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1.
Feng Gao Li-Hong Cheng Rong-Zi Hong Jia-Ji Liu Yong-Hong Yao Chang-Sheng Tian 《Journal of Materials Science: Materials in Electronics》2008,19(12):1228-1232
Grain-oriented Na0.5Bi0.5TiO3-BaTiO3 (NBTBT) ceramics were fabricated by reactive-templated grain growth using plate-like Bi2.5Na3.5Nb5O18 (BNN) as templates. The specimens are composed of NBTBT perovskite phase and BNN lay-structured phase. Textured ceramics
have a brick-wall microstructure with strip-like grains aligning in the direction parallel to the casting plane and exhibit
an {h00} preferred orientation. The texture fraction increases initially, and then decreases with increasing sintering temperature.
The optimal sintering temperature is 1,185 °C where the texture fraction has a maximum value of 0.58 and d33 is 98 pC/N. The textured NBTBT ceramics show evidence of relaxor ferroelectrics with diffuse phase transition and frequency
dispersion because of composite biphasic structure. 相似文献
2.
A. V. Shlyakhtina A. V. Knot’ko L. L. Larina S. A. Borichev L. G. Shcherbakova 《Inorganic Materials》2004,40(12):1312-1316
The high-temperature (>1600°C) order—disorder phase transition of Tm2Ti2O7 is shown to be irreversible. The 740°C ionic conductivity of nanocrystalline Tm2Ti2O7 ceramics synthesized at 1670°C is 2 × 10-3 S/cm and remains unchanged upon heat treatment in air at 860°C for 240 h. The conductivity of the high-temperature (disordered pyrochlore) phase of Tm2Ti2O7 is independent of grain size in the range 20–30 nm.Translated from Neorganicheskie Materialy, Vol. 40, No. 12, 2004, pp. 1495–1500.Original Russian Text Copyright © 2004 by Shlyakhtina, Knotko, Larina, Borichev, Shcherbakova. 相似文献
3.
Xiuli Chen Huanfu Zhou Liang Fang Dongjin Chu Changda Li Ruili Guo Hong Wang 《Journal of Materials Science: Materials in Electronics》2011,22(4):371-375
The influences of B2O3 and CuO (BCu, B2O3: CuO = 1:1) additions on the sintering behavior and microwave dielectric properties of LiNb0.6Ti0.5O3 (LNT) ceramics were investigated. LNT ceramics were prepared with conventional solid-state method and sintered at temperatures
about 1,100 °C. The sintering temperature of LNT ceramics with BCu addition could be effectively reduced to 900 °C due to
the liquid phase effects resulting from the additives. The addition of BCu does not induce much degradation in the microwave
dielectric properties. Typically, the excellent microwave dielectric properties of εr = 66, Q × f = 6,210 GHz, and τ
f
= 25 ppm/oC were obtained for the 2 wt% BCu-doped sample sintered at 900 °C. Chemical compatibility of silver electrodes and low-fired
samples has also been investigated. 相似文献
4.
Hong-Tie Soong Cheng-Hsing Hsu Cheng-Liang Huang Ming-Ta Kuo 《Journal of Materials Science》2007,42(7):2393-2398
The microwave dielectric properties and the microstructures of Sm(Co1/2Ti1/2)O3 ceramics with B2O3 additions (0.25 and 0.5 wt%) prepared by conventional solid-state route have been investigated. The prepared Sm(Co1/2Ti1/2)O3 exhibited a mixture of Co and Ti showing 1:1 order in the B-site. Doping with B2O3 (up to 0.5 wt%) can effectively promote the densification of Sm(Co1/2Ti1/2)O3 ceramics with low sintering temperature. It is found that Sm(Co1/2Ti1/2)O3 ceramics can be sintered at 1,260 °C due to the grain boundary phase effect of B2O3 addition. At 1,290 °C, Sm(Co1/2Ti1/2)O3 ceramics with 0.5 wt% B2O3 addition possess a dielectric constant (ε
r) of 27.7, a Q × f value of 33,600 (at 9 GHz) and a temperature coefficient of resonant frequency (τf) of −11.4 ppm/ °C. The B2O3-doped Sm(Co1/2Ti1/2)O3 ceramics can find applications in microwave devices requiring low sintering temperature. 相似文献
5.
