共查询到20条相似文献,搜索用时 31 毫秒
1.
Choowong ChaisukAnusara Wehatoranawee Sirichai PreampiyawatSirirat Netiphat Artiwan Shotipruk Okorn Mekasuwandumrong 《Ceramics International》2011,37(5):1459-1463
Nanocrystalline TiO2, CeO2 and CeO2-doped TiO2 have been successfully prepared by one-step flame spray pyrolysis (FSP). Resulting powders were characterized with X-ray diffraction (XRD), N2-physisorption, Transmission Electron Microscopy (TEM) and UV-Vis spectrophotometry. The TiO2 and CeO2-doped TiO2 nanopowders were composed of single-crystalline spherical particles with as-prepared primary particle size of 10-13 nm for Ce doping concentrations of 5-50 at%, while square-shape particles with average size around 9 nm were only observed from flame-made CeO2. The adsorption edge of resulting powder was shifted from 388 to 467 nm as the Ce content increased from 0 to 30 at% and there was an optimal Ce content in association with the maximum absorbance. This effect is due to the insertion of Ce3+/4+ in the TiO2 matrix, which generated an n-type impurity band. 相似文献
2.
Co1−xZnxFe2O4 (0.1≤x≤0.9) nanorods have been prepared by the thermal decomposition of the corresponding oxalate precursor, which was synthesized by the template-, surfactant-free solvothermal method. The as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometry (VSM). The obtained Co1−xZnxFe2O4 (0.1≤x≤0.9) nanorods were built by many nanoparticles with average sizes around 20 nm to form one-dimensional arrays. Vibrating sample magnetometry measurements show that the coercivity of the ferrite nanorods decreases with increasing Zn content, whereas the specific saturation magnetization initially increases and then decreases with the increase of Zn content. The maximum saturation magnetization value of the as-prepared sample (Co0.5Zn0.5Fe2O4) reaches 43.0 emu g−1. 相似文献
3.
Haiyang Dai Xinyu Xie Zhenping Chen Fengjiao Ye Tao Li Yang Yang 《Ceramics International》2018,44(12):13894-13900
A series of multiferroic ceramics CuFe1-xEuxO2 (x?=?0–0.10) are prepared by traditional solid-state reaction. The effects of Eu doping on the microstructure, vacancy-type defects, and magnetic properties of CuFeO2 ceramics are investigated systematically by means of X-ray diffraction, Raman spectroscopy, scanning electron microscope, positron annihilation lifetime and physical property measurement system. The results show that no phase transition occurs in the entire range of doping content (x?=?0–0.10), but the single phase structure is damaged by high Eu content (x?=?0.04–0.10). Positron annihilation measurements indicate that the local electron density and the vacancy-type defect concentration increase gradually with the increase in Eu content from 0 to 0.08. Furthermore, abnormal changes in lifetime parameters can be found in x?=?0.10 sample induced by the existence of impurity phase in the system. The magnetic measurements reveal that all the samples exhibit two successive magnetic transitions at T?=?15 and 11?K. In x?=?0.02 sample, the coexistence of ferromagnetism and antiferromagnetism can be found, and a maximum saturation magnetization of 11.548?emu/g at 5?kOe is achieved. The possible reasons for the above observations are discussed in detail. 相似文献
4.
Nanosized particles of CoAlxFe2-xO4, where 0?≤?x?≤?2, were synthesized by the sol–gel combustion method and the magnetic properties of these compounds were investigated. According to X-ray diffractograms, the samples are single phase and the crystallite size is between 7 and 25?nm. The room temperature saturation magnetization of the samples was estimated from the cation distribution and ferromagnetic resonance spectra were used to determine the magnetocrystalline anisotropy. The results show that the saturation magnetization and the magnetocrystalline anisotropy vary over a wide range, from maxima of Ms =?0.42?MA/m and K?=?0.39?kJ/m3 for x?=?1.0 to minima of almost zero for x?≈?1.4, a result that could be useful for practical applications of these materials. 相似文献
5.
