共查询到20条相似文献,搜索用时 62 毫秒
1.
Guo-hua Chen Jun-tao Liu Hua-rui Xu Chang-rong Zhou Min-hong Jiang Xin-yu Liu 《Journal of Materials Science: Materials in Electronics》2011,22(8):915-919
Ultrafine strontium barium niobate (Sr0.3Ba0.7Nb2O6, SBN30) powders were prepared by urea method starting from a precursor solution constituting of Sr (NO3)2, Ba (NO3)2, NbF5, urea and polyvinyl alcohol (PVA) as surfactant. Their structural behavior and morphology were examined by means of X-ray
diffractometry (XRD) and Scanning electron microscopy (SEM). The results showed that the SBN30 powders crystallized to a pure
tetragonal phase at annealing temperatures as low as 750 °C. The average particle size of SBN powders subjected to 750 °C
was of the order of 150–300 nm. With increasing calcination temperature,however, the average particle size of the calcined
powders increased. The SBN30 ceramic prepared from urea method can be sintered at temperature as low as 1,225 °C. The transition
temperature from the ferroelectric phase to the paraelectric phase and the relative dielectric permittivity of the SBN30 powder
were less than the corresponding values of the bulk ceramic. The permittivity and loss tangent (tan δ) at room temperature
(1 kHz) was found to be 930 and below 0.025. 相似文献
2.
P. Thomas L. N. Sathapathy K. Dwarakanath K. B. R. Varma 《Bulletin of Materials Science》2007,30(6):567-570
CaCu3Ti4O12 (CCTO) was synthesized and sintered by microwave processing at 2·45 GHz, 1·1 kW. The optimum calcination temperature using
microwave heating was determined to be 950°C for 20 min to obtain cubic CCTO powders. The microwave processed powders were
sintered to 94% density at 1000°C/60 min. The microstructural studies carried out on these ceramics revealed the grain size
to be in the range 1–7 μm. The dielectric constants for the microwave sintered (1000°C/60 min) ceramics were found to vary
from 11000–7700 in the 100 Hz–00 kHz frequency range. Interestingly the dielectric loss had lower values than those sintered
by conventional sintering routes and decreases with increase in frequency. 相似文献
3.
A. Beitollahi H. Hosseini-Bay H. Sarpoolaki 《Journal of Materials Science: Materials in Electronics》2010,21(2):130-136
Nanocrystalline alumina–zirconia powders were prepared by a modified chemical route using sucrose, polyvinyl alcohol (PVA)
and metal nitrates followed by a post calcination process. The process involved dehydration of Al3+–Zr4+ ions-sucrose–PVA solution to a highly viscous liquid which on decomposition process produced a black precursor material.
The obtained precursor were then calcined at various temperatures: 1,050, 1,100, 1,150, 1,200 and 1,250 °C for different soaking
times (1, 2, 4 h) in air. The formation of a nanocomposite composed of α-alumina (~20 nm) and tetragonal (t) zirconia (~19 nm) crystallites were confirmed for the sample calcined at 1,200 °C for 2 h, based on our XRD and TEM results.
However, for the samples calcined below 1,150 °C the composite formed were composed of metastable alumina (γ, δ, θ) as well as t-zirconia phases. Interestingly, the zirconia phase retained its tetragonal structure for all the samples calcined above 1,050 °C.
This is possibly related to the “size effect” and reduction of surface enthalpy of the zirconia crystallites surrounded by
Al3+ cations. 相似文献
4.
A. B. Bodade Minaz Alvi A. V. Kadu G. N. Chaudhari 《Journal of Materials Science》2010,45(19):5264-5270
Nanocrystalline La1−x
Co
x
Mn1−y
Ni
y
O3 (x = 0.2 and 0.4; y = 0.1, 0.3, and 0.5) thick films sensors prepared by sol–gel method were studied for their H2S gas sensitivity. The structural and morphological properties have been carried out by X-ray diffraction (XRD) and transmission
electron microscopy (TEM). Average particle size estimated from XRD and TEM analyses was observed to be 30–35 nm. The gas
response characteristics were found to depend on the dopants concentration and operating temperature. The maximum H2S gas response of pure LaMnO3 was found to be at 300 °C. In order to improve the gas response, material doped with transition metals Co and Ni on A- and
B-site, respectively. The La0.6Co0.4Mn0.5Ni0.5O3 shows high response towards H2S gas at an operating temperature 250 °C. The Pd-doped La0.6Co0.4Mn0.5Ni0.5O3 sensor was found to be highly sensitive to H2S at an operating temperature 200 °C. The gas response, selectivity, response time and recovery time were studied and discussed. 相似文献
5.
