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1.
The efficiency of simultaneous application of chemically-derived starting powders and melt-forming sintering aids in low temperature
sintering has been demonstrated. Doping of cryochemically processed BiNbO4 powders with CuO/V2O5 causes reducing sintering temperatures from 850–900∘C to 700–720∘C. Similar doping of Zn3Nb2O8 fine powders allows to obtain ceramics with density 97–98% and Q × F values up to 40 000 GHz at T > 720∘C. The sintering of solution-derived BaCeO3 powders doped with CuO results in dense ceramics at T = 1000∘C. Morphological evolution during sintering was observed using hot stage SEM. Low temperature liquid phase sintering of fine
powders is rather sensitive to the traces of secondary phases and to the micromorphology of starting powders though observed
reduction of sintering temperatures is substantially larger than for traditional liquid phase sintering of coarse-grained
oxide powders. 相似文献
2.
ZnNb2O6-TiO2 mixture thin films with multilayer structures were fabricated via a sol-gel spin coating process. TiO2 layers were deposited on the pre-crystallized ZnNb2O6 layers in order to suppress the formation of the ixiolite phase which always forms in the bulk system. The phase constitution
of the thin films, confirmed by X-ray diffraction (XRD), could be controlled by the annealing temperatures, which, in turn,
influenced the dielectric properties of the thin films. TiO2 layers crystallized as the anatase phase and then transformed to the rutile phase at temperatures higher than 725∘C. Dielectric constants of the mixture thin films, measured at 1 MHz with an MIM (metal-insulator-metal) structure, increased
from 27 to 41 with dielectric losses below 0.005 as the annealing temperature increased from 700∘C to 900∘C. The increase in the dielectric constants was understood to originate from the increasing amounts of the rutile phase. Temperature
coefficients of capacitance (TCC) were also measured between 25∘C and 125∘C, which showed a decreasing manner from positive values to negative values with increasing annealing temperatures. When annealed
at 850∘C, the TCC of the thin films could be tuned to be approximately 0 ppm/oC with dielectric constant and dielectric loss of 36 and 0.002, respectively. 相似文献
3.
Jae Chun Lee Hyuk Chun Kwon Yong-Pil Kwon Sung Park Hae-Won Lee Jong-Ho Lee Joosun Kim 《Journal of Electroceramics》2006,17(2-4):1109-1111
Porous ceramic fiber composites were coated with pyrolytic carbon by the decomposition of either propane or infiltrated phenolic
resin in a nitrogen atmosphere at 800–900∘C. The amount of carbon coating was varied to tailor the electrical conductivity of the carbon-coated composites. The electrical
and thermal conductivity of the composites were measured at room temperature using a two-point method and a hot-wire one,
respectively. Up to 30 wt% pyrolytic carbon, the electrical conductivity σ showed linearly increasing tendency and was fitted
by the effective conductivity according to the parallel rule of a mixture σ =ΣV
i⋅σi with an effective conductivity of pyrolytic carbon σc and volume fraction of coated carbon V
c. The electrical conductivity of coated carbons prepared from propane at 900∘C and phenolic resin at 800∘C was of the order of 100 and 10−1 S cm−1, respectively. 相似文献
4.
Acceptor doped-ceria is a possible electrolyte material for the IT-SOFC (intermediate temperature solid oxide fuel cell) due
to its high oxygen-ion conductivity. However, its use has been limited by its mechanical weakness and the appearance of electronic
conductivity in reducing condition. In this study, alumina was selected as an additive in the doped-ceria to see if it increases
the oxygen-ion conductivity and mechanical strength. Effects of alumina addition in doped ceria were studied as a function
of alumina content and acceptor (Gd) content.
The electrical conductivity of (Ce1−x
Gd
x
O2−δ)1−y
+ (Al2O3)
y
(x = 0–0.35, y = 0–0.10) was measured by using impedance spectroscopy. The grain conductivity of Ce0.8Gd0.2O2-δ (GDC20) with 5 mol% alumina increased ∼3 times from that of GDC20 at 300∘C. The grain conductivity was even ∼2 times higher than that of Ce0.9Gd0.1O2−δ (GDC10) at 300∘C. The electrical conductivity of GDC20 without alumina addition, measured at 500∘C in air, rapidly decreased after exposure to reducing condition (Po2∼10−22 atm) at 800∘C. However, the decrease was much slower in GDC20 with alumina addition, indicating the improved mechanical strength.
