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ABSTRACT: Barium titanate nanoparticles with various nominal Ba/Ti ratios were prepared through direct synthesis from solution (DSS)
and further annealed at different temperatures. Their deviation from stoichiometry was studied through XRD analysis, and a
large deviation from stoichiometry has been observed. The grain size we studied ranges from 50nm to 1μm. For the as-prepared
particles, the grain size is about 50nm, and the maximum excess of Ti is over 15%. For the samples annealed at 800°C, the
grain size is increased to 100nm, and the maximum excesses of Ba and Ti are 8 and 9%, respectively. The defects formed during
synthesis and surface effect of nanoparticles are both estimated for their contributions to the deviation from stoichiometry,
and the defects have been found to be mainly responsible for the large deviation observed.
KeywordsBarium titanate-Nanoparticle-Stoichiometry-Ba/Ti ratio-Synthesis-Colloids
Journal of Nanoparticle Research 04/2012; 12(7):2605-2609. · 3.29 Impact Factor
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ABSTRACT: ABSTRACT: A large quantity of ultrafine tetragonal barium titanate (BaTiO3) nanoparticles is directly synthesized at room temperature. The crystalline form and grain size are checked by both X-ray diffraction and transmission electron microscopy. The results revealed that the perovskite nanoparticles as fine as 7 nm have been synthesized. The phase transition of the as-prepared nanoparticles is investigated by the temperature-dependent Raman spectrum and shows the similar tendency to that of bulk BaTiO3 materials. It is confirmed that the nanoparticles have tetragonal phase at room temperature.
Nanoscale Research Letters 01/2011; 6(1):466. · 2.73 Impact Factor
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ABSTRACT: This article presents a new lost mold rapid prototyping method which combines selective laser sintering (SLS) and gelcasting techniques for fabricating piezoelectric ceramics. SLS was used to fabricate sacrificial molds of the desired structure of the ceramic part. Then aqueous PZT (lead zirconate titanate) suspension was cast in the mold and solidified in situ through formation of a three-dimensional network gel. Because the polymer mold can be easily removed at the initial stage of sintering and the gelcast PZT body has a high green strength, the desired geometry of the PZT part can be completely retained after sintering of the ceramics. Complex-shaped PZT parts were successfully fabricated after using concentrated PZT suspension with low viscosity. Densities and electrical properties, such as the d33, the relative permittivity ε, the dielectric loss tgδ and the electromechanical coupling factor Kp of the gelcast PZT parts were also compared with those of the die-pressed PZT samples. The results indicated that the gel-forming process did not deteriorate the electrical properties of the samples, if proper dispersant was selected in developing concentrated ceramic slurry.
Journal of the American Ceramic Society 06/2008; 87(1):17 - 22. · 2.27 Impact Factor
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ABSTRACT: Here we report a very simple method to convert conventional CuO powders to nanoparticle interlinked microsphere cages by solution
method. CuO is dissolved into aqueous ammonia, and the solution is diluted by alcohol and dip coating onto a glass substrate.
Drying at 80°C, the nanostructures with bunchy nanoparticles of Cu(OH)2 can be formed. After the substrate immerges into the solution and we vaporize the solution, hollow microspheres can be formed
onto the substrate. There are three phases in the as-prepared samples, monoclinic tenorite CuO, orthorhombic Cu(OH)2, and monoclinic carbonatodiamminecopper(II) (Cu(NH3)2CO3). After annealing at 150°C, the products convert to CuO completely. At annealing temperature above 350°C, the hollow microspheres
became nanoparticle interlinked cages.
Nanoscale Research Letters 01/2007; 2(2):107-111. · 2.73 Impact Factor
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ABSTRACT: CuFe2O4 nanowalls with a thickness of 10 nm are directly fabricated from CuFe2O4 ceramic grains on the surface of the ceramic at the cathode by an electrochemical method. During this fabrication period, some of the Cu2+ will be reduced to Cu metal and released from the lattice; at the same time, some of the Fe3+ will be reduced to Fe2+ and this will lead to cation rearrangement and a phase transition from tetragonal to cubic structure. Release of copper from the lattice and lattice cell shrinkage during the phase transition are found to be responsible for the imposing of stress in the surface layer of the sample and the formation of the nanowalls.
