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1.
K. Park J.-G. Kim W.-S. Cho 《Journal of Materials Science: Materials in Electronics》2002,13(1):13-19
Rutile TiO2 (a=4.594 å and c=2.958 å) phase was formed on the outer region of Ti powders after oxidation at 600 °C for 1–300 h. Porous (Ba,Sr)TiO3 ceramics were fabricated by adding partially oxidized Ti powders (4–8 vol %) into (Ba,Sr)TiO3 powders, and showed excellent positive temperature coefficient of resistivity (PTCR) characteristics after paste-baking treatment at 580 °C in air. The PTCR characteristics of the porous ceramics were mainly attributed to the adsorption of oxygen at the grain boundaries. The microstructure and electrical properties of the porous (Ba,Sr)TiO3 ceramics containing the partially oxidized Ti powders oxidized at 600 °C for different oxidation times (1–300 h) were investigated. 相似文献
2.
Porous n-BaTiO3 ceramics are synthesized by the addition of pore-forming agent into the (Ba,Sr)TiO3 powder. From the DTA-TGA analysis for samples containing the PEG and corn-starch, it was found that an exotherm occurred at 262 and 315°C, respectively, weight loss commenced at 165 and 252°C, and was virtually complete by 265 and 472°C, respectively. The porosity of n-BaTiO3 ceramics increased and the grain size decreased with increasing the pore-forming agent. From the XRD analysis at high angles, all the samples with and without the pore-forming agent at room-temperature exhibit the tetragonal structure. PTCR jump of the samples containing pore-forming agent is 1-2 orders higher than that of sample without the pore-forming agent. It is also found that the development of PTCR characteristic in the porous n-BaTiO3 ceramics containing pore-forming agent is related to grain boundaries, which basically equals that in ordinary BaTiO3 without pore-forming agent, from the complex impedance results. 相似文献
3.
J.-G. Kim W.-P. Tai J.-M. Lee J.-G. Ha S.-M. Lim 《Journal of Materials Science: Materials in Electronics》2004,15(4):241-245
We fabricated porous (Ba,Sr)(Ti,Sb)O3 ceramics by adding potato-starch (1–20 wt %) and investigated the effects of sintering temperature (1300–1450 °C) and time (0.5–10 h) on the positive temperature coefficient of resistivity characteristics of the porous ceramics. The room-temperature electrical resistivity of the (Ba,Sr)(Ti,Sb)O3 ceramics decreased with increasing sintering temperature, while that of the ceramics increased with increasing sintering time. For example, the room-temperature electrical resistivity of the (Ba,Sr)(Ti,Sb)O3 ceramics for the samples sintered at 1300 °C and 1450 °C for 1 h is 6.8×103 and 5.7×102 cm, respectively, while that of the ceramics is 6.5×102 and 1.3×107 cm, respectively, for the samples sintered at 1350 °C for 0.5 h and 10 h. In order to investigate the reason for the decrease and increase of room-temperature electrical resistivity of the samples with increasing sintering temperature and time, the average grain size, porosity, donor concentration of grains (N
d), and electrical barrier height of grain boundaries () of the samples are discussed. 相似文献
4.
A. G. Belous O. I. V'yunov L. L. Kovalenko V. Buscaglia M. Viviani P. Nanni 《Inorganic Materials》2003,39(2):133-138
An approach is proposed for fabricating fine-grained, low-resistivity BaTiO3-based PTCR ceramics via partial isovalent substitutions on the Ba site. The grain size of the ceramics thus prepared is shown to decrease as the ratio of ionic radii r(Ba2+)/r(M2+) (M = Ca, Sr, Pb) increases. Isovalent substitutions on the Ba site narrow down the range of donor dopant (yttrium) concentrations in which PTCR materials can be prepared. The experimental results agree well with thermodynamic calculations under the assumption that the materials contain the Y3+Ti3+O3 phase, as suggested by ESR data, which point to the presence of Y3+–Ti3+ associates. Partial calcium, strontium, and lead substitutions on the Ba site reduce the average grain size of PTCR ceramics, which is probably due to the lattice strain arising from the isovalent substitution. Partial replacement of Ba2+ with mixtures of different isovalent elements (e.g., Sr2+ and Pb2+) offers the possibility of obtaining fine-grained, low-resistivity PTCR ceramics, without changing the phase transition temperature. 相似文献
5.