Among the examined compositions, (Ce0.75Gd0.25 O2-δ)0.95 + (Al2O3)0.05 (GDC25A5) showed the highest conductivity at most temperatures. 相似文献
5.
LaNi0.6Co0.4O3 (LNC) is a perovskite-type conducting ceramic oxide, which is an ideal electrode layer for perovskite ferroelectric and piezoelectric
thin and thick film devices, owing to its unique crystal structure that can facilitate film growth and improve fatigue behavior.
When used for thick films, however, one of the drawbacks is its high sintering temperature of above 1200∘C, which can lead to severe inter-diffusion. In an attempt to reduce the sintering temperature of LNC without substantially
deteriorating the electrical properties, we have investigated the effects of doping LNC with an appropriate glass addition.
LNC powder was synthesized through a solid state reaction process. Varying amounts of glass compositions were then introduced,
in order to study their effects on densification, microstructure and electrical properties of LNC. The glass compositions
exhibited a strong effect on the sintering behaviors and microstructure, where the density after sintering was improved with
increasing amount of glass addition. While the electrical conductivity was adversely affected by an increasing amount of glass
addition, the composition with optimal glass addition showed a lowered sintering temperature of 950∘C, and at the same time maintained a high conductivity of 117 S cm−1. 相似文献
6.
Doped ceria (CeO2) compounds are fluorite type oxides, which show oxide ionic conductivity higher than yttria stabilized zirconia, in oxidizing
atmospheres. As a consequence of this, considerable interest has been shown in application of these materials for `low (500∘–650∘C)’ temperature operation of solid oxide fuel cells (SOFCs). In this study, some rare earth (eg. Gd, Sm, and Dy) doped CeO2 nano-powders were synthesized via a carbonate co-precipitation method. Fluorite-type solid solution were able to be formed
at low temperature, such as 400∘C and dense sintered bodies were subsequently fabricated in the temperature ranging from 1000∘ to 1450∘C by conventional sintering (CS) method. To develop high quality solid electrolytes, the microstructure at the atomic level
of these doped CeO2 solid electrolytes were examined using transmission electron microscopy (TEM). The specimens obtained by CS had continuous
and large micro-domains with a distorted pyrochlore structure or related structure, within each grain. We conclude that the
conducting properties in these doped CeO2 systems are strongly influenced by the micro-domain size in the grain. To minimize the micro-domain size, spark plasma sintering
(SPS) was examined. SPS has not been used to fabricate dense sintered bodies of doped CeO2 electrolytes, previously; carbon from the graphite dies penetrates the specimens and inhibits densification. To overcome
this challenge, and to be able to produce dense sintered bodies of doped CeO2 of a grain size that minimizes the microdomain growth, a combination of SPS and CS methods were examined. Using this combined
method we report that we were able to produce fully dense specimens with improved conductivity. This is correlated with a
reduction in the size of the micro-domains. Consequently we conclude that the control of micro-domain size within the grain
structure is a key component in the successful design of electrolyte materials with improved conductivity. 相似文献
7.
Ferroelectric Ba0.5Sr0.5TiO3 (BST) films were prepared on Pt/Ti/SiO2/Si substrates by the sol-gel process. The films were spin-coated at 2000 rpm for 30 secs and then pyrolysed for 5 mins at
the temperature of 350∘C. This coating procedure was repeated for 3, 4, 5 and 6 times to obtain BST films with different thicknesses. After coating
the films with the desired repetition times, the films were finally annealed in a conventional furnace at temperatures ranging
from 600∘C to 800∘C with a 50∘C interval in between. The films obtained with an annealing procedure of 750∘C were polycrystalline with the presence of an impurity BaCO3 phase. The capacitance and leakage current were measured and used to extract information on the metal-BST interface. With
the series capacitance model and modified Schottky emission equation, the thickness of the dead layers for Au/BST and Pt/BST
interfaces were calculated to be less than 6 nm and 5 nm, respectively. 相似文献
8.
