共查询到20条相似文献,搜索用时 15 毫秒
1.
Byoung-Ki Lee Yang-Il Jung Suk-Joong L. Kang Janusz Nowotny 《Journal of the American Ceramic Society》2003,86(1):155-160
Two series of experiments were performed to study the experimental conditions for the formation of {111} twins and related microstructures in barium strontium titanate ((Ba, Sr)TiO3 ). In the first series, the phase equilibria in the BaTiO3 –SrTiO3 –TiO2 system were determined. XRD and WDS analysis, done in the BaTiO3 -rich region, of 45(Ba,Sr)TiO3 –10TiO2 samples annealed at 1250°C for 200 h in air showed that (Ba,Sr)TiO3 was in equilibrium with Ba6 Ti17 O40 (B6 T17 ) and Ba4 Ti13 O30 phases with strontium solubility (Sr/(Ba + Sr)) of ∼0.02 and 0.20, respectively. In the second series the microstructures of samples consisting of a mixture of (Ba,Sr)TiO3 and 2.0 mol% TiO2 , were observed after sintering at 1250°C for 100 h in air. {111} twins formed only in the samples with faceted B6 T17 second phase particles, similar to the case of BaTiO3 . In these samples, abnormal grain growth occurred in the presence of the {111} twins. In contrast, no {111} twins formed and no abnormal grain growth occurred in the samples containing second phase particles other than B6 T17 . With an increased substitution of strontium for barium, the aspect ratio of abnormal grains containing {111} twin lamellae was reduced. This result was attributed to a reduction in the relative stability of the {111} planes with the strontium substitution. 相似文献
2.
Byoung-Ki Lee Sung-Yoon Chung Suk-Joong L. Kang 《Journal of the American Ceramic Society》2000,83(11):2858-2860
The experimental conditions for {111} twin formation in BaTiO3 were investigated. When BaTiO3 compacts without excess TiO2 were sintered either in an oxidizing atmosphere (air) or in a reducing atmosphere (95N2 –5H2 ), no {111} twins formed within the BaTiO3 grains and no abnormal grain growth occurred. In contrast, many {111} twins were present within the abnormally grown grains in the excess-TiO2 -containing BaTiO3 samples sintered in air, while no twins were observed in the excess-TiO2 -containing samples sintered in 95N2 –5H2 . X-ray diffraction analysis showed that excess TiO2 forms a Ba6 Ti17 O40 phase during sintering with the space group A 2/ a in air and a Ba6 Ti17 O40− x phase with the space group C in 95N2 –5H2 . It appears therefore that excess TiO2 and an oxidizing atmosphere are necessary for {111} twin formation in BaTiO3 . These results may also indicate that the interface structure between BaTiO3 and Ba6 Ti17 O40 influences the twin formation. 相似文献
3.
Miha Drofenik Darko Makovec Igor Zajc Hans T. Langhammer 《Journal of the American Ceramic Society》2002,85(3):653-660
Grain growth and semiconductivity of donor-doped BaTiO3 ceramics with an excess of BaO and additions of SiO2 or B2 O3 were studied. The microstructures and electrical measurements on sintered samples revealed that their electrical properties are related to the microstructure development of the sintered samples. Samples heated with an excess of BaO developed a normal microstructure during sintering, as a consequence of normal grain growth (NGG), and were yellow and insulating. In contrast, samples with an excess of BaO and an addition of SiO2 or B2 O3 exhibited anomalous grain growth (AGG) and were dark blue and semiconducting after sintering. When some BaTiO3 seed grains were embedded in a sample of donor-doped BaTiO3 with an excess of BaO (without SiO2 or B2 O3 ), AGG was observed, i.e., some seed grains grew into large grains and were blue and semiconducting. An explanation is given for why AGG is responsible for the oxygen release and the formation of semiconducting grains in donor-doped BaTiO3 and not NGG. 相似文献
4.
Myung-Goo Kang Doh-Yeon Kim Ho-Yong Lee Nong M. Hwang 《Journal of the American Ceramic Society》2000,83(12):3202-3204
The coarsening behavior of large seed particles during the sintering of BaTiO3 ceramics has been investigated. At 1350°C, the grains are faceted, and the seed particles grow extensively. At 1380°C, however, the grains are spherical, and coarsening of the seed particles is limited. The observed difference is discussed in terms of the growth mechanism and the atomic structure of the interfaces. 相似文献
5.
Silver and its alloys frequently are used as electrode material for BaTiO3 -based dielectrics. In the present study, a small amount of fine silver particles have been intimately mixed with BaTiO3 powder. The sintering and grain-growth behavior of the silver-doped BaTiO3 in air are investigated. The solubility of silver in BaTiO3 , as revealed by lattice-parameter measurement, electrical measurement, and electron probe microanalysis, is <300 ppm. The densification of BaTiO3 is slowed slightly by the addition of silver inclusions. However, the presence of a small amount (<0.3 wt%) of silver increases the amount and size of abnormal grains. When the silver content is >0.3 wt%, the grain growth of BaTiO3 then is prohibited by the silver inclusions. 相似文献
6.