Nanotechnology 11/2005; 16(12):3097. · 3.98 Impact Factor
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ABSTRACT: Transparent copper nanorod/nanowire arrays and anodic alumina oxide composite films have been prepared by alternating current electrodeposition, and their linear optical properties have been systematically characterized by absorption spectra. In the experimental spectra, there exist transverse and longitudinal resonance peaks, which are caused by the surface-plasmon resonance along the diameter and the length of the copper nanorods, respectively. The transverse resonance peak is affected by the diameter and aspect ratio of the nanorod. The longitudinal resonance peak appears at longer wavelength when a polarized light illuminates the film with an angle of incidence of about 70 degrees , where the angle is defined with respect to the surface normal. Moreover, the longitudinal resonance mode is sensitive to the polarization direction when compared with the transverse resonance mode.
The Journal of Chemical Physics 10/2005; 123(9):94710. · 3.33 Impact Factor
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ABSTRACT: BST nanoparticles were directly synthesized from solution at 70 degrees C and then wrapped with zinc doped MgO in solution. This core-shell structure was analyzed by a conjunction of XRD, HRTEM, and FE-SEM. The lattice cell parameter of BST core was found to have shrinkage. The lattice cell mismatch between core and shell creates a variation of lattice cell parameter of BST core and we proposed a new method to estimate it by the XRD peak broadening effect. Two possible modes of matching the BST core and MZO shell were suggested and mode II was assigned to our core-shell structure by the observation of HRTEM and analysis of XRD data. Un-grown BST nanoparticles can also be observed by FE-SEM in fracture grains of the ceramics, which was sintered at 1350 degrees C.
The Journal of Physical Chemistry B 08/2005; 109(29):14006-10. · 3.70 Impact Factor
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ABSTRACT: BST nanoparticles were directly synthesized from solution at 70 °C and then wrapped with zinc doped MgO in solution. This core−shell structure was analyzed by a conjunction of XRD, HRTEM, and FE-SEM. The lattice cell parameter of BST core was found to have shrinkage. The lattice cell mismatch between core and shell creates a variation of lattice cell parameter of BST core and we proposed a new method to estimate it by the XRD peak broadening effect. Two possible modes of matching the BST core and MZO shell were suggested and mode II was assigned to our core−shell structure by the observation of HRTEM and analysis of XRD data. Un-grown BST nanoparticles can also be observed by FE-SEM in fracture grains of the ceramics, which was sintered at 1350 °C.
06/2005;
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ABSTRACT: Microwave dielectric properties of low temperature sintering ZnNb2O6 ceramics doped with CuO-V2O5-Bi2O3 additions were investigated systematically. The co-doping of CuO, V2O5 and Bi2O3 can significantly lower the sintering temperature of ZnNb2O6 ceramics from 1150 to 870C. The secondary phase containing Cu, V, Bi and Zn was observed at grain boundary junctions, and the amount of secondary phase increased with increasing CuO-V2O5-Bi2O3 content. The dielectric properties at microwave frequencies (7–9 GHz) in this system exhibited a significant dependence on the relative density, content of additives and microstructure of the ceramics. The dielectric constant ( r) of ZnNb2O6 ceramics increased from 21.95 to 24.18 with increasing CuO-V2O5-Bi2O3 additions from 1.5 to 4.0 wt%. The quality factors (Q f) of this system decreased with increasing CuO-V2O5-Bi2O3 content and ranged from 36118 to 67100 GHz for sintered ceramics, furthermore, all Q f values of samples with CuO-V2O5-Bi2O3 additions are lower than that of un-doped ZnNb2O6 ceramics sintered at 1150C for 2 h. The temperature coefficient of resonant frequency ( f) changed from –33.16 to –25.96 ppm/C with increasing CuO-V2O5-Bi2O3 from 1.5 to 4.0 wt%
Journal of Electroceramics 12/2004; 14(1):67-74. · 1.19 Impact Factor
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ABSTRACT: Resistance degradation of lead magnesium niobate-based (PMZNT) ceramics during nickel electroplating was investigated using resistivity measurement and auger electron spectroscopy (AES) analysis. It was found that the resistivity of the ceramics remained nearly unchanged at the initial stage of the electroplating, and, as electroplating time increased, the resistivity decreased rapidly. An AES depth profile analysis of a degraded specimen showed oxygen content in the surface to be lower than the theoretical value, and the relationship of oxygen content and detection depth was obtained. The results indicated that Pb2+ and Nb5+ were reduced to lower valence states and oxygen in the lattice was lost, thereby leading to a generation of oxygen vacancies. Hence, the conductivity of the dielectrics was enhanced. The results also indicated that only the outermost surface had suffered the reducing effect induced by hydrogen generated during nickel electroplating, whereas the bulk material remained impervious.