Aurivillius-type structure compounds are good candidates for their use as high temperature piezoelectrics, due to their high
ferro-paraelectric phase transition temperature. However, this characteristic correlates with a high coercive field that makes
difficult the poling process, necessary to have piezoelectric activity. The electric properties, specially conductivity, limit
the maximum poling field. On the other hand, piezoelectric properties are directly related to the ferroelectric remanent polarization.
Thus, the study of both characteristics is towards improving the piezoelectric properties of these materials.
In this work, ceramics with nominal composition (SrBi2Nb2O9)0.35(Bi3TiNbO9)0.65 (TC∼ 760^∘C), prepared by hot pressing of mechanically activated precursors, have been studied. The electrical properties (permittivity,
dielectric loss factor and d.c. conductivity) as a function of frequency and temperature have been measured, up to temperatures
higher than the ferro-paraelectric phase transition, and their anisotropy explained in terms of the ceramic texture. Well-saturated
ferroelectric hysteresis loops at 250∘C have been obtained, with values of Pr = 21.4 μ C/cm2 and Ec = 70.4 kV/cm. 相似文献
9.
P-type thermoelectric Bi0.5Sb1.5Te3 compounds were prepared by the spark plasma sintering method with temperature ranges of 300–420∘C and powder sizes of ∼75 μm, 76–150 μm, 151–250 μm. As the sintering temperature increased, the electrical resistivity and
thermal conductivity of the compound were greatly changed due to an increase in the relative density. The Seebeck coefficient
and electrical resistivity were varied largely with decreasing the powder size. Subsequently, the compound sintered at 380∘C with the powders of ∼75 μm showed the maximum figure-of-merit of 2.65 × 10−3K−1 and the bending strength of 73 MPa. 相似文献
10.
ZnGa2O4 thin film phosphors have been synthesized on ITO coated glass and soda-lime glass at a firing temperature of 500∘C and an annealing temperature of 500∘C and 600∘C via a chemical solution method using Zinc acetate dihydrate, Gallium nitrate hydrate and 2-methoxiethanol as a solution.
XRD patterns of the film phosphors synthesized showed the peaks of ZnGa2O4 crystalline phases. AFM surface morphologies of the ZnGa2O4 thin film phosphors revealed marked differences according to an annealing temperature of 500∘C and 600∘C under an annealing atmosphere (3% H2/Ar). On the other hand, the sheet resistance of ZnGa2O4 thin film phosphors, which were measured by four-point probe instrument, was approximately 5.76 Ω /square and 7.86 Ω /square
with annealing temperature, respectively. The ZnGa2O4 thin film phosphors exhibited blue emission spectra with peak wavelength of 434 nm and 436 nm by ultra-violet excitation
around 230 nm. 相似文献
11.
Films of (1−x)Pb(Zn1/3Nb2/3)O3-xPb(Zr0.4Ti0.6) O3 (x = 0.6, 40PZN-60PZT) were deposited on Pt/TiO2/ SiO2/Si substrate through spin coating. Using a combination of homogeneous precursor solution preparation and two-step pyrolysis
process, we were able to obtain the 40PZN-60PZT thin films of perovskite phase virtually without pyrochlore phase precipitation
after annealing above 650∘C. But since annealing done at the high temperatures for extended time can cause diffusion of Pt, TiO2 and Si, and precipitation of nonstoichiometric PbO, we adopted 2-step annealing method to circumvent these problems. The
2-step annealed films show dense microstructure than the 1-step films annealed at higher temperature. Furthermore, the root-mean-square
surface roughness of 220 nm thick films which are annealed at 720∘C for 1 min and then annealed at 650∘C for 5 min was found to be 3.9 nm by atomic force microscopy as compared to the 12 nm surface roughness of the film annealed
only at 720∘C for 5 min. The electrical properties of 2-step annealed films are virtually same and those of the 1-step annealed films
annealed at high temperature. The film 2-step annealed at 720∘C for brief 1 min and with subsequent annealing at 650∘C for 5 min showed a saturated hysteresis loop at an applied voltage of 5 V with remanent polarization (P
r) and coercive voltage (V
c) of 25.3 μC/cm2 and 0.66 V respectively. The leakage current density was lower than 10−5A/cm2 at an applied voltage of 5 V. 相似文献
12.