Huanfu Zhou Xiuli Chen Liang Fang Changzheng Hu Hong Wang 《Journal of Materials Science: Materials in Electronics》2010,21(9):939-942
Ba5Nb4O15 powders were synthesized by molten-salt method in NaCl–KCl flux at a low temperature of 650–900 °C for 2 h, which is lower
than that of the conventional solid-state reaction. This simple process involved mixing of the raw materials and salts in
a certain proportion. Subsequent calcination of the mixtures led to Ba5Nb4O15 powders at 650–900 °C. XRD and SEM techniques were used to characterize the phase and morphology of the fabricated Ba5Nb4O15 powders, respectively. After sintering at 1,300 °C for 2 h, the densified Ba5Nb4O15 ceramics with good microwave dielectric properties of εr = 39.2, Q × f approximated as 27,200 GHz and τ
f
= 72 ppm/°C have been obtained. 相似文献
6.
B. S. Shirke P. V. Korake P. P. Hankare S. R. Bamane K. M. Garadkar 《Journal of Materials Science: Materials in Electronics》2011,22(7):821-824
Pure anatase TiO2 nanoparticles were synthesized by microwave assisted sol–gel method and further characterized by powder X-ray diffraction
(XRD), energy dispersive x-ray analysis (EDAX), scanning electron microscopy (SEM), transmission electron microscopy (TEM),
and UV–Visible spectrophotometer, SEM images showed that TiO2 nanoparticles were porous structure. The XRD patterns indicated that TiO2 after annealed at 300 °C for 3 h was mainly pure anatase phase. The crystallite size was in the range of 20–25 nm, which
is consistent with the results obtained from TEM images. Microwave heating offers several potential advantages over conventional
heating for inducing or enhancing chemical reactions. 相似文献
7.
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
8.
C. Kumar 《Journal of Materials Science: Materials in Electronics》2011,22(6):579-582
The preparation of Calcium copper titanate (CCTO) nanopowder was carried out by a sol–gel self combustion method. The X-ray
diffraction analysis indicated that the samples calcined at 800 °C were fully crystallized in the CCTO phase. The results
of atomic force microscope showed the particles size of CCTO was in the range of 60–80 nm. The absorption bands corresponding
to vibrations of Cu–O, Ti–O–Ti and νCa–O were observed at 512, 450 and 562 cm−1 using FTIR. The samples sintered at 950 °C showed the densities as high as 97% of theoretical density. The grain sizes of
sintered pellets were determined by HRSEM. The dielectric properties of prepared samples were studied by LCR meter. 相似文献
9.
Joshua T. White Ivar E. Reimanis James R. O’Brien 《Journal of Materials Science》2012,47(4):1690-1696
The solubility of NiO in ZrO2 was studied by X-ray diffraction, TEM, and SQUID magnetometry. Lattice parameter measurements from a similar, established
oxide system, NiO−10YSZ, were first used to show that SQUID magnetometry can effectively measure solubility. ZrO2 specimens with 0, 0.5, 1, 2, 3, and 5 percent by mol NiO were prepared via the Pechini method. The specimens were calcined
in air at 500, 600, and 1000 °C. The paramagnetic response of the specimens measured with SQUID magnetometry revealed that
up to 5 percent by mol NiO is soluble in ZrO2 for specimens calcined at 500 and 600 °C. The relatively large solubility compared with NiO−10YSZ occurs due to the very
fine grain size (5–10 nm). The fine grain size is also responsible for stabilizing the tetragonal phase of ZrO2. At the 1000 °C calcination temperature, the ZrO2 is entirely monoclinic, exhibits larger grains (>45 nm), and only dissolves about 0.5 percent by mol or less NiO. The correlations
between grain size, ZrO2 polytype, and NiO addition are discussed. 相似文献
10.