Journal of the American Ceramic Society 12/2004; 85(2):476 - 478. · 2.27 Impact Factor
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ABSTRACT: The effect of silver doping on the DC-voltage resistance failure of lead-based relaxor ferroelectrics was investigated via temperature-humidity-bias (THB) testing, scanning electron microscopy, X-ray diffraction spectroscopy, and electrical measurements. The failure rate of silver-doped specimens was found to increase significantly with the doping level during the THB test. However, some degraded specimens can partially recover their electrical properties after a few days of storing in natural conditions. X-ray diffraction analysis showed that silver could be incorporated into the perovskite lattice in the range of silver contents studied. The presence of an inner-bias field in the degraded ceramics was first demonstrated through hysteresis property measurement. Based on these results, it was inferred that the accumulation of oxygen vacancies under DC-voltage should be responsible for the inner-bias field, which consequently resulted in the increase of electronic defects in the ceramics.
Journal of the American Ceramic Society 12/2004; 86(11):1856 - 1860. · 2.27 Impact Factor
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ABSTRACT: Transparent Ag nanowire arrays embedded in anodic alumina membranes were prepared by a template-based approach combined with ac electrodeposition and subsequent etching of substrate. The optical response of the structure could be attributed to surface plasmon resonance (SPR) of Ag nanowires. When the incident light was perpendicular to the surface of the composite film, only the transverse resonant mode was excited, and a dual peak line shape appeared at about 400 nm in the optical absorption spectrum. The longitudinal resonance mode appeared at a longer wavelength when polarized light illuminated the film with an angle of incidence of about 70°, where the angle was defined with respect to the surface normal. The resonant positions and relative intensities of the two resonant modes were affected by the diameter and aspect ratio of nanowires as well as the polarization direction of incident light. In contrast to the prediction of quasistatic theory, the longitudinal resonance peak did not red shift any more while the aspect ratio was large enough.
10/2004;
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ABSTRACT: We have investigated the structural and magnetic properties of a novel type of hexaferrite with composition of Ba<sub>3</sub>M<sub>2</sub>Fe<sub>23</sub>O<sub>41</sub> (where M=Co and Mn) (Z hexaferrite) with tunable permeability. The material is promising for very high frequency (VHF) control when used in a voltage-controlled oscillator (VCO) as a tunable inductor. We substituted Mn for Co in the composition Ba<sub>3</sub>Co<sub>2-x</sub>Mn<sub>x</sub>Fe<sub>23</sub>O<sub>41</sub> from x=0.0 to 1.2 to improve the inductance tunability and quality factor of the inductor material. Mn substitution had significant influence on the grain size of the sintered hexaferrites, and the coercivity was greatly reduced. The initial permeability and quality factor increased with increasing substitution of Mn for Co until x reached 0.5, an effect attributed to the decrease of the magnetocrystalline anisotropy constant of the hexaferrite and increase of average grain size. The tunability of the samples also increased with increasing Mn substitution, reaching a maximum at x=0.5, and then decreased with further substitution. This behavior is similar to that of the initial permeability and coercivity, and can be explained by the same mechanism.
IEEE Transactions on Magnetics 08/2004; · 1.36 Impact Factor
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ABSTRACT: The increase of silver content in the internal electrodes was found to have a negative influence on accelerated-test life of lead magnesium niobate-based multilayer ceramic capacitors under direct current-voltage. Transmission electron microscopy (TEM) and auger electron spectroscopy (AES) analyses were carried out on the cofired electrode/ceramics interfaces to demonstrate the effect of Ag content in the electrode on the reliability of capacitors. The result showed that Ag could diffuse into the ceramic layers for more than one micrometer. We designed Ag-doping experiments to study the interactions between the ceramics and Ag. Temperature-humidity-bias (THB) tests on Ag-doped disc specimens revealed that the failure rate of the specimens increased with the Ag content in the ceramics. Based on these results, it was inferred that the deterioration of the multilayer ceramic capacitors with the increase of Ag content in the electrodes should be attributed to the Ag diffusion from the electrodes into the oxide ceramics.
Journal of Electroceramics 02/2003; 10(1):57-61. · 1.19 Impact Factor
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ABSTRACT: In the present paper, electrical measurements, air-annealing experiments, and X-ray photoelectron spectroscopy (XPS) were
used to study the lateral growth of nickel coating on the ceramics substrate during electroplating of
hexaferrite multilayer chip inductors (MLCI). It was found that resistivity of the ferrite and inductance of MLCI decreased
continuously during the electroplating. The lateral growth of metal coating occurred only after a certain time of electroplating,
but not immediately. XPS analysis showed that a large part of
on the ferrite surface had been reduced to
during 20 min of nickel electroplating. However, the resistance-degraded specimens can be restored through 2 h of air annealing
at 650°C during which all the
was reoxidized to
Based on the results obtained, it was concluded that
reduction to
induced by hydrogen during electroplating must be responsible for the functional degradation of the ferrite, which then resulted
in the lateral growth of metal coating on the ceramics surface. © 2002 The Electrochemical Society. All rights reserved.
Journal of The Electrochemical Society. 11/2002; 149(12):J89-J92.
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ABSTRACT: Resistive leakage of lead magnesium niobate (PMN) based relaxor ferroelectrics after nickel electroplating was investigated through X-ray photoelectronic spectroscopy (XPS) analysis and annealing experiments in oxygen and argon. It was found that the resistivity of the ceramics declined nonlinearly with the electroplating time. XPS analysis suggested that the reduction of Nb5+ to Nb4+ by hydrogen during electroplating played an important role in the degradation. It was also noted that the degraded specimen can recover its properties completely after oxygen annealing at 600C for 1 hour through the oxidation of Nb4+ to Nb5+. In contrast, almost no oxidization of Nb4+ and improvement of the degradation were observed for the degraded specimen after argon annealing. Therefore, it was concluded that the resistance degradation of the PMN-based relaxor ferroelectrics during electroplating must be ascribed to the oxygen loss and the reduction of Nb5+ to Nb4+.
Journal of Materials Science 07/2002; 37(15):3225-3228. · 2.02 Impact Factor
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ABSTRACT: Resistance measurement, P–E hysteresis measurement, and transmission electron microscope and energy dispersive analysis of x-rays (TEM-EDAX) analysis were used to study the resistance failure of lead magnesium niobate-based multilayer ceramic capacitors (MLCC) under dc voltage. It was found that the failure rate of MLCC with 1/9 Pd/Ag internal electrodes was 10 times that of MLCC with 3/7 Pd/Ag electrodes after the temperature–humidity–bias test (THB). Voltage shifts of hysteresis loops showed that an internal bias field between electrodes of MLCC was formed after THB test. Ag diffusion from electrodes into the ceramics during cofiring was examined through TEM-EDAX analysis. It was also found that the degraded specimens could be partially restored after storing under natural condition. On the basis of these results, the failure mechanism was established that oxygen vacancies induced by Ag diffusion accumulated under the external bias field, which increased the concentration of electronic defects, thereby resulting in the resistance failure of MLCC.
Journal of Materials Research. 03/2002; 17(04):779 - 783.
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ABSTRACT: Resistance degradation of lead magnesium niobate (PMN)-based relaxor ferroelectrics during nickel electroplating, as well
as the recovery of the degraded specimen through air annealing, were investigated by using resistance measurement and X-ray
photoelectron spectroscopy (XPS). It was found that the resistivity of the ceramics declined nonlinearly with the electroplating
time, and eventually, an obvious degradation occurred. The XPS results showed that parts of
and
were reduced to metallic Pb and
by hydrogen during electroplating. In view of defect chemistry, oxygen vacancies and free electrons were produced, leading
to the resistance degradation. It was also found that the degraded PMN-based ceramics could regain its resistivity characteristics
after being annealed in air at high temperatures. The correlation of Pb and
reoxidation and the resistivity recovery was clarified, which in turn confirmed that the generation of metallic Pb and
resulted in the resistance degradation of the ceramics during nickel electroplating. © 2001 The Electrochemical Society.
All rights reserved.
Journal of The Electrochemical Society. 08/2001; 148(9):F180-F183.
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ABSTRACT: The effects of nickel electroplating on electrical properties of PMN-based relaxor ferroelectrics were studied by measuring the resistance and temperature dependence of dielectric constant and dissipation factor. It was found that the insulation resistivity of the specimens declined nonlinearly with electroplating time. Additionally, the dielectric constant and dissipation factor were reduced and enhanced respectively. X-ray photoelectron spectroscopy (XPS) analysis showed that Nb5+ and Pb2+ were partially reduced to Nb4+ and metallic Pb by hydrogen during nickel electroplating, which consequently generated oxygen vacancies and conductive electrons in view of defect chemistry, thereby the conduction was enhanced. On the basis of our experiments, the degradation of electrical properties of PMN-based ferroelectrics was ascribed to resistive leakage resulting from Nb5+ and Pb2+ reductions to lower charge states by hydrogen.
Materials Research Bulletin. 36(12):2103-2109.
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Journal of Solid State Chemistry. 178(1):279-284.