Rajjab Ali Muhammad Azhar Khan Azhar Mahmood Adeel Hussain Chughtai Amber Sultan Muhammad Shahid Muhammad Ishaq Muhammad Farooq Warsi 《Ceramics International》2014
Ca–Ni co-substituted samples of nanocrystalline spinel ferrites with chemical formula Mg1−xCaxNiyFe2−y O4 (x=0.0–0.6, y=0.0–1.2) were synthesized by the micro-emulsion method and were annealed at 700 °C for 7 h. The synthesized samples were characterized by x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, vibrating sample magnetometry (VSM) and dielectric measurements. The XRD and FTIR analysis reveals that single phase samples can be achieved by substituting Ca and Ni ions at Mg and Fe sites respectively in cubic spinel nano-ferrites. The crystallite size of the synthesized samples was found in the range 29–45 nm. The saturation magnetization (Ms) increases from 9.84 to 24.99 emu/g up to x=0.2, y=0.4 and then decreases, while the coercivity (Hc) increases continuously from 94 to 153 Oe with the increase in dopants concentration. The dielectric properties of these nano materials were also studied at room temperature in the frequency range 100 MHz to 3 GHz. The dielectric parameters were found to decrease with the increased Ca–Ni concentration. Further the peaking behavior was observed beyond 1.5 GHz. The frequency dependent dielectric properties of all the samples have been explained qualitatively on the basis of the Maxwell–Wagner two-layer model according to Koop's phenomenological theory. The enhanced magnetic parameters and reduced dielectric properties make the synthesized materials suitable for switching and high frequency applications, respectively. 相似文献
6.
Mário H.P. Santana 《Electrochimica acta》2006,51(17):3578-3585
A systematic investigation was conducted on the mechanism and electrocatalytic properties of O2 and Cl2 evolution on mixed oxide electrodes of nominal composition: Ti/[Ru(0.3)Ti(0.6)Ce(0.1−x)]O2[Nb2O5](x) (0 ≤ x ≤ 0.1). For the oxygen evolution, a 30 mV Tafel slope is obtained in the presence of CeO2, while in its absence a 40 mV coefficient is observed. The intrinsic electrocatalytic activity is mainly due to electronic factors, as result of the synergism between Ru and Ce oxides. For chlorine evolution, the Tafel slope (30 mV) is independent on oxide composition. The best global electrocatalytic activity for ClER was observed in the absence of Nb2O5 additive. Variation of the voltammetric charge throughout the experiments confirms high CeO2 content compositions are fragile, due mainly to the porosity caused by CeO2 presence. On the other hand, Nb2O5 addition decreases considerably this instability. 相似文献
7.
Rohit R. Powar Varsha D. Phadtare Vinayak G. Parale Hyung-Ho Park Sachin Pathak Pravin R. Kamble Pravina B. Piste Dnyanashwar N. Zambare 《Ceramics International》2018,44(17):20782-20789
In the present study, the chemical co-precipitation technique was adopted to synthesize ZnxCo1-xFe2O4 (ZCF) (0?≤ x?≤?1) ferrites. The thermogravimetric-differential thermal analysis results revealed that above 405?°C, the precursor had decomposed and ferrite formation had occurred. The structure and morphology of the prepared ferrite nanoparticles were investigated using X-ray diffraction, Fourier transform infrared spectroscopy, and field emission scanning electron microscopy (FE-SEM). The synthesized polycrystalline nanoparticles had a cubic spinel structure and the crystallite size was in the range of 6.09–12.98?nm. The prepared ferrites appeared as nearly spherical nanoparticles with a particle size in between 0.13 and 0.23?µm, as confirmed using FE-SEM. The elemental composition was determined using the energy-dispersive X-ray spectroscopy technique. The influence of the Zn-substituted cobalt ferrites (ZCF) on the structural, morphological, and magnetic properties were studied. The magnetic properties of the ZCF samples such as saturation magnetization, remanence magnetization, and coercivity measured at room temperature were 0.387–2.065?emu/g, 0.057–1.282?emu/g, and 60–1834?Oe, respectively. It was confirmed from the nature of the hysteresis loops that the given ZCF samples can be considered as a soft magnetic material. 相似文献
8.