Ternary perovskite ceramics of Pb[(Zr0.5Ti0.5)0.8−x
(Mg1/3Nb2/3)0.2+x]0.98Nb0.02O3.01 (PZTMN, x = −0.075, −0.05, −0.025, 0, 0.025, 0.05, and 0.075 ), are synthesized via dry–dry method. B-site precursors of PZTMN ([(Zr0.5Ti0.5)0.8−x
(Mg1/3Nb2/3)0.2+x
]0.98Nb0.02O2.01, ZTMN) can be synthesized via a two-step solid state reaction method. The first calcination temperature is 1,300 °C, and
the second is not higher than 1,360 °C. Incorporation of magnesium and niobium ions promotes the formation of the single phase
solid solution with ZrTiO4 structure. Single phase perovskite PZTMN is formed at 780 °C, much lower than that in conventional process. Dense ceramics
can be sintered at about 1,260 °C with dielectric and piezoelectric properties comparable to that of wet–dry method and higher
than that of conventional method. It seems that B-site precursor method is cost effective in preparation of ternary piezoelectric
ceramics. 相似文献
11.
N. T. Gurin K. V. Paksyutov M. A. Terent’ev A. V. Shirokov 《Technical Physics Letters》2008,34(11):905-907
Glassy-crystalline samples of compositions (B2O3-Al2O3-SiO2):Eu2+ (3 at %) and (B2O3-2SiO2):Eu2+ (3 at %) were obtained by sintering the initial powdered mixtures at 1300°C in air. Being excited by laser radiation at a
wavelength of 325 nm, the former samples exhibit intense blue photoluminescence with a maximum at 434–448 nm, while the latter
samples emit in the violet spectral interval with a maximum at 409 nm. An increase in the content of B2O3 leads to a shift of the emission maximum toward a shorter wavelength, while additional annealing at 1300°C C in vacuum shifts
the spectrum toward longer wavelengths. 相似文献
12.
Mesoporous electrode materials of spinel Co3O4 were synthesized by hydrothermal method using polyethylene glycol-6000 (PEG-6000) as dispersant and subsequent calcination
at different temperatures in air. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron
microscopy (FESEM), nitrogen adsorption and electrochemical measurements. The results showed that the dispersant PEG-6000
had a distinct effect to control the porosity, particle size and homogeneity of Co3O4; the calcination temperature had a significant influence on the crystal structure, surface area, porosity and morphology,
and indeed electrochemical performance. The resultant Co3O4 sample calcinated at 350° C possessed a narrow mesopore distribution around 4 nm and exhibited excellent electrochemical
performance. It had the specific capacitance as high as 348.7 F/g, increased by 21.5% over that of pure Co3O4 and showed good cyclical charge–discharge stability. 相似文献
13.
Dunmin Lin Qiaoji Zheng K. W. Kwok Chenggang Xu Chun Yang 《Journal of Materials Science: Materials in Electronics》2010,21(7):649-655
Lead-free MnO2-doped K0.5Na0.5Nb0.92Sb0.08O3 ceramics have been fabricated by a conventional ceramic technique and their dielectric and piezoelectric properties have
been studied. Our results show that a small amount of MnO2 (0.5–1.0 mol%) is enough to improve the densification of the ceramics and decrease the sintering temperature of the ceramics.
The co-effects of MnO2 doping and Sb-substitution lead to significant improvements in the ferroelectric and piezoelectric properties. The K0.5Na0.5Nb0.92Sb0.08O3 ceramic with 0.5 mol%MnO2 doping possesses optimum propeties: d
33 = 187 pC/N, k
P = 47.2%, ε
r = 980, tanδ = 2.71% and T
c = 287 °C. Due to high tetragonal-orthorhombic phase transition temperature (T
O-T ~ 150 °C), the K0.5Na0.5Nb0.92Sb0.08O3 ceramic with 0.5 mol%MnO2 doping exhibits a good thermal stability of piezoelectric properties. 相似文献
14.
