
The microstructural evolution, grain growth and densification for the varistor systems ZnO-Bi2O3 (ZB), ZnO-Bi2O3-Sb2O3 (ZBS), ZnO-Bi2O3-Sb2O3-MnO-Cr2O3-CoO (ZBSCCM) were studied using constant heating rate sintering, scanning electron microscopy (SEM) andin situ phase formation measurement by high temperature X-ray diffraction (HT-XRD). The results showed that the densifying process is controlled by the formation and decomposition of the Zn2Bi3Sb3O14 pyrochlore (PY) phase for the ZBS and ZBSCCM systems. The addition of transition metals (ZBSCCM system) alters the formation and decomposition reaction temperatures of the pyrochlore phase and the morphology of the Zn7Sb2O12 spinel phase. Thus, the spinel grains act as inclusions and decrease the ZnO grain growth rate. Spinel grain growth kinetics in the ZBSCCM system showed ann value of 2.6, and SEM and HT-XRD results indicate two grain growth mechanisms based on coalescence and Ostwald ripening. 相似文献
3.
The degree of phase formation was investigated by Sb2O3 behaviour in the calcination process, and the change of microstructure and breakdown properties due to the phases formation in ZnO varistor. The samples were calcined at several temperatures for 2 h and were sintered at 1150 to 1300 ° C, respectively, for 1 h. After that,V-I characteristics were investigated. Phase analysis by X-ray diffraction and microstructures observation by SEM were done. As a result, spinel phase was not formed and low nonlinear resistance was shown in the samples without Sb2O3. In the samples containing Sb2O3, it was shown that the pyrochlore and spinel phase are formed at the conventional calcination temperature or even below that temperature. This primary spinel phase and the spinel phase transformed from pyrochlore phase in sintering process inhibit ZnO grain growth, and so nonlinear resistances should be changed. Hence ZnO grain growth in ZnO-based varistor system is strongly dependent on the Sb2O3 behaviour in the calcination process. 相似文献
4.
Effect of chromium on the phase evolution and microstructure of ZnO doped with bismuth and antimony 总被引:2,自引:0,他引:2
Crystalline phase formation and microstructure of ZnO varistors with a basic composition ZnO–Bi2O3–Sb2O3 were examined. Addition of chromium oxide to this basic varistor resulted in an α-spinel (α-Zn7Sb2O12) phase dissolving a significant amount of Cr, while the β-spinel did not. β-spinel transformed to pyrochlore during cooling,
whereas α-spinel hardly transformed to pyrochlore irrespective of the cooling conditions. When Sb2O3 was completely replaced by Cr2O3, ZnCr2O4 was formed instead of spinel. α-spinel particles were 1–2 μm in size and intra- as well as intergranular. ZnCr2O4 particles, smaller than 1 μm in size, however, were present as aggregates in the bismuth-rich matrix phase at the grain boundaries.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
5.
Yanqiu Huang Meidong Liu Yike Zeng Churong Li 《Journal of Materials Science: Materials in Electronics》2004,15(8):549-553
The ZnO-based ceramic films doped with Bi2O3, Sb2O3, MnO, Co2O3 and Cr2O3 were prepared for use as film varistors by a sol–gel method. The formation and the changes of the phases in the films doped with different dopants and annealed at different temperatures were investigated via X-ray diffraction analysis. Three secondary phases, i.e., Bi2O3, Zn7Sb2O12 spinel and ZnCr2O4, were detected in the films when the annealing temperature was above 550 °C. The lattice constants of ZnO and Zn7Sb2O12 spinel phase changed with dopants and the annealing temperature, indicating that the diffusion of the ions into the crystals of ZnO and spinel phase had taken placed. The redistribution of the ions changed the constituents of the intergranular phases and the relevant defect species in ZnO grains, and affected intensively the electrical properties of the films, which were used as film varistors. The highest nonlinear coefficient () with the lowest leakage current was achieved when the film, which was doped with Bi2O3, Sb2O3, MnO and Cr2O3, was annealed at 750 °C. 相似文献
6.
Investigations were made of varistor microstructure, the morphology of Bi2O3 at multiple ZnO grain junctions, Bi2O3/ZnO grain boundaries and ZnO/ZnO grain boundaries (especially whether Bi2O3 is present or not at the ZnO/ZnO grain boundary) by means of high-resolution transmission electron microscopy and X-ray microanalysis in the scanning transmission electron microscope. Bi2O3 at multiple ZnO grain junctions consists of small particles of 0.1m in diameter, and they are vitrified to some extent. It is suggested that bismuth ions dissolve into ZnO grains over a 30 nm range from a Bi2O3/ZnO grain boundary; however, there is no bismuth at ZnO/ZnO grain boundaries. 相似文献
7.