A series of cerium dioxide (CeO2)/polyimide (PI) nanocomposites were successfully prepared from Ce(Phen)3 and polyamic acid (PAA) via the solution direct-dispersing method, followed by a step thermal imidization process. TGA and XPS studies showed that the cerium complex decomposed to form CeO2 during the thermal imidization process at 300 °C. SEM observation showed that the formed CeO2 as nanoparticles was well dispersed in polyimide matrix with a size of about 50-100 nm for samples with different contents of CeO2. Thermal analysis indicated that the introduction of CeO2 decreased the thermal stability of nanocomposite films due to the decomposition of Ce(Phen)3 in the imidization process, while the glass transition temperature (Tg) increased obviously, especially nanocomposite films with high loading of CeO2 exhibited a trend of disappearance of Tg. DMTA and static tensile measurements showed that the storage modulus of nanocomposite films increased, while the elongation at break decreased with increasing CeO2 content. 相似文献
9.
Magdalena Dudek Alicja Rapacz-Kmita Micha? Mosia?ek Grzegorz Mordarski 《Electrochimica acta》2010,55(14):4387-18997
The Pechinni method (A) as well as hydrothermal treatment (B) of co-precipitated CeO2-based gels with NaOH solution were used to synthesise pure CeO2, and CeO2-based solid solutions with formula Ce1−xMxO2, Ce1−x(M0.5Ca0.5)xO2 M = Gd, Sm for 0.15 < x < 0.3 nanopowders. The thermal evolution of CeO2-based precursors during heating them up to 1000 °C was monitored by thermal (TG, DTA) analysis and X-ray diffraction method. All nanopowders and samples sintered were found to be pure CeO2 or ceria-based solutions with fluorite-type structure. The microstructure of CeO2-based sintered samples at 1500 °C (A) or 1250 °C (B) was observed for 2 h under the scanning electron microscope. The electrical properties of singly Ce1−xMxO2 or doubly doped CeO2-based samples with formula Ce1−x(M0.5Ca0.5)xO2, M = Gd, Sm, 0.15 < x < 0.30 were investigated by means of the ac impedance spectroscopy method throughout the temperature range of 600-800 °C. It has been stated that partial substitution of calcium by samarium or calcium by gadolinium in the Ce1−x(M0.5Ca0.5)xO2, M = Gd, Sm solid solutions leads to ionic conductivity enhancement comparable with only samaria- or gadolina-doped ceria. The CeO2-based samples with small-grained microstructures obtained from powders synthesised by hydrothermal method exhibited better ionic conductivity than samples with the same composition obtained from powders synthesised by the Pechinii method. The stability of the electrolytic properties of selected co-doped ceria sinters in fuel gases (H2, CH4) as well as exhaust gases from diesel engine was also investigated. The co-doped Ce0.8(Sm0.5Ca0.5)0.2O2 or Ce0.85(Gd0.5Ca0.5)0.15O2 dense samples would appear be to more adequate oxide electrolytes than Ce1−xMxO2, M = Sm, Gd and x = 0.15 or 0.2 for electrochemical devices operating at temperatures ranging from 600 to 700 °C. 相似文献
10.
以凹凸棒石(ATP)为载体,Ce(NO3)3·6H2O和Ti(OBu)4为原料,冰醋酸为抑制剂,采用溶胶-凝胶法制备CeO2-TiO2/ATP纳米复合材料。利用TG-DSC、TEM、XRD和N2吸附/脱附仪对复合材料进行表征,考察铈钛摩尔比对所制备样品催化降解罗丹明B溶液性能的影响。结果表明,当Ce/Ti≥5/5时,具有立方萤石结构的氧化物颗粒以固溶体形式均匀分布在ATP表面,颗粒尺寸约5~10 nm;随Ti4+的进一步增加,样品中的CeO2结晶不完全;当Ce/Ti<3/7时,样品中出现锐钛矿型TiO2的分离相。适量的Ti4+掺杂能促进CeO2产生较多的结构缺陷,有利于增加晶格氧空位的浓度,提高样品的催化活性。对罗丹明B的催化降解实验表明,当Ce/Ti=5/5时,样品的催化性能较好,对罗丹明B溶液的化学需氧量(COD)去除率可达96%以上。 相似文献
11.