Synthesis of nano-MoS<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> composite and its catalytic degradation effect on methyl orange 总被引:1,自引:0,他引:1
A nano-MoS2/TiO2 composite was synthesized in H2 atmosphere by calcining a MoS3/TiO2 precursor, which was obtained via a quick deposition of MoS3 on anatase nano-TiO2 under a strong acidic condition. The obtained nano-MoS2/TiO2 composite was characterized by X-ray diffraction spectroscopy, Brunauer–Emmett–Teller (BET) surface area, scanning electron
microscopy, high-resolution transmission electron microscopy, energy-dispersive spectrometry, ultraviolet–visible spectroscopy,
and Fourier transform infrared spectroscopy. The results show that the composite had a high BET surface area because of its
small size and irregularly layered structure. MoS2 in the composite was composed of typical layered structures with thicknesses of 2–8 nm and lengths of 10–40 nm. The composite
contained a wide and intensive absorption at 400–700 nm, which is in the visible light region, and presented a positive catalytic
effect on removing methyl orange from the aqueous solution. The catalytic activity of the composite was influenced by the
initial concentration of methyl orange, the amount of the catalyst, the pH value, and the degradation temperature. In addition,
the composite catalyst could be regenerated and repeatedly used via filtration three times. The deactivating catalyst could
be reactivated after catalytic reaction by heating at 450 °C for 30 min in H2. 相似文献
15.
T. Joseph S. Uma J. Philip M. T. Sebastian 《Journal of Materials Science: Materials in Electronics》2011,22(8):1000-1009
A new polymer-ceramic composite was prepared using PTFE and low loss Sr2ZnSi2O7. The dielectric properties of the composite were studied in the microwave and radiofrequency ranges. The relative permittivity
(εr) and dielectric loss (tan δ) increased with the filler loading from 0.10 to 0.50 volume fractions (vf). The observed values of εr, thermal conductivity and coefficient of thermal expansion (CTE) were compared with the corresponding theoretical predictions.
The ability of the composite towards moisture absorption resistance was studied as a function of filler loading. It was also
found that the variation of εr was less than 2% in the temperature range 25–90 °C, at 1 MHz. For a filler content of 0.50 vf, the PTFE/Sr2ZnSi2O7 composite exhibited εr = 4.4, tan δ = 0.003 (at 4–6 GHz), CTE = 38.3 ppm/°C, thermal conductivity = 2.1 W/mK and moisture absorption = 0.09 wt%. 相似文献
16.
GUO-HUA CHEN JIN LIU XU-QIONG LI HUA-RUI XU MIN-HONG JIANG CHANG-RONG ZHOU 《Bulletin of Materials Science》2011,34(6):1233-1236
Phase purity, microstructure, sinterability and microwave dielectric properties of BaCu(B2O5)-added Li2ZnTi3O8 ceramics and their cofireability with Ag electrode were investigated. A small amount of BaCu (B2O5) can effectively reduce the sintering temperature from 1075°C to 925°C, and it does not induce much degradation of the microwave
dielectric properties. Microwave dielectric properties of ε
r = 23·1, Q × f = 22,732 GHz and τ
f = − 17·6 ppm/°C were obtained for Li2ZnTi3O8 ceramic with 1·5 wt% BaCu(B2O5) sintered at 925°C for 4 h. The Li2ZnTi3O8 +BCB ceramics can be compatible with Ag electrode, which makes it a promising microwave dielectric material for low-temperature
co-fired ceramic technology application. 相似文献
17.