Paul W. Rehrig Gary L. Messing Susan Trolier-McKinstry 《Journal of the American Ceramic Society》2000,83(11):2654-2660
BaTiO3 single crystals were grown via templated grain growth (TGG), which is a process in which a single-crystal "template" is placed in contact with a sintered polycrystalline matrix and then heated to migrate the single-crystal boundary into the matrix. Millimeter-sized, stoichiometric single crystals of BaTiO3 were produced by heating polycrystalline matrix with a relative density of 97% and a Ba/Ti ratio of <1.00, which was bonded to a BaTiO3 single crystal, at temperatures above the eutectic temperature. Growth rates of 590–790, 180–350, and 42–59 μm/h were observed for {111}-, {100}-, and {110}-oriented single-crystal templates, respectively. Lower-surface-energy facets were formed for {111}- and {100}-oriented templates, whereas {110} crystals maintained a {110} growth front, which indicated that this plane orientation was the lowest-energy surface in this system. SrTiO3 also was shown to be a suitable substrate for TGG of BaTiO3 . 相似文献
7.
Seok-Hyun Yoon Je-Hun Lee Doh-Yeon Kim Nong M. Hwang 《Journal of the American Ceramic Society》2002,85(12):3111-3113
Heavily doped barium titanate (BaTiO3 ) powders, one with a donor-rich and the other with an acceptor-rich composition, were prepared. After sintering, the donor-rich specimen exhibited a fine-grained microstructure but significant grain growth occurred in the acceptor-rich specimen. A stable dielectric behavior was observed only in the donor-rich fine-grained specimen over the temperature range studied. However, in both specimens, an undoped core region several hundred nanometers in size was detected. The core-shell structure appeared to be maintained in BaTiO3 under the conventional sintering conditions. 相似文献
8.
Yang-Il Jung Si-Young Choi Suk-Joong L. Kang 《Journal of the American Ceramic Society》2003,86(12):2228-2230
To study the effect of oxygen partial pressure on grain growth in BaTiO3 , TiO2 -excess samples have been sintered in air with and without a prior H2 heat treatment. Without prior H2 treatment, abnormal grain growth occurs below and above the eutectic temperature ( T e ). An introduction of H2 treatment before air sintering, however, increases the average grain size and suppresses the formation of abnormal grains during subsequent air sintering below and above T e . This H2 treatment effect has been explained in terms of a decrease of the driving force for the growth of faceted grains below a critical value for formation of abnormal grains. The observed grain-growth behavior under various atmospheres demonstrates the possibility of having various microstructures via control of oxygen partial pressure and initial grain size. 相似文献
9.
Hong-Ri Jin Seok-Hyun Yoon Jong-Heun Lee Je-Hun Lee Nong M. Hwang Doh-Yeon Kim Joo-Hwan Han 《Journal of the American Ceramic Society》2004,87(9):1747-1752
The effect of an external electric field on the grain-growth behavior of acceptor Mg-doped, undoped, and donor Nb-doped BaTiO3 ceramics was investigated. The acceptor-doped and undoped specimens showed enhanced grain growth at the positive-biased region. On the other hand, for the highly donor-doped specimens, grain growth was enhanced in the negative-biased region. The results have been explained in terms of defect polarization and the consequent change in the boundary potential. It has been suggested that liquid penetration into grain boundaries is critically dependent on the boundary potential. 相似文献
10.
11.
Grain-Boundary Chemistry of Barium Titanate and Strontium Titanate: I, High-Temperature Equilibrium Space Charge 总被引:2,自引:0,他引:2
Direct observations using scanning transmission electron microscopy (STEM) of the grain-boundary chemistry of selectively doped SrTiO3 and BaTiO3 show the predominant solute segregation in both systems to be that of acceptors (negative effective charge). Appreciable donor segregation is not observed even at lattice concentrations as high as 10 mol%. Donor and acceptor codoped materials show segregation of the acceptor only. The results are consistent with a grain-boundary space-charge distribution consisting of a positive boundary and negative space charge. All grain boundaries examined also show an excess of Ti relative to the A-site cations, suggesting that the positive boundary charge is at least partially accommodated by an excess of Ti ions. The sign and magnitude of the electrostatic potential appear to be remarkably insensitive to changes in lattice defect structure with solute doping. Grain-boundary chemistry appears dominated by space-charge segregation, in contrast with the predictions of recent atomistic simulations which neglect the space-charge potential. 相似文献
12.
Miha Drofenik 《Journal of the American Ceramic Society》1990,73(6):1587-1592
The grain growth of donor-doped BaTiO3 prepared from BaTiO3 powders with different initial specific surface areas was studied. Results show that a higher initial surface area and, consequently, a smaller critical grain size at the phase boundary drastically increase the critical amount of donor dopant, causing the grain size anomaly during sintering. 相似文献
13.