PTCR characteristics of semiconducting barium titanate ceramics produced by high-energy ball-milling
K. Park J.-G. Ha C.-W. Kim Jun-Gyu Kim 《Journal of Materials Science: Materials in Electronics》2008,19(4):357-362
We studied the influence of potato-starch content and ball-milling time on the positive temperature coefficient of resistance
(PTCR) characteristics of porous and semiconducting barium titanate ceramics, which were produced by high-energy ball-milling
followed by solid state reaction. The sintered samples at room temperature crystallized in the tetragonal structure, irrespective
of the potato-starch content and ball-milling time. As the ball-milling time increased, the porosity and pore size of the
samples decreased, while and the grain size increased. Higher potato-starch content yielded a smaller grain size and higher
porosity. The potato-starch additive and ball-milling time had little influence on the donor concentration of the grains.
A larger PTCR jump was obtained with the addition of potato-starch mainly as a consequence of an increase in the porosity.
A higher ball-milling time yielded both lower electrical resistivity and a lower PTCR jump. 相似文献
6.
《Materials Letters》2006,60(25-26):3027-3030
Perovskite barium–strontium titanate, (Ba,Sr)TiO3 was prepared and effects of Sb2O3 additives on its PTCR properties were investigated. The (Ba,Sr)TiO3 with 0.05∼0.25 mol% Sb2O3 showed semiconducting PTCR behavior and anomalous grain growth was also observed when sintered at 1360 °C. It was considered that charge compensation by doping Sb2O3 as well as anomalous grain growth by sintering leads to resistivity reduction from insulating to semiconducting transition. 相似文献
7.
J.-G. Kim J.-H. Sim W.-S. Cho 《Journal of Materials Science: Materials in Electronics》2003,14(2):109-113
Porous Ba(Ti,Sb)O3 ceramics were fabricated by adding corn-starch at 20 wt %. The effect of atmosphere on the PTCR characteristics of the porous Ba(Ti,Sb)O3 ceramics and the role of oxygen on the grain boundaries in the PTCR characteristics of the Ba(Ti,Sb)O3 ceramics were investigated. In air, O2, N2, and H2 atmospheres, the electrical resistivity of Ba(Ti,Sb)O3 ceramics below 150 °C was independent of atmosphere, while it was strongly dependent on atmosphere above 200 °C. The low electrical resistivity in reducing atmospheres was due to a decrease in potential barrier height, which originated from an increase in the number of electrons owing to the desorption of chemisorbed oxygen atoms at the grain boundaries. In a N2 atmosphere, the electrical resistivity of Ba(Ti,Sb)O3 ceramics during the cooling cycle was lower than that during the heating cycle, and then the electrical resistivity of the porous Ba(Ti,Sb)O3 ceramics during subsequent heating and cooling cycles was increased again by exposure to an O2 atmosphere. 相似文献
8.
Z. Z. Huang S. U. Adikary H. L. W. Chan 《Journal of Materials Science: Materials in Electronics》2002,13(10):605-608
The processing behavior of PTCR ceramics of (Ba,Sr,Ca,Pb)TiO3 solid solution composition with additives of lanthanum oxide (La2O3) and boron nitride (BN) was studied. The ceramics can be sintered at temperatures as low as 1100 °C and possess rather low room-temperature resistivity with good PTCR effect. The sample ball milled with de-ionized water exhibits a more uniform microstructure compared to the sample ball-milled with alcohol. Particle size of less than 1 m was found to be adequate for preparing the ceramics and the finer particles (0.45 m) do not significantly improve the PTCR behavior. The performance of the PTCR sample is not sensitive to the sintering parameters such as the sintering time and cooling rate. This may be ascribed to the presence of excess BaO in the sample and the low sintering temperature, thereby eliminating the effect of Ba ion vacancies on the properties of the PTCR sample. 相似文献
9.