Polycrystalline samples of (Pb0.25Sr0.75)TiO3 (PST75) were prepared by the solid-state reaction method. The effects of firing temperatures and excess PbO on PST75 ceramics
were investigated. The PST75 was calcined between 600 and 1000 °C for 3 h and the sintering temperature ranged between 1050
and 1250 °C for 2 h. The optimized calcination and sintering conditions were identified as 950 and 1250 °C, respectively.
The lattice parameter c increased, while the lattice parameter a decreased with increased firing temperatures. The average particle size and average grain size increased with increased firing
temperatures. After the addition of PbO—excess 0, 1, 3, 5, and 10 wt%—in the PST75 samples, the lattice parameter a decreased. The average particle size and the average grain size increased with the increase of PbO. The porous microstructure
slightly decreased with an increasing amount of PbO—up to 3 wt%—then slightly increased with the higher excess PbO. The density
was improved by adding 3 wt% of excess PbO. A low dielectric loss was observed from the 3 wt% excess PbO sample. 相似文献
6.
Hiroshi Maiwa 《Journal of Materials Science》2008,43(19):6385-6390
Ba(Zr0.2Ti0.8)O3 (BZT) ceramics are prepared from spray-dried powder by spark plasma sintering (SPS) and by normal sintering. By the application
of SPS, ceramics with >96% relative densities could be obtained by sintering at 1,100 °C for 5 min in air atmosphere. The
pellet as sintered by SPS at 1,100 °C was black and conductive. Although SPS was carried out in air atmosphere, the samples
were deoxidized by heating the carbon die. By post-annealing at 1,000 °C for 12 h in air, the pellet was oxidized and became
white and insulating. Grain growth was suppressed in the ceramics prepared by SPS, and the average grain size was 0.52 μm.
The starting powder contained 1.90% carbon, mainly as binder, and the SPS-prepared ceramics and ordinary prepared ceramics
contained 0.15 and 0.024% carbon, respectively. The BZT ceramics obtained by SPS and the subsequent annealing at 1,000 °C
for 12 h exhibited a mild temperature dependence of their dielectric constant. The field-induced displacement of the BZT ceramics
was less hysteretic and smaller than that of the ceramics sintered by the conventional method. 相似文献
7.
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
8.
Fangli Yu Jianfeng Yang Yaohui Xue Jun Du Yuan Lu Jiqiang Gao 《Bulletin of Materials Science》2009,32(2):177-181
Porous Si3N4 ceramics were successfully synthesized using cheaper talc and clay as sintering additives by pressureless sintering technology
and the microstructure and mechanical properties of the ceramics were also investigated. The results indicated that the ceramics
consisted of elongated β-Si3N4 and small Si2N2O grains. Fibrous β-Si3N4 grains developed in the porous microstructure, and the grain morphology and size were affected by different sintering conditions.
Adding 20% talc and clay sintered at 1700°C for 2 h, the porous Si3N4 ceramics were obtained with excellent properties. The final mechanical properties of the Si3N4 ceramics were as follows: porosity, P
0 = 45·39%; density, ρ = 1·663·g·cm−3; flexural strength, σ
b (average) = 131·59 MPa; Weibull modulus, m = 16·20. 相似文献
9.
In some electroceramic materials, their unique electrical properties are due to potential barriers, i.e., double Schottky barriers (DSBs), formed at grain boundaries. So far, some researchers have revealed that the electrical properties of DSB are closely related to grain boundary characters, especially grain boundary coherency. For example, highly coherent boundary does not give PTCR or varistic property, while random types exhibit clear resistivity jump or abrupt current increment. Therefore, a concept of grain boundary design will be required for future device manufacturing, even in bulk materials. But it has not been clarified yet why the electron transport behaviors depend on them. In order to address this question, it is necessary to carry out a systematic experiment focusing on single grain boundaries using well-defined bicrystals.In the present study, we have summarized our studies with a special interest in electron transport behavior across single grain boundaries for n-type BaTiO3, SrTiO3 and ZnO. 相似文献
10.