Baoshuai Huang Yunfei Liu Yinong Lu Hong Gao Hu Chen 《Journal of Materials Science: Materials in Electronics》2013,24(8):2785-2789
New pyrochlore ceramics Bi(1.5?x)Nd x MgNb1.5O7 with x = 0–0.6 were synthesized by doping Nd into the A site in the Bi1.5MgNb1.5O7 pyrochlore. The Nd substituted Bi1.5MgNb1.5O7 ceramics were prepared utilizing solid-state reaction and investigated by X-ray diffraction, scanning electron microscope and dielectric measurements. The crystal structure was characterized as single cubic pyrochlore phase for x ≤ 0.5 while the second phase appeared at x = 0.6. With increasing Nd content from 0 to 0.5, the lattice parameters decreased slightly and the average grain size pronouncedly reduced from ~7.5 to ~5.0 μm. The Nd incorporation resulted in attractive enhancement of the dielectric properties including the temperature coefficient of dielectric constant that was remarkably optimized with the lowest value of ?16 ppm/°C at x = 0.5. A good combination of low dielectric loss, superior temperature coefficient and high dielectric permittivity can be achieved for the composition of x = 0.5, which seems to be very appealing for the practical use in high-frequency multilayer ceramic capacitors. 相似文献
8.
《Materials Research Bulletin》2003,38(11-12):1601-1605
A simple co-precipitation technique had been successfully applied for the preparation of pure ultrafine single phase SrBi2Ta2O9. Ammonium hydroxide was used to precipitate Sr2+, Bi3+ and Ta5+ cations simultaneously. No pyrochlore phase was found while heating powder at 800 °C and pure SrBi2Ta2O9 phase was found to be formed by X-ray diffraction. Particle size and morphology was studied by scanning electron spectroscopy. Ferroelectric hysteresis loop parameters of these samples were also studied. 相似文献
9.
Composite materials have been synthesized by mixing 90% (or 95%) YBa2Cu3O7 and 10% (or 5%) Bi2Sr2Ca1Cu2O8 by weight, and firing at 900°C to promote grain growth by inducing a liquid phase (Bi2Sr2Ca1Cu2O8) in the system. The influence of the amount of liquid phase on the X-ray diffraction data and electrical properties is reported. Energy dispersive X-ray (EDX) analyses are also reported. The YBiBa2O6 phase is formed during the heat treatment and introduces additional chemical heterogeneities at the grain boundaries. A previously reported 2212-related superconducting phase, Bi2(Sr,Ba)2(Ca,Y)Cu2O8+y, could also be formed during the synthesis process, and its effect on the electrical resistance versus temperature measurements is discussed. Attempts to substitute RE ions (Dy3+, Er3+, Ho3+) for Y3+ in YBiBa2O6 have been successful and are reported in an appendix section. X-ray diffraction data are also reported. EDX analyses have been performed specifically for a typical ErBiBa2O6 compound and reveal the presence of a new Er2Ba4O7 phase. 相似文献
10.
Yeh-Wu Lao Shu-Ting Kuo Wei-Hsing Tuan 《Journal of Materials Science: Materials in Electronics》2009,20(3):234-241
The effects of powder bed on the microstructure and electrical properties of Bi2O3- and Sb2O3-doped ZnO specimens are investigated in the present study. By using a sufficient amount of powder bed, the weight loss of
Bi2O3 reduces from >95 to <20%. The reduction of weight loss enhances significantly the densification and grain growth of ZnO.
Furthermore, the use of powder bed can also reduce the size distribution of ZnO grains. Nevertheless, the presence of Bi2O3 residue results in the formation of a pyrochlore phase (Zn2Bi3Sb3O14) during the cooling down stage; its presence is detrimental to the nonlinear characteristics of ZnO–Bi2O3–Sb2O3 system. 相似文献
11.
The reaction mechanism of PbMg1/3Nb2/3O3-PbZrO3-PbTiO3 (PMN-PZT) perovskite phase prepared by the columbite route has been studied in the temperature range from 600 to 800 °C. The effects of heating and cooling rate during the calcination of 3PbO +MgNb2O6+PZT powder mixtures have also been investigated. Nearly pure perovskite phase, 0.9 PMN-0.1 PZTsolid solution with no pyrochlore phase, as determined by X-ray diffraction, could be prepared at 800 °C for 2 H. From DTA/TGA, dilatometry and XRD data the reaction mechanism of PMN-PZT solid solution formation could be divided into three steps: (i) decomposition of columbite (MgNb2O6) by reacting with PbO at 350 to 600 °C (ii) the formation of a B-site-deficient pyrochlore phase Pb2Nb1.33Mg0.17O5.50 at close to 650 °C, and (iii) the formation of perovskite phase PMN-PZT solid solution from the reaction of Pb2Nb1.33Mg0.17O5.50 pyrochlore phase with MgO and PZT above 650 °C. 相似文献
12.