I. H. Kim D. Y. Ku J. H. Ko D. Kim K. S. Lee J.-h. Jeong T. S. Lee B. Cheong Y.-J. Baik W. M. Kim 《Journal of Electroceramics》2006,17(2-4):241-245
To improve the stability of sputter-deposited ZnO:Al (AZO) films at high temperature above 300∘C, an amorphous Zn-Sn-O (ZTO) film was deposited on the top of AZO films as an protective layer by co-sputtering of pure ZnO
and SnO2 targets. Amorphous ZTO films had resistivity in the range from 10−2 to 10−3 Ωcm and were stable up to temperature of 400∘C. Heat treatments of bare AZO films in the atmosphere at 400∘C resulted in a dramatic increase in the resistivity accompanied by substantial decrease in carrier concentration and Hall
mobility. The AZO films covered with the ZTO film showed remarkable improvement in thermal stability for subsequent heat treatments
in the temperature range from 200 to 400∘C in the atmosphere as well as chemical stability in weak acidic solution. X-ray photoelectron spectroscopy analysis showed
that the improvement was attained by ZTO layer acting as diffusion barrier of oxygens and/or water vapors. 相似文献
13.
A systematic investigation of cerium and stannum doped 0.94(Bi0.5Na0.5)TiO3−0.06BaTiO3 (Sn&Ce-BNT6BT) based lead-free piezoelectric ceramics is undertaken to understand the influence of sintering temperature
on electrical properties. The X-ray diffraction patterns showed that all of the Sn&Ce-BNT6BT ceramics exhibited a single perovskite
structure with the co-existence of the rhombohedral and tetragonal phase. The smaller grain size of Sn&Ce-BNT6BT ceramics
was obtained at lower sintering temperature, and more cubical grains of Sn&Ce-BNT6BT ceramics were obtained at higher sintering
temperature. The temperature dependence of dielectric permittivity of the compositions exhibited strong dispersion with the
increasing temperature, and the dielectric loss tangent increased dramatically while the temperature over 225∘C. The depolarization temperature T
d
of Sn&Ce-BNT6BT ceramics sintered at 1160∘C was 92.6∘C. The remnant polarizations P
r
for Sn&Ce-BNT6BT ceramics sintered at 1120 and 1200∘C were found to be 28.8 and 33.4 μC/cm2 at room temperature, respectively. 相似文献
14.
Ceramics of 0.2CaTiO3-0.8Li0.5Nd0.5TiO3) have been prepared by the mixed oxide route using additions of Bi2O3-2TiO2 (up to 15 wt%). Powders were calcined 1100∘C; cylindrical specimens were fired at temperatures in the range 1250–1325∘C. Sintered products were typically 95% dense. The microstructures were dominated by angular grains 1–2 μm in size. With increasing
levels of Bi2O3-2TiO2 additions, needle and lath shaped second phases developed. For Bi2Ti2O7 additions up to 5 wt%, the relative permittivity increased from 95 to 131, the product of dielectric Q value and measurement frequency increased from 2150 to 2450 GHz and the temperature coefficient of resonant frequency (τ
f
) increased from −28pp/∘C to +22pp/∘C. A product with temperature stable τ
f
could be obtained at ∼2 wt% Bi2Ti2O7 additions. For high levels of additives, there is minimal change in relative permittivity, the Qxf values degrade and τ
f
becomes increasingly negative. 相似文献
15.
The amorphous films were annealed in a wide temperature range (250–1000∘C) and film properties of TiO2 thin films were studied. Nano-sized anatase polycrystallites had been induced by thermal annealing for the films annealed
at and above 300∘C as confirmed by X-ray diffraction. Strong LO-phonon Raman modes, especially B1g
(395 cm−1) and E
g
(636 cm−1) in Raman spectra and the absorption peak at 436 cm−1 in absorbance spectra by Fourier transform infrared spectroscopy also indicated the existence of anatase phase in crystalline
thin films. In addition, with the increase of the annealing temperature, the wettability of the film surface was enhanced
as shown by the decrease of water contact angle from over 90∘ to less than 40∘. Moreover, upon UV laser irradiation on film surface, the water contact angle saturated at 10∘ indicative of a highly hydrophilic surface for all the films, which arose from the dissociative adsorption of water molecules
on the defect sits of the surface generated by the photocatalysis reactions of TiO2. This behavior makes the film a good potential candidate for self-clean coatings. 相似文献
16.