Honghong Lei Yuncheng Zhou Peng Jiang Wei Wang Wenbin Cao Yawen Xue 《Ceramics International》2018,44(16):19751-19755
Cr-doped Ba2In2-xCrxO5+y (0?≤?x?≤?0.5) orange-brown inorganic oxides have been successfully synthesized by solid-state reaction. X-ray diffraction (XRD) patterns show that their crystal structures transform from orthorhombic to cubic by increasing the Cr doping amount. Field emission scanning electron microscopy (FESEM) measurements show powder particles of irregular shape with average particle size of about 10?µm. The colors of the compounds are tuned from light yellow (x?=?0) to orange (x?=?0.1) and then to dark brown (x?=?0.5). X-ray photoelectron spectroscopy and UV–Vis absorption spectroscopy demonstrate the oxidation state of Cr to be +?6 and the change in color to be due to the metal-ligand charge transfer of Cr6+-O2-. 相似文献
12.
Dengwei Hu Fan Zhao Zhen Zhang Lei Miao Rong Ma Weixing Zhao Lijun Ren Gaini Zhang Le Zhai Dongmei Wang Shumei Dou 《Ceramics International》2018,44(18):22462-22466
The monodisperse CoFe2O4 nanoparticles were synthesized by a modified chemical coprecipitation method. Coating SiO2 on the surface of the CoFe2O4 nanoparticles was carried out to keep single domain particles non-interacting with cubic magnetocrystalline anisotropy. The Curie temperatures (Tc) of the monodisperse CoFe2O4 nanoparticles can be accurately measured because the SiO2 shells prevented the aggregation and growth of nanoparticles at high temperature. The magnetic properties of the CoFe2O4@SiO2 nanoparticles with core-shell structure in a wide temperature range (300~950?K) were investigated. It is remarkable that the coercive field (Hc) of CoFe2O4 nanoparticles increased from about 760?Oe to 1806?Oe after being coated with SiO2, which increased by 137.6% compared to the uncoated samples at 300?K. The saturation magnetization (Ms) of the CoFe2O4@SiO2 nanoparticles is 34.59?emu/g, which is about 52% of the naked CoFe2O4 nanoparticles value (66.51?emu/g) at 300?K. The hysteresis loops of the CoFe2O4@SiO2 nanoparticles showed an orderly magnetic behavior at high temperature, such as the Ms, remanence magnetization (Mr) and Hc decreased as temperature increasing, being equal to zero near Tc. This is a good indication that the CoFe2O4@SiO2 nanoparticles are suitable for a wide variety of technological applications at high temperature. 相似文献
13.
Imad Hussain S.N. Khan Eun Ji Kim So Eun Jeon Bon Heun Koo 《Ceramics International》2018,44(3):2892-2899
A systematic study focusing on the effect of Niobium (Nb) doping on the structural, magnetic and magnetocaloric properties of Ba2FeMoO6 samples is presented here. The samples of interest Ba2FeMo1?xNbxO6 (0 ≤ x ≤ 0.4) were prepared using the solid state reaction method and were confirmed to possess a cubic structure with Fm-3m space group using the X-ray diffraction analysis and Rietveld refinement. A second order of ferromagnetic phase transition was recorded in both the pure as well as the Nb doped samples using the temperature dependent magnetization and Arrott plots analysis. The pristine Ba2FeMoO6 (BFMO) sample indicated a spontaneous magnetization (34.6 emu/g at 100 K) with a relatively sharp magnetic transition at the Curie temperature (TC) of 315 K as compared to the doped samples. A magnetic entropy change of 0.93 Jkg?1K?1 at an applied magnetic field of 2.5 T was measured for the pure BFMO sample. The doped BFMO samples with Mo partially substituted by Nb however, were observed to effectively modify the TC accompanied by a decrease in magnetization. The results investigated in this work suggest that the magnetic and magnetocaloric properties of the BFMO can be tailored by controlled Nb doping which is of significant importance in order to realize the numerous potential applications of the material in the magnetic refrigeration technology. 相似文献
14.