The effect of Bi2O3 on microstructure, electrical properties, dielectric characteristics, and aging behavior vanadium oxide-doped zinc oxide varistor ceramics was systematically investigated. Analysis of the phase indicated that the ceramics modified with Bi2O3 consisted of ZnO grain as a main phase and a few secondary phases such as Zn3(VO4)2, ZnV2O4, BiVO4, V2O5, and Mn-rich phase. The average grain size increased from 5.6 to 7.2 μm and the sintered density decreased in the range of 5.51–5.37 g/cm3 up to 0.05 mol%, whereas a further addition increased it to 5.40 g/cm3 at 0.25 mol%. The breakdown field decreased from 4,874 to 2,205 V/cm with an increase in the amount of Bi2O3. The ceramics added with 0.025 mol% Bi2O3 were characterized by a surprisingly high nonlinear coefficient (60) and very low leakage current density (20 μA/cm2). Bi atoms in the bulk acted as a donor to increase the electron concentration with an increase in the amount of Bi2O3. 相似文献
13.
P. Prabhakar Rao K. Ravindran Nair P. Divya Peter Koshy V. K. Vaidyan 《Journal of Materials Science: Materials in Electronics》2005,16(10):663-666
Improved dielectric properties are observed in pyrochlore type oxides, Ca3Sm3−x BixTi7Nb2O26.5 (x = 1.0, 2.0 or 3.0) by Bi substitution. The dielectric constant increased with increasing Bi concentration. The dielectric
constant obtained for Ca3Bi3Ti7Nb2O26.5 is 110, whereas, without Bi (Ca3Sm3Ti7Nb2O26.5) it is 62 at 100 kHz. The Powder X-ray diffraction analysis reveals that cubic pyrochlore type phase is formed for all the
compositions. The experimental results further show that the formation of Bi substituted compounds is complete at a lower
temperature than the compounds without Bi. Microstructure studies reveal that the grains formed are acicular when Bi is present
in large amounts compared to cuboid grains in samples having no Bi. 相似文献
14.
A simple co-precipitation technique has been successfully applied for the preparation of pure single phase CaBi4Ti4O15 (CBT) powders. Ammonium oxalate and ammonium hydroxide were used to precipitate Ca2+, Bi3+ and Ti4+ cations simultaneously. No pyrochlore phase was found while heating powder at 600 C and pure CBT phase was found to be formed by X-ray diffraction. Particle size and morphology was studied by transmission electron microscopy (TEM). The room temperature dielectric constant at 1 kHz is 400. The ferroelectric hysteresis loop parameters of these samples were also studied. 相似文献
15.
《Materials Letters》2004,58(27-28):3474-3476
A simple coprecipitation technique had been successfully applied for the preparation of pure ultrafine single-phase CaBi2Ta2O9 (CBT). Ammonium hydroxide and ammonium oxalate were used to precipitate Ca2+, Bi3+ and Ta5+ cations simultaneously. No pyrochlore phase was found while heating powder at 800 °C and pure CaBi2Ta2O9 phase was found to be formed by XRD. Particle size and morphology was studied by transmission electron microscopy (TEM). The room temperature dielectric constant at 1 kHz is 100. The ferroelectric hysteresis loop parameters of these samples were also studied. 相似文献
16.