The electrical properties and microstructure of (Ba,Y)TiO3 PTCR ceramics were studied. The results indicate that the Mn ions increase the intergranular barrier height and produce a high-resistance layer on the grain surface. The temperature-dependent resistances of the grain bulk, surface layer, and grain boundaries, the temperature coefficient of resistance, and the magnitude of the varistor effect were assessed as a function of Mn content. 相似文献
10.
Zhi Cheng Li Lena Smuk Bill Bergman 《Journal of Materials Science: Materials in Electronics》2004,15(8):561-567
(Ba0.69Pb0.31)TiO3 ceramics were prepared using Al2O3, SiO2, additives and excess of TiO2 (AST). The characteristics of positive temperature coefficient of resistivity (PTCR) was studied and the corresponding microstructures were investigated using atomic force microscopy and scanning electron microscopy. The results showed that the PTCR effect was related to the AST additives. The maximum value of resistivity in the ceramics with lower content of or without Al2O3 and SiO2 additives was much lower than in those with AST additives. Ceramics with low AST content, which were heated by electric field to a temperature much higher than their Curie temperature, lost the PTCR effect after the electric field stimulation. The microstructure observations revealed that re-crystallization took place in the ceramics with lower content of or without AST additives resulting in the loss of the PTCR effect. 相似文献
11.
J.-G. Kim W.-P. Tai Y.-J. Kwon K.-J. Lee W.-S. Cho N.-H. Cho C.M. Whang Y.-C. Yoo 《Journal of Materials Science: Materials in Electronics》2004,15(12):807-811
Donor doped BaTiO3 (n-BaTiO3) ceramics were fabricated by adding polyethylene glycol (PEG) at 20 wt %. The effects of reducing and oxidizing atmospheres on the PTCR characteristics of the porous n-BaTiO3 ceramics were investigated. The PTCR characteristics of the porous n-BaTiO3 ceramics is strongly affected by chemisorbed oxygen at the grain boundaries and are recovered as the atmosphere is changed from the reducing gas to oxidizing gas. The low room-temperature resistivity of the porous n-BaTiO3 ceramics in reducing atmospheres may be caused by the decrease in potential barrier height, which originates from an increase in the number of electrons owing to the desorption of chemisorbed oxygen atoms at the grain boundaries. In addition, the high room-temperature resistivity of the porous n-BaTiO3 ceramics in oxidizing atmospheres may be caused by the increase in potential barrier height, which results from the adsorption of chemisorbed oxygen atoms at the grain boundaries. 相似文献
12.
Preparation of Barium Strontium Titanate Ceramic by Sol-Gel Method and Microwave Sintering 总被引:1,自引:0,他引:1
Wen Yang Aimin Chang Bangchao Yang 《Journal of Materials Synthesis and Processing》2002,10(6):303-309
The (Ba,Sr)TiO3 amorphous gel was prepared by sol-gel process and calcined in the 2.45-GHz multimode microwave furnace to synthesize (Ba,Sr)TiO3 nanopowder. The calcination temperature of the (Ba,Sr)TiO3 ceramic powders that convert the material into prevoskite phase can be reduced from 1100°C to 900°C, the nanopowder displays the highest sinterability. Using a new kind of insulator materials made of MgAl2O4–LaCrO3, the crack-free and dense (Ba0.80Sr0.20)TiO3 ceramics with fine grain size (<1 µm) were prepared by microwave sintering at 1310°C for 15 min. The fine (Ba,Sr)TiO3 ceramics sintered by microwave sintering technique display lower dielectric loss than that of conventional samples, indicating a reduction of the influence of defects with the microwave process. 相似文献
13.