Jie Su Xiaomei Lu Chao Zhang Junting Zhang Song Peng Xiaobo Wu Kangli Min Fengzhen Huang Jinsong Zhu 《Journal of Materials Science》2011,46(10):3488-3492
Ho3Fe5O12 ceramics were fabricated by the solid-state reaction method. The results revealed an increase of the grain size, dielectric
constant, and dielectric loss, while a decrease of the remnant magnetization and coercive field with increasing sintering
temperature. A dielectric relaxation behavior was observed, which might be associated with the charge carrier hopping between
Fe2+ and Fe3+. A cole–cole fitting to loss peaks revealed a dependence of the activation energy and the broaden factor on the relative density of the
samples. Furthermore, at appropriate frequencies, the 1250 °C-sintered samples showed high dielectric constant, low dispassion,
and good temperature stability around room temperature. 相似文献
11.
Jianfeng Zhu Guoquan Qi Haibo Yang Fen Wang 《Journal of Materials Science: Materials in Electronics》2011,22(1):96-100
The microstructure and electrical properties of ZnO-Bi2O3-based varistor ceramics doped by Pr6O11 in the content range of 0–5.49 wt% were investigated at different sintering temperatures (1,100, 1,150, 1,175, 1,200 °C).
The increase of sintering temperature leads to more dense ceramics, which increases the nonlinear property, whereas it decreases
the voltage-gradient and leakage current. With increasing Pr6O11 content, the breakdown voltage increases because of the decreases of ZnO grain size. The improvement of non linear coefficient
together with the decrease of leakage current are related to the uniformly distribution of secondary phases along the grain
boundaries of the ZnO. The varistors sintered at 1,175 °C with the 3.37 wt% Pr6O11 doping possess the best electrical properties: the varistor voltage, nonlinear coefficient, and leakage current are 340 V/mm,
46 and 0.63 μA, respectively. 相似文献
12.
The electrical properties of donor (La3+) doped BaTiO3 samples with a donor concentration in the range from 0.3 to 1.5 mol.% of La were studied. Samples were sintered at a low partial pressure of oxygen in order to facilitate anomalous grain growth and donor incorporation. In order to optimise the PTCR anomaly, the samples were annealed in air at 1100°C. Results show that with the use of a specific sintering profile PTCR ceramics containing an amount of donor dopant >0.3 mol.%, can be prepared. Heavily doped samples which do not exhibit anomalous grain growth show a core shell structure. 相似文献
13.
The M23C6 precipitation behavior in a cast Ni-base superalloy M963 was investigated after tensile creep testing at 800°C and strain-controlled low cycle fatigue testing at 700–950°C. During high temperature creep and low cycle fatigue, the primary MC decomposed into M6C continuously, and a great amount of secondary carbide, chromium-rich M23C6, precipitated preferentially in the periphery of MC and γ +γ′ eutectic at grain boundaries. M23C6 was rarely present in grain interior, indicating that grain boundary promoted M23C6 carbide precipitation. The M23C6 precipitation was closely dependent on the stress state and testing temperature, seemed to be independent of the total strain amplitude. M23C6 is unstable during low cycle fatigue testing. The occurrence of M23C6 precipitation was sharply reduced during low cycle fatigue testing at 950°C. Crack was easily initiated at interface between MC and matrix, while fine M23C6 was effective to prevent grain boundary migration. 相似文献
14.
We have studied the effect of hot-pressing conditions (different pressure rise rates and isothermal holding temperatures in the range 1450–1550°C) on the microstructure of ceramics produced from nanopowder with the composition Ce0.09Zr0.91O2/MgAl6O10/γ-Al2O3 (20.6, 37.4, and 42.0 wt %, respectively). Firing at 1450°C for 1 h made it possible to obtain fine-grained ceramics with less than 3 μm in grain size. The compaction pressure rise rate was shown to be a key parameter under such thermal conditions (20 + 10°C/min → 1450°C). Grain growth was prevented most effectively when the maximum load, 30 MPa, was reached at a temperature of 1000°C. Under such conditions, the grain size was 0.4–0.8 μm and the relative density reached 98.8%. 相似文献
15.
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
16.
Daojiang Gao K. W. Kwok Dunmin Lin H. L. W. Chan 《Journal of Materials Science》2009,44(10):2466-2470
CeO2-doped K0.5Na0.5NbO3 lead-free piezoelectric ceramics have been fabricated by a conventional ceramic fabrication technique. The ceramics retain
the orthorhombic perovskite structure at low doping levels (<1 mol.%). Our results also demonstrate that the Ce-doping can
suppress the grain growth, promote the densification, decrease the ferroelectric–paraelectric phase transition temperature
(T
C), and improve the dielectric and piezoelectric properties. For the ceramic doped with 0.75 mol.% CeO2, the dielectric and piezoelectric properties become optimum: piezoelectric coefficient d
33 = 130 pC/N, planar electromechanical coupling coefficient k
p = 0.38, relative permittivity εr = 820, and loss tangent tanδ = 3%. 相似文献
17.