Elżbieta Jartych Agata Lisinska-Czekaj Dariusz Oleszak Dionizy Czekaj 《Materials Science-Poland》2013,31(2):211-220
The aim of this work was to prepare BiFeO3 by modified solid-state sintering and mechanical activation processes and to investigate the structure and hyperfine interactions of the material. X-ray diffraction and Mössbauer spectroscopy were applied as complementary methods. In the case of sintering, BiFeO3 phase was obtained from the mixture of precursors with 3 and 5 % excess of Bi2O3 during heating at 1023 K. Small amounts of impurities such as Bi2Fe4O9 and sillenite were recognized. In the case of mechanical activation, the milling of stoichiometric amounts of Bi2O3 and Fe2O3 followed by isothermal annealing at 973 K resulted in formation of the mixture of BiFeO3, Bi2Fe4O9, sillenite and hematite. After separate milling of individual Bi2O3 and Fe2O3 powders, mixing, further milling and thermal processing, the amount of desired BiFeO3 pure phase was significantly increased (from 70 to 90 %, as roughly estimated). From Mössbauer spectra, the hyperfine interaction parameters of the desired BiFeO3 compound, paramagnetic impurities of Bi2Fe4O9 and sillenite were determined. The main conclusion is that the lowest amount of impurities was obtained for BiFeO3 with 3 % excess of Bi2O3, which was sintered at 1023 K. However, in the case of mechanical activation, the pure phase formed at a temperature by 50 K lower as compared to solid-state sintering temperature. X-ray diffraction and Mössbauer spectroscopy revealed that for both sintered and mechanically activated BiFeO3 compounds, thermal treatment at elevated temperature led to a partial eliminating of the paramagnetic impurities. 相似文献
17.
D. G. Sousa G. D. Saraiva J. M. S. Filho J. M. Filho A. S. B. Sombra 《Journal of Materials Science: Materials in Electronics》2014,25(10):4450-4457
In this paper the ceramic matrix of TiFeNbO6 (TFNO) was studied. The TFNO phase was calcined at 1,075 °C and used to prepare the samples, of 2, 4, 6, 8 and 10 wt% of the Bi2O3 and sintered at 1,125 °C. These samples were characterized by X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy and dielectric microwave properties. XRD and RS were used to characterize these samples. The samples presented two new phases. The first phase is the tetragonal rutile structure with a space group of P42/mnm, equivalent at parent rutile Ti0.4Fe0.3 Nb0.3O2 (TFNO) with 040725 ICSD code, and the secondary phase belonging to the pyrochlore system Bi1.721Fe1.056Nb1.134O7 (BFNO), with a space group of Fd-3mZ (227), in a cubic structure. The dielectric properties have shown significant variation for 10 % Bi2O3-added sample, because the formation of the new phase (BFNO) contributes with the reduction of τ f from 281.12 to 77.45 ppm/°C and with increase in ε r , from 47.23 to 63.77 and an increase in the dielectric loss (tan δ), from 0.0016 to 0.0068, respectively. Even though, Bi2O3 additive deteriorates the dielectric loss of the ceramics, the permittivity has enhanced significantly, which is advantageous for reduction of the air gap between the probe and the DRA antennas that influences on the samples for future application in microwave. 相似文献
18.
JailL Jeong Young Ho Han Byeong Cheol Moon 《Journal of Materials Science: Materials in Electronics》2004,15(5):303-306
Effects of Bi2O3 addition on the microstructural development and magnetic properties of NiCuZn ferrites were studied. For low temperature sintering (<900 °C), 0.1–1.0 wt % of Bi2O3 was added to the NiCuZn ferrites. The grain size and bulk density gradually increased with the increase in the Bi2O3 content. Above 0.5 wt % Bi2O3, abnormal grain growth was observed. The specimen with 0.25 wt % Bi2O3 showed the highest initial permeability with good quality factors and a uniform microstructure. However, the specimen with greater than 0.5 wt % Bi2O3 demonstrated abnormal grain growth with lower initial permeabilities and poor quality factors. 相似文献
19.
The Bi1.5MgNb1.5O7 (BMN) thin films were prepared on platinum coated sapphire by rf magnetron sputter deposition. Effects of substrate temperature, sputter pressure and O2/(O2 + Ar) mixing ratio on phase structures and dielectric properties of thin films were investigated. The results indicated that sufficiently high substrate temperature and low sputter pressure would facilitate the formation of cubic pyrochlore in BMN thin films. Meanwhile, the appropriate O2/(O2 + Ar) mixing ratio of sputter atmosphere was required. The deposited Bi1.5MgNb1.5O7 cubic pyrochlore thin films with (222) oriented texture exhibited large tunability of ~ 50% at a maximum applied bias field of 1.5 MV/cm, with low dielectric loss of ~ 0.007. The temperature and frequency dependent dielectric measurements indicated that no noticeable dielectric dispersion was detected in BMN cubic pyrochlore thin films. 相似文献
20.
Systematic studies have been made of the grain growth and density of sintered ZnO-based systems containing one or more additive oxides of the type Nb2O5, Bi2O3, Sb2O3, CoO, Cr2O3, MnO2, NiO and Al2O3. These samples were characterized using such techniques as scanning electron microscopy, X-ray diffraction and electron probe microanalysis. The influence of the nature and amount of additive oxides and sintering temperature is discussed in relation to microstructure, density and the phases present. 相似文献