Ting Wu Yongping Pu Pan Gao Dan Liu 《Journal of Materials Science: Materials in Electronics》2013,24(10):4105-4112
Sr x Ba1?x TiO3 (x = 0.50–0.70) ceramics were prepared by conventional solid-state method. The effects of Sr/Ba ratio on the microstructures, energy storage properties and dielectric relaxation behaviors of ceramics were systematically investigated. Scanning electron microscopy observations revealed that the grain size was inhibited with increasing Sr molar fraction. The Sr0.6Ba0.4TiO3 ceramics obtained the highest energy density of 0.3629 J/cm3 attributed to the increase of average breakdown strength resulting from the decrease of grain size and the optimizing of microstructure. In order to investigate the influence of Sr/Ba ratio on the dielectric relaxation behaviors, the activation energy has been calculated from the relaxation of dielectric loss and the complex impedance spectra by the Arrhenius relationship, respectively. The same results indicated that the decrease of grain size resulting in more grain boundaries, it was difficult for transferring charge and making an orientation under external electric field. Meanwhile, more defects existed at grain boundary and accelerated the thermally activated motions of defects, leading to the increase of activation energy. 相似文献
14.
S. Jayanthi T. R. N. Kutty 《Journal of Materials Science: Materials in Electronics》2006,17(11):883-897
The influence of B2O3, and Al2O3 as segregative additives in modifying the ρ–T characteristics has been studied in BaTiO3 ceramics with positive temperature coefficient of resistance (PTCR). Reaction of Al2O3 at the grain boundary regions of BaTiO3 ceramics leads to the segregation of the secondary phase, BaAl6TiO12 resulting in broad PTCR jump, whereas B2O3 addition gives rise to steeper resistivity jump. Microstructure studies by SEM reveal the formation of coherent second phase
layer of barium aluminotitanate surrounding the BaTiO3 grains. The EDX results shows varying Al to Ti ratio in the early stage of phase formation in BaAl6TiO12 resulting in electrically active layer around the BaTiO3 grains. The TiO2-excess melt formation results in lower resistivity for 2–4% Al2O3 containing n-BaTiO3 ceramics whereas at higher alumina contents, BaAl6TiO12 phase becomes dominant leading to higher resistivity in the sample. Complex impedance analyses support the three-layer regions,
corresponding to the contributions from grain interior resistance (R
g), grain boundary resistance (R
gb), and that from secondary phase (R
sec). Electron paramagnetic resonance spectroscopy (EPR) indicated barium vacancies, V
Ba
/
as the major electron trap centers which are activated across the tetragonal-to-cubic phase transition. A charge trapping
mechanism is proposed wherein the segregation of secondary phases bring carrier redistribution among the various acceptor
states thereby affecting the electrical conductivity of n-BaTiO3 ceramics. The presence of Al3+–O−–Al3+ or Ti4+–O−–Al3+ type hole centers at the grain boundary layer (GBL) regions results in charge redistribution across the modified phase transition
temperature due to symmetry-related vibronic interactions resulting in broad PTCR characteristics extending to higher temperatures. 相似文献
15.
The effect of consolidation pressure and crystallite size of powders crystal phases of TiO2 on sintered microstructure of TiO2 ceramics doped with 0.25 mol % Nb and 1.0 mol % Ba were investigated. Also, the development sequence of abnormal grain growth
of (niobium, barium) doped TiO2 ceramics was proposed. The second phases of as-sintered surface were determined. The dielectric properties of Ag-electroded
samples were correlated with the resistivity of the bulk (Nb, Ba) doped TiO2 ceramics. Abnormal grain growth lowered the resistivity of bulk material of (Nb, Ba) doped TiO2 ceramics, and moved the relaxation frequency of fan δ to high frequency region over 105 Hz. Controlling the sintered microstructures can obtain reasonably good dielectric properties. 相似文献
16.