The composite, consisting of two materials with different sensing temperatures, may show the selectivity for a particular gas. In this study, the microstructural and compositional effects on the electrical conductivity and the CO and the H2 gas sensing properties of SnO2-TiO2 composites were examined. SnO2-TiO2 composites in entire (0–100 mol%) composition range were fabricated in the form of porous pellet by sintering at 800C for 3 h. The effects of CuO-coating (or doping) on the electrical conductivity and the sensing properties to 200 ppm CO and H2 gases were examined.With CuO-coating, SnO2-TiO2 composites showed the increased sensitivity to CO gas and a large difference in the sensing temperatures between CO and H2 gases. As a result, CuO-coated SnO2-TiO2 composites showed the selectivity for CO gas between 100C and 190C and the selectivity for H2 gas between 280C and 380C. 相似文献
17.
Anatase TiO2 films were deposited on glass substrates at 50 and 200∘C to investigate the effect of growth temperature on the photocatalytic acitivity of the films. It was observed that the films
grown at 200∘C were composed of columnar crystallites and were more porous than the films grown at 50∘C which had more compact structures. Also, the film crystallinity increased from 75 to 90% if the higher growth temperature
was used. Despite the higher crystallinity, it was observed that for crystallinities between 60 and 90%, the photocatalytic
behavior of the films was more significantly affected by changes in the surface area. 相似文献
18.
Jong-Bong Lim Sahn Nahm Hyo-Tae Kim Jong-Hee Kim Jong-Hoo Paik Hwack-Joo Lee 《Journal of Electroceramics》2006,17(2-4):393-397
The effect of B2O3 and CuO on the sintering temperature and microwave dielectric properties of BaTi4O9 ceramics was investigated. The BaTi4O9 ceramics were able to be sintered at 975∘C when B2O3 was added. This decrease in the sintering temperature of the BaTi4O9 ceramics upon the addition of B2O3 is attributed to the formation of BaB2O4 second phase whose melting temperature is around 900∘C. The B2O3 added BaTi4O9 ceramics alone were not sintered below 975∘C, but were sintered at 875∘C when CuO was added. The formation of BaCu(B2O5) second phase could be responsible for the decrease in the sintering temperature of the CuO and B2O3 added BaTi4O9 ceramics. The BaTi4O9 ceramics containing 2.0 mol% B2O3 and 5.0 mol% CuO sintered at 900∘C for 2 h have good microwave dielectric properties of εr = 36.3, Q× f = 30,500 GHz and τf = 28.1 ppm/∘C 相似文献
19.
Yong Soo Cho Dong Joo Shin In June Kim Hyung Sub Lee Dong Suck Jeong 《Journal of Electroceramics》2006,17(2-4):461-465
The mixed system of BaTiO3 and AlN has been investigated in terms of dielectric properties and microstructure. Two different types of additives, bismuth
oxide and bismuth borosilicate glass, were used to lower sintering temperature. First, the addition of a fixed content (3
wt.%) of Bi2O3 provided densification at 1200∘C where monotonous decreases of dielectric constant were found with increasing the content of AlN. On the other hand, the
bismuth borosilicate glass was effectively used to decrease firing temperature to 850∘C, which is suitable for thick film capacitor applications. A practical demonstration of thick film capacitors using a Ag
electrode on a 96% alumina substrate indicated that the optimum composition of 76BaTiO3-20AlN-4glass may be adequate for generating k of 79.4 and tan δ of 0.014 at 1 MHz as a result of the low temperature firing
of 850∘C in air atmosphere. 相似文献
20.
The electric mechanisms of perovskite-type LaMnO3 was investigated with B-site substitution in this paper. Samples of La(TixMn1 − x)O3 (0.1 ≰ x ≰ 0.7) were sintered at different temperature. The voltage-temperature (V-T) curves of the samples were tested from room
temperature (25∘C) to 300∘C, then the electric properties were measured and analyzed. The experimental results showed that the resistivity-temperature
(ρ-T) curves of the samples matched NTC characteristic. The resistivity increased slightly with the increase of Ti amount as x was less than 0.5, however, it rose greatly after x exceeded 0.5; The sintering temperatures have a little influence on the resistivity, except for the sample with x = 0.7. 相似文献