Based on the principle of stability of geopolymer gel as refractory binder, a geopolymeric paste in the K2O–Al2O3–SiO2 system was developed and used to produce refractory concretes by adding various amount of α-quartz sand (grain size in the
range 0.1 μm to 1 mm) and fine powder alumina (grain size in the range 0.1–100 μm). The consolidated samples were characterized
before and after sintering using optical dilatometer, DSC, XRD and SEM. The total shrinkage in the range of 25–900 °C was
less than 3%, reduced with respect to the most diffused potassium or sodium based geopolymer systems, which generally records
a >5% shrinkage. The maximum shrinkage of the basic geopolymer composition was recorded at 1000 °C with a 17% shrinkage which
is reduced to 12% by alumina addition. The temperature of maximum densification was shifted from 1000 °C to 1150 or 1200 °C
by adding 75 wt% α-quartz sand or fine powder alumina respectively. The sequences of sintering of geopolymer concretes could
be resumed as dehydration, dehydroxylation, densification and finally plastic deformation due to the importance of liquid
phase. The geopolymer formulations developed in this study appeared as promising candidates for high-temperature applications:
refractory, fire resistant or insulating materials. 相似文献
18.
The manganese iron cyclotetraphosphate (MnFeP4O12) was synthesized through one-step thermal synthesis at 700 °C using the mixing of manganese and iron metals and phosphoric
acid in the presence of water–acetone media. Both FTIR and XRD results indicate the cyclotetraphosphate (P4O12
4−) structure and a pure monoclinic phase with space group C2/c (Z = 4). The morphology and crystallite size for the MnFeP4O12 obtained from SEM data and X-ray line broadening show non-uniform particles and 30 ± 9 nm, respectively. The magnetic study
of the synthesized MnFeP4O12 shows superparamagnetic behavior, which is important for specific application. Some physical properties of the synthesized
MnFeP4O12 powder presented for the first time are comparable with those from individual M2P4O12 (M = Mn and Fe) and a binary metal compound as CoFeP4O12. 相似文献
19.
Prasanta Dhak Debasis Dhak Manasmita Das Panchanan Pramanik 《Journal of Materials Science: Materials in Electronics》2011,22(12):1750-1760
Nanocrystalline ceramic powder of Ba0.8Bi2.133Nb1.6Ta0.4O9 was synthesized by chemical precursor decomposition method. The single-phase formation of the compound was confirmed using
an X-ray diffraction technique and was found to be a tetragonal phase at room temperature. Average crystallite size and particle
size were found to be 41 and 48.5 nm, which were analyzed through XRD and TEM respectively. The dielectric constant and tangent
loss were measured in the frequency range 1 kHz–1 MHz after sintering the sample at 900 °C for 4 h. The polarization behavior
was studied at an applied voltage of 6.2 kV/cm. Electrical properties of the material were investigated using complex impedance
spectroscopy (CIS) technique, which revealed the presence of both grain and grain-boundary effects in the materials, which
is also evidenced from the scanning electron microscope image. Grain conductivity indicated Arrhenius-type thermally activated
process. AC conductivity spectrum obeys Jonscher’s universal power law. The electric modulus analysis suggests the possibility
of hopping mechanism for electrical processes in the system with a non-debye type relaxation, which is supported by the impedance
data. 相似文献
20.
Sachin Tyagi Ramesh Chandra Agarwala Vijaya Agarwala 《Journal of Materials Science: Materials in Electronics》2011,22(8):1085-1094
Nickel substituted strontium hexaferrite, SrFe11.2Ni 0.8O19 nanoparticles having super paramagnetic nature were synthesised by co-precipitation of chloride salts using 7.5 M sodium
hydroxide solution. The resulting precursors were heat treated (HT) at 900 and 1,200 °C for 4 h in nitrogen atmosphere. During
heat treatment, transformation proceeds as a constant rate of nucleation and three dimensional growth with activation energy
of 183.724 kJ/mole. The hysteresis loops showed an increase in saturation magnetization from 1.045 to 65.188 emu/g with increasing
HT temperatures. The ‘as-synthesised’ particles have size in the range of 20–25 nm with spherical and needle shapes. Further,
these spherical and needle shaped nanoparticles tend to change their morphology to hexagonal plates with increase in HT temperatures.
The effect of such a systematic morphological transformation of nanoparticles on dielectric (complex permitivity and permeability)
and microwave absorption properties were estimated in X band (8.2–12.2 GHz). The maximum reflection loss of the composite
powder reaches −24.92 dB at the thickness of 2.2 mm which suits its application in RADAR absorbing materials. 相似文献