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1.
S. PatraS.K. Pradhan 《Acta Materialia》2012,60(1):131-138
ZnTe quantum dots (QD) have been synthesized in a quick single-step process by mechanically alloying a stoichiometric mixture of elemental Zn and Te powders at room temperature under Ar with 1 h of milling. The detailed microstructure of these powdered QD has been characterized by both Rietveld analysis of X-ray powder diffraction data and high resolution transmission electron microscopy. The results reveal that almost monodispersed spherical QD of ∼5 nm size were synthesized after 15 h of milling. These QD all belong to the cubic (Zn blende) phase and contain different kinds of stacking faults but with low lattice strain. The UV-vis absorbance spectra of ZnTe QD depict a significant blue shift with decreasing size of QD and the band gap estimated taken from the sharp absorbance peak position is greater than that of the bulk counterpart. The band gap increases with increasing milling time up to 15 h with a continuous decrease in the size of these QD and, therefore, their optical properties can be fine tuned by varying the milling time. 相似文献
2.
Guoping Dong Botao WuFangteng Zhang Liaolin ZhangMingying Peng Dongdan ChenE. Wu Jianrong Qiu 《Journal of Alloys and Compounds》2011,509(38):9335-9339
Silicate glasses containing PbS quantum dots (QDs) with narrow size distribution were prepared through heat treatment. Transmission electron microscopy (TEM) results show that spherical PbS QDs are densely dispersed in the glassy matrix. Using ZnS-PbO to replace PbS as precursor of PbS QDs, the size distribution of PbS QDs in glasses becomes more uniform. Tunable infrared luminescence from 1100 to 2200 nm has been obtained by controlling the glassy matrix and preparation parameters. Obvious optical amplification at communication windows of 1.55 μm and 1.33 μm is probed, and the PbS QDs doped glasses using ZnS-PbO as precursor exhibit larger optical amplification. The PbS QDs doped glasses with intense optical amplification are considered to be promising candidate as gain medium for broadband fiber amplifier and tunable fiber laser. 相似文献
3.
S. SainS.K. Pradhan 《Journal of Alloys and Compounds》2011,509(10):4176-4184
(Cd0.8Zn0.2)S quantum dots with a mixture of both cubic (Zinc-blende) and hexagonal (Wurtzite) phases have been prepared within 75 min by mechanical alloying the stoichiometric mixture of Cd, Zn and S powders at room temperature in a planetary ball mill under Ar. The Rietveld analysis of X-ray powder diffraction data reveals relative phase abundances of both cubic and hexagonal phases and several microstructure parameters like lattice parameters, particle sizes, lattice strains, concentrations of different kinds of stacking faults, etc. in both the phases. At the time of formation, hexagonal phase dominates over the cubic phase (molar ratio ∼0.6:0.4), but in course of milling up to 15 h, the hexagonal phase partially transforms to cubic phase and the molar ratio becomes ∼0.4:0.6. Particle sizes of hexagonal and cubic phases reduce to ∼4.5 nm and 12.5 nm, respectively, after 15 h of milling. The hexagonal phase contains a significant amount of lattice strain in comparison to cubic phase. The presence of different kinds of stacking faults is revealed clearly from the high resolution transmission electron microscope (HRTEM) images. 相似文献
4.
Optical and Raman scattering studies on SnS nanoparticles 总被引:1,自引:0,他引:1
S. SohilaM. Rajalakshmi Chanchal GhoshA.K. Arora C. Muthamizhchelvan 《Journal of Alloys and Compounds》2011,509(19):5843-5847
Tin sulfide nanoparticles were synthesized through wet chemical route. Structure and phase purity were confirmed by powder XRD. Morphology and size were identified from TEM and AFM. The room temperature photoluminescence spectrum shows the band edge emission at 1.57 eV. The direct and indirect band gaps are estimated from UV-vis-NIR absorption spectrum as 1.78 and 1.2 eV, respectively. Blue shift of 0.48 eV observed for direct transition and 0.2 eV for indirect transition as compared to bulk band gap is due to quantum confinement effect. The Raman spectrum of SnS nanoparticles shows all the predicted Raman modes which show shift towards lower wave number side in comparison with those of the SnS single crystal. This is attributed to phonon confinement. 相似文献
5.
F.Y. ShenWenxiu Que X.T. YinY.W. Huang Q.Y. Jia 《Journal of Alloys and Compounds》2011,509(37):9105-9110
Colloidal zinc sulfide (ZnS) quantum dots are synthesized by a solvothermal route from Zn(Ac)2·2H2O, sulfur powder and oleylamine at 120-240 °C. Microstructural, morphological, and optical properties of the as-synthesized ZnS quantum dots are characterized by X-ray diffraction analysis, transmission electron microscopy, UV-vis absorption spectroscopy, and photoluminescence spectroscopy. Results indicate that the obtained ZnS quantum dots distribute uniformly, the particle size is in the range between 1.7 nm and 3.1 nm, and the band gap decreases from 4.16 eV to 3.90 eV with an increase of the particle size. The size-dependent photoluminescence exhibits a strongly broadened peak accompanied by a pronounced blue-shift. It is also found that the size of the ZnS nanocrystals can be effectively controlled by adjusting synthesis temperature. It is shown that the present method is also applicable to synthesize other binary II-VI semiconductor materials, such as ZnSe quantum dots. 相似文献
6.