Effect of Green States on Sintering Behavior and Microstructural Evolution of High-Purity Barium Titanate 总被引:1,自引:0,他引:1
Compacts prepared from three differently agglomerated powders were studied. Hg-penetration results and SEM observations were employed to compare the uniformity of powder compacts and to investigate the pore-size evolution and the microstructural development during sintering. It was found that the more nonuniform the powder compact, the higher the degree of pore growth in the initial and at the beginning of intermediate stages of sintering. Moreover, a higher sintering temperature and a nonuniform microstructure with larger grains could not be avoided. Microstresses might develop because of the differential shrinkage, but they would be released thereafter via the change of grain morphology. It was observed that the aggregate and pore-boundary separation might not be the primary reason for the initiation of discontinuous grain growth. 相似文献
14.
15.
Small amounts of niobium (donor) doping in barium titanate (BaTiO3 ) cause semiconductivity in this material. When the amount of niobium is increased slightly, the BaTiO3 is converted back to an insulator. This phenomenon is attributed to donor segregation. Such an insulating material can recover its semiconductivity when specific amounts of acceptors are introduced. The space-charge segregation theory explains that such acceptors can prevent the segregation of donors. Impedance/modulus analysis of BaTiO3 with a slightly increased niobium content and with no or a minimal amount of magnesium (acceptor) show a response of a third resistance–capacitance (RC) network, in addition to the two that have been thought to be caused by the grains and grain boundaries. The response of the third RC network is not observed at greater magnesium concentrations that give a recovery of the semiconductivity. This study suggests that acceptors can inhibit the donor segregation. 相似文献
16.
Myung-Koo Kang Young-Sung Yoo Doh-Yeon Kim Nong M. Hwang 《Journal of the American Ceramic Society》2000,83(2):385-390
Two different types of BaTiO3 seed particles, normal and twinned seeds of ∼30 μm on the average, were prepared from crushed sintered specimens. Normal seeds were obtained from the usual BaTiO3 sintered compacts, while twinned seeds containing a double twin were obtained from BaTiO3 compacts sintered with 2 mol% of SiO2 . The BaTiO3 powder compacts were again prepared with 5 wt% of seed grains and sintered under various conditions. The microstructural evolution was quite different in the two cases: the growth of normal seed grains was ultimately limited but that of the twinned seeds continued extensively. The observed difference is discussed in terms of the growth mechanism and the atomic structure of interfaces. 相似文献
17.
When properly doped, barium titanate ceramics display positive temperature coefficient resistance (PTCR) behavior. This has been proved to be a Schottky barrier type of grain-boundary effect. However there has not yet been a complete point-to-point comparison between the experimental data and theory for the entire set of the material nonlinear dielectric properties. In this study, a methodology has been developed which allows the study of the depletion layer dielectric properties while the PTCR effect is being investigated. An equivalent dielectric constant, the value of which is to be determined from this experiment, is treated as an average of the dielectric properties of the depletion layer and is used to analyze the grain-boundary resistance and capacitance data based on a simple double-depletion-layer model. The theoretical relationship between this equivalent dielectric constant and the material dielectric properties is also explored in this study. 相似文献
18.
The effects of excess free barium ions in aqueous barium titanate slip on the resulting BaTiO3 tape properties were investigated in terms of the slip behavior, green/sintered tape density and morphology, and dielectric properties. The excess free barium ions expressed by means of the Ba/Ti ratio adversely affected most tape properties. Increase in the slip viscosity, green porosity, and agglomeration along with a decrease in mechanical properties and green/sintered density were found with the increase in the Ba/Ti ratio. However, dielectric permittivity was increased with increase in the Ba/Ti ratio. An effort was made to correlate these phenomena with Ba2+ leaching in water for realistic multilayer ceramic capacitor applications. 相似文献
19.
It has been discovered that the formation of the butterfly twin in barium titanate depends on both the average particle size and the particle-size distribution of the starting material. Maximum twin yields occur when the particles have an average size near 1μ with a rather sharp cutoff in the distribution in the large-particle region. All impurities act to decrease twin yield, principally because they interfere with stacking-fault formation which also is necessary for twinning to occur. 相似文献
20.
When BaTiO3 ceramics were sintered at relatively low temperatures (≤1250°C), the grains with reentrant edges caused by a (111) double twin grew exclusively. As a result, a microstructure with a bimodal grain-size distribution composed of platelike large grains and fine matrix grains was obtained. In contrast, at the usual sintering temperature between 1250° and 1350°C, grains containing a (111) double twin did not exhibit any growth advantage. In this case, a coarse and uniform microstructure was obtained. When this coarse-grained specimen was further heat-treated at 1365°C, the grains possessing a double twin were observed to grow exclusively again. The results were explained in terms of a coarsening process controlled by two-dimensional nucleation. 相似文献