D. J WANG Z. L GUI L. T LI 《Journal of Materials Science: Materials in Electronics》1997,8(4):271-276
A typical positive temperature coefficient of resistance (PTCR) effect in yttrium-doped (Sr, Pb)TiO3 ceramics made by chemical processing was obtained for the first time. The results show that the room temperature resistivity
is lower than 102 Ω cm and the resistivity jump is above 106. The breakdown voltage is above 340 V mm−1 (a.c.). The sintering temperature is about 1100°C, lower than for conventional BaTiO3 ceramics.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
Formation, microstructure, and electrophysical properties of positive temperature coefficient of resistance ceramics of the systems (Ba0.996Y0.004)TiO3 and (Ba0.746Ca0.1Sr0.15Y0.004)TiO3 with manganese as acceptor dopant have been investigated. Is has been shown that manganese ions increase the potential barrier at grain boundaries and form a high-resistance outer layer in PTCR ceramics. The resistance of grains, outer layers and grain boundaries, and the value of the temperature coefficient of resistance as a function of the manganese content of positive temperature coefficient of resistance materials have been investigated. 相似文献
18.
Minghe Cao Dongxiang Zhou Shuping Gong Yunxiang Hu 《Journal of Materials Science: Materials in Electronics》2002,13(3):121-124
The influence of TiCl3 solution on the room temperature (r.t.) resistivity and electrical properties of Ba0.92Ca0.08TiO3 PTCR ceramics was studied. The results indicate that the PTC effect can be improved significantly when an appropriate amount of TiCl3 in solution is added to the original materials. Some of the doped Ti3+ ions segregate at grain boundaries behaving as acceptors by substituting for Ti site or valence varying (from Ti3+ to Ti4+). As a result, the surface charge density N
s) increases and the barrier height at grain boundaries () is enhanced. 相似文献
19.
Yongping Pu Haidong Wu Jifeng Wei Bo Wang 《Journal of Materials Science: Materials in Electronics》2011,22(9):1479-1482
As a positive temperature coefficient of resistivity (PTCR) material, Ba0.92Ca0.05(Bi0.5Na0.5)0.03TiO3 ceramics with donor doping of Nb5+ and acceptor doping of Mn2+ were prepared by a conventional mixed oxide method. The influence of contents of Nb5+ and Mn2+ on the microstructure and PTCR characteristics of Ba0.92Ca0.05(Bi0.5Na0.5)0.03TiO3 ceramics sintered at 1,360°C for 2 h was investigated. The result showed that the Curie temperature (T
c) was shifted to a lower temperature with increasing of the content of Nb5+ and the resistance jump (ρmax/ρmin) was enhanced with doping of Mn2+. The grain size of ceramic sample decreased with increasing of contents of donor Nb5+ and acceptor Mn2+. The Ba0.92Ca0.05(Bi0.5Na0.5)0.03TiO3 ceramic with 0.4 mol%Nb5+ and 0.04 mol%Mn2+ exhibited a low ρRT of 5.0 × 102 Ω cm, a typical PTCR effect of ρmax/ρmin > 103, and a T
c of 158°C. 相似文献
20.
N. Y. Chan S. H. Choy D. Y. Wang Y. Wang J. Y. Dai H. L. W. Chan 《Journal of Materials Science: Materials in Electronics》2014,25(6):2589-2594
(Ba1?x,Srx)(Zr0.1,Ti0.9)O3 (BSZT) ceramics with x = 0, 0.05, 0.15, 0.25, 0.35 and 0.45 were prepared by conventional solid state reaction method. The structural characterization with X-ray diffraction and scanning electron microscopy indicate a monotonical drop in lattice constants and grain size with the increase of Sr concentration. Consequently, the Curie temperature and remnant polarization of the ceramics exhibit a strong compositional dependence. A linear relationship between the Curie temperature and Sr concentration is revealed. At x = 0.45, the BSZT ceramics show substantially high tunability of over 55 % under 20 kV/cm dc electric field with very low dielectric loss value of 0.0025 at room temperature, suggesting the BSZT ceramics could be a promising alternative to traditional (Ba,Sr) TiO3 ferroelectrics for developing high frequency tunable dielectric devices. 相似文献