Izabela Dobrosz-Gmez Ireneusz Kocemba Jacek M. Rynkowski 《Applied catalysis. B, Environmental》2008,83(3-4):240-255
The physico-chemical properties and activity of Ce-Zr mixed oxides, CeO2 and ZrO2 in CO oxidation have been studied considering both their usefulness as supports for Au nanoparticles and their contribution to the reaction. A series of Ce1−xZrxO2 (x = 0, 0.25, 0.5, 0.75, 1) oxides has been prepared by sol–gel like method and tested in CO oxidation. Highly uniform, nanosized, Ce-Zr solid solutions were obtained. The activity of mixed oxides in CO oxidation was found to be dependent on Ce/Zr molar ratio and related to their reducibility and/or oxygen mobility. CeO2 and Ce0.75Zr0.25O2, characterized by the cubic crystalline phase show the highest activity in CO oxidation. It suggests that the presence of a cubic crystalline phase in Ce-Zr solid solution improves its catalytic activity in CO oxidation. The relation between the physico-chemical properties of the supports and the catalytic performance of Au/Ce1−xZrxO2 catalysts in CO oxidation reaction has been investigated. Gold was deposited by the direct anionic exchange (DAE) method. The role of the support in the creation of catalytic performance of supported Au nanoparticles in CO oxidation was significant. A direct correlation between activity and catalysts reducibility was observed. Ceria, which is susceptible to the reduction at the lowest temperature, in the presence of highly dispersed Au nanoparticles, appears to be responsible for the activity of the studied catalysts. CeO2-ZrO2 mixed oxides are promising supports for Au nanoparticles in CO oxidation whose activity is found to be dependent on Ce/Zr molar ratio. 相似文献
15.
We have prepared Ba1-xSrxCoFe11O19 hexaferrite nanoparticles (NPs) by using a co-precipitation method. The crystal/electronic structures and magnetic properties were then studied. Results revealed that all Ba1-xSrxCoFe11O19 NPs with particle sizes of 100–300?nm crystallized in a hexagonal structure. Both the particle shape and the unit-cell parameters are changed when Sr content (x) increases. The analysis of the electronic structure based on the Fe and Co K-edge XAS spectra proved the oxidation states of Fe and Co to be 3?+?and 2?+?, respectively, which are stable versus an x change in Ba1-xSrxCoFe11O19. Local-structural studies also revealed the average bond length between Fe and O of 1.89–1.91?Å less changed by Sr doping. Though the electronic structures of Fe and Co were unchanged, the studies about the magnetic property demonstrated a strong dependence of Ms and Hc on Sr doping. While Ms decreases from 46.1?emu/g for x?=?0–34.2?emu/g for x?=?1, Hc tends to increase from 1630?Oe for x?=?0 to ~ 2200?Oe for x?=?0.5, but slightly decreases to 2040?Oe for x?=?1. We think that the addition of the exchange interaction between Fe3+ and Co2+ ions and the changes of local-geometric structures and microstructures influenced directly Ms and Hc of NPs. 相似文献
16.
(1 − x)Ba0.6Sr0.4TiO3-xMgAl2O4(x = 25, 30, 35 and 40 wt%) composite ceramics were prepared by conventional solid-state reaction method. The microstructures, dielectric properties and tunability of the composites have been investigated. The XRD patterns analysis reveals two crystalline phases, a cubic perovskite structure Ba0.6Sr0.4TiO3 (BST) and a spinel structure MgAl2O4 (MA). SEM observations show that the BST grains slightly dwindle and agglomerate with increasing amounts of MA. A dielectric peak with very strong frequency dispersion is observed at higher MA content, and the Curie temperature shifts to a higher temperature with increasing MA content. The ceramic sample with 30 wt% MA has the optimized properties: the dielectric constant is 1503, the dielectric loss is 0.003 at 10 kHz and 25 °C, the tunability is 23.63% under a dc electric field of 1.0 kV/mm, which is suitable for ferroelectric phase shifter. 相似文献
17.