Zi-de Yu Xiao-ming Chen Han-li Lian Qian Zhang Wen-xin Wu 《Journal of Materials Science: Materials in Electronics》2018,29(22):19043-19051
Pure K0.5Na0.5NbO3 lead-free piezoelectric ceramics without any dopants/additives were sintered at various temperatures (950–1125 °C) in low pO2 atmosphere (pO2?~?10?6 atm). All ceramics exhibit high relative densities (>?94%) and low weight loss (<?0.6%). Compared to the ceramics sintered in air, the ceramics sintered in low pO2 exhibit improved electrical properties. The piezoelectric constant d33 and converse piezoelectric constant d33* are 112 pC/N and 119 pm/V, respectively. The ceramics show typical ferroelectric behavior with the remnant polarization of 21.6 µC/cm2 and coercive field of 15.5 kV/cm under measurement electric field of 70 kV/cm. The good electrical properties of the present samples are related to the suppression of volatility of the alkali cations during the sintering process in low pO2 atmosphere. 相似文献
18.
Choon-W. Nahm 《Journal of Materials Science: Materials in Electronics》2011,22(8):1010-1015
The microstructure, electrical properties, and DC-accelerated aging behavior of the ZnO-V2O5-Mn3O4 ceramics were investigated at different sintering temperatures of 850–925°C. The microstructure of the ZnO-V2O5-Mn3O4 ceramics consisted of ZnO grain as a primary phase, and Zn3(VO4)2 which acts as a liquid-phase sintering aid, in addition to Mn-rich phase as secondary phases. The maximum value (3,172 V/cm)
and minimum value (977 V/cm) of breakdown field were obtained at sintering temperature of 850 and 900°C, respectively. The
nonlinear coefficient exhibited the highest value, reaching 30 at 925°C and the lowest value, reaching 4 at 850°C. The optimum
sintering temperature was 900°C, which exhibited not only high nonlinearity with 24 in nonlinear coefficient, but also the
high stability, with %ΔE1mA = −0.9% and %∆α = −12.5% for DC-accelerated aging stress of 0.85 E1mA/85°C/24 h. 相似文献
19.
Kyung-Han Seo Bong-Ho Lee Nam-Kyoung Kim Jaejung Ko 《Journal of Materials Science》2005,40(23):6151-6156
Stabilization tendencies of the perovskite structure in a Pb(Zn1/3Ta2/3)O3-BaTiO3 pseudobinary system with/without compositional modification by 20 mol% PbTiO3 introduction were compared. In order to promote perovskite phase formation, the B-site precursor method (which is conceptually
similar to the columbite process) was employed in this study. Dielectric properties of sintered samples were investigated
as functions of composition and measurement frequency. Dielectric constant spectra, in the paraelectric temperature region,
were further analyzed in terms of diffuseness. Microstructures of sintered specimens were also investigated and correlated
with perovskite stabilization. 相似文献
20.
V. I. Voronkova V. K. Yanovskii E. P. Kharitonova O. G. Rudnitskaya 《Inorganic Materials》2005,41(7):760-765
Bi2VxW1 − x
O6 − y
ceramics are synthesized, and their structure and electrical properties are studied. The results indicate that the Bi2WO6-Bi2VO5.5 system contains Bi2WO6- and Bi2VO5.5-based solid solutions in the ranges 0 < x ≤ 0.2 and 0.75 ≤ x < 1, respectively. Tungsten stabilizes the high-temperature, tetragonal phase γ-Bi2VO5.5, which persists down to room temperature at 0.75 ≤ x ≤ 0.84. In the range 350–550°C, the electrical conductivity of the bismuth-vanadate-based solid solutions exceeds that of Bi2VO5.5 by about one order of magnitude. The conductivity of the Bi2WO6-based solid solutions is also higher than that of the host phase.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 866–870.Original Russian Text Copyright © 2005 by Voronkova, Yanovskii, Kharitonova, Rudnitskaya. 相似文献