Lili Yang Jinghai Yang Xiaoyan Liu Yongjun Zhang Yaxin Wang Hougang Fan Dandan Wang Jihui Lang 《Journal of Alloys and Compounds》2008,463(1-2):92-95
ZnO quantum dots (QDs) were fabricated at low temperature of 200 °C through thermal decomposition method with slight introduction of sodium dodecyl sulfate (SDS). The morphology, structure and optical properties were investigated by the methods of X-ray diffraction (XRD), transmission electron microscope (TEM), photoluminescence (PL) and Raman spectrum, respectively. The XRD results showed the as-synthesized ZnO QDs had hexagonal wurtzite structure and the average grain size estimated from Scherrer formula was 7.5 nm which had a good agreement with TEM result. And it is evident that the introduction of SDS can actually decrease the grain size to form ZnO QDs. The Raman results also indicated that the ZnO QDs keep the overall crystal structure of the bulk ZnO. Both spatial confinement within the dot boundaries and phonon localization by defects were the mainly reason for the only few cm−1 redshift of the Raman scatter peaks. The room-temperature photoluminescence reveals that the as-prepared ZnO QDs exhibit an ultraviolet emission at 380 nm and a broad deep level emission band in the range of 420–700 nm in wavelength, which testified the Raman and XRD results that the as-synthesized ZnO QDs had defects. Moreover, the growth mechanism of ZnO QDs was also discussed in the article. 相似文献
7.
R. Sakthi Sudar Saravanan D. PukazhselvanC.K. Mahadevan 《Journal of Alloys and Compounds》2011,509(10):4065-4072
Zn(1−x)CdxS and Zn(1−x)CdxS:Mn2+ semiconductor quantum dots (2-4 nm) have been prepared by a novel solvothermal route assisted microwave heating method. The growth parameters governing the smaller size and higher yield have been optimized. The synthesized QDs exhibit a significant blue shift as compared to their corresponding bulk counterpart in the UV-vis optical absorption spectrum. The dielectric constant value varies from 2.79 to 6.17 (at 40 °C, 1 kHz) depending upon the composition of the alloy; lower value corresponds to Zn0.75Cd0.25S:Mn2+ and the higher value corresponds to Zn0.25Cd0.75S:Mn2+. The crystallite size to exciton bohr radius ratio being <1 indicates a strong quantum confinement effect in both CdS and ZnS QDs. The quantum confinement effect exists in the sequence of ZnS:Mn2+ < Zn(1−x)CdxS:Mn2+ (x < 0.5) < ZnS < Zn(1−x)CdxS < CdS < CdS:Mn2+. 相似文献
8.
In this work, four different volume fractions of Al2O3 (10, 20, 30 and 40 vol.%) were mixed with the fine Al powder and the powder blends were milled for 5 h. Scanning electron microscopy analysis, particle size analysis and bulk density measurements were used to investigate the morphological changes and achieving the steady state conditions. The results showed that increasing the Al2O3 content can provide the steady state particle size in 5 h milling process. It was found that increasing the volume fraction of Al2O3 leads to increasing the uniformity of Al2O3. Standard deviations of microhardness measurements confirmed this result. The XRD pattern and XRF investigations depicted that increasing the Al2O3 content causes an increase in the crystal defects, micro-strain and Fe contamination during 5 h milling process of nanocrystalline composite powders while the grain size is decreased. To investigate the effect of milling time, Al-30 vol.% Al2O3 (which achieved steady state during 5 h milling process) was milled for 1-4 h. The results depicted that the milling time lower than 5 h, do not achieve to steady state conditions. 相似文献
9.
T.F. Marinca I. Chicina? O. IsnardV. Pop F. Popa 《Journal of Alloys and Compounds》2011,509(30):7931-7936
Nanocrystalline nickel ferrite (NiFe2O4) has been synthesized from a stoichiometric mixture of oxides NiO and α-Fe2O3 in a high energy planetary mill. An annealing at 350 °C, after milling, was used to improve the solid state reaction. The obtained powders were investigated by X-ray diffraction, magnetic measurements, scanning electron microscopy, X-ray microanalysis and differential scanning calorimetry. The particles size distribution was analyzed using a laser particle size analyser. The nickel ferrite begins to form after 4 h of milling and continuously form up to 16 h of milling. The obtained nickel ferrite has many inhomogeneities and a distorted spinel structure. The mean crystallites size at the final time of milling is 9 ± 2 nm and the lattice parameter increases with increase the milling time. DSC measurements revealed a large exothermic peak associated with cations reordering in the crystalline structure. The magnetization of the obtained powder depends on the milling time and annealing. After the complete