Improvement of electrochemical stability of LiMn2O4 by CeO2 coating for lithium-ion batteries 总被引:1,自引:0,他引:1
Hyung-Wook Ha 《Electrochimica acta》2007,52(9):3236-3241
CeO2-coated LiMn2O4 spinel cathode was synthesized using two-step synthesis method. All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns. The results of the electrochemical performances on CeO2-coated electrode are compared to those of electrodes based on LiMn2O4 spinel without CeO2 coating. CeO2-coated LiMn2O4 cathode improved the cycling stability of the electrode. The capacity retention of 2 wt% CeO2-coated LiMn2O4 was more than 82% after 150 cycles between 3.0 and 4.4 V at room temperature and 82% after 40 cycles at elevated temperature of 60 °C. The amounts of dissolved manganese-ions in CeO2-coated LiMn2O4 significantly are smaller than pristine LiMn2O4 systems especially at elevated temperatures. Surface-modified LiMn2O4 can suppress the dissolution reaction of manganese-ions at elevated temperature and clearly improve the cyclability of the spinel LiMn2O4 cathode materials. 相似文献
18.
César O. Avellaneda Diogo F. Vieira Edson R. Leite Michel A. Aegerter 《Electrochimica acta》2007,53(4):1648-1654
A gelatin-based electrolyte has been developed and characterized by impedance spectroscopy, X-ray diffraction, UV-vis-NIR spectroscopy and atomic force microscopy (AFM). The heat treatment temperature was found the key factor affecting its ionic conductivity that increases from 1.5 × 10−5 S/cm to 4.9 × 10−4 S/cm by heating from room temperature up to 80 °C. The temperature dependence of the ionic conductivity exhibits an Arrhenius behavior. EC-devices with the configuration K-glass/Nb2O5:Mo EC-layer/gelatin-based electrolyte/(CeO2)x(TiO2)1−x ion-storage (IS) layer/K-glass, have been assembled and characterized. They show a good long time cyclic stability, but the change of the optical density measured at 550 nm after 25 000 cycles was only 0.13. 相似文献
19.
Nanostructured CeO2/CuO composites are synthesized using a facile hydrothermal reaction. Results signify that Cu ions prefer to enter into CeO2 lattice forming solid solution at low concentration, and would be transformed into CuO phase at moderate concentration. Moreover, the addition of CuO species into CeO2 promotes the reduction of Ce4+ and the creation of oxygen vacancy (VO) defects. Raman analyses confirm VO concentration initially increases and then decreases with the increasing CuO phase and the sample Ce1Cu2 exhibits the highest defect concentration. The room temperature ferromagnetic behavior is observed firstly in CeO2/CuO nonmagnetic system and the maximal saturation magnetization appears in Ce1Cu2. The emergent ferromagnetism appears to be relevant to the extensive VO defects, which can be interpreted by the indirect double-exchange model. The synthetic interaction between CeO2 and CuO results in the redshift of the bandgap in prepared CeO2/CuO nanocomposites. 相似文献
20.
Mohammad Javad Nasr Isfahani Parisa Nasr IsfahaniKlebson Lucenildo Da Silva Armin FeldhoffVladimir Šepelák 《Ceramics International》2011,37(6):1905-1909
NiFe2−xBixO4 (x = 0, 0.1, 0.15) nanopowders were synthesized via sol-gel method. The precursor gels were calcined at 773 K in air for 1 h to obtain the pure nanostructured NiFe2−xBixO4 spinel phase. The crystal structure and magnetic properties of the substituted spinel series of NiFe2−xBixO4 have been investigated by means of 57Fe Mössbauer spectroscopy, transmission electron microscopy and alternating gradient force magnetometry. Mössbauer spectroscopic measurements revealed that Bi3+ cations tend to occupy octahedral positions in the structure of the substituted ferrite, i.e., the crystal-chemical formula of the as-prepared nanoparticles may be written as: (Fe)[NiFe1−xBix]O4 (x = 0, 0.1, 0.15), where parentheses and square brackets enclose cations on sites of tetrahedral and octahedral coordination, respectively. Selective area electron diffraction studies provided evidence that the samples of the NiFe2−xBixO4 series, independently of x, exhibit the cubic spinel structure. The values of the saturation magnetization and the coercive field of NiFe2−xBixO4 nanoparticles were found to decrease with increasing degree of bismuth substitution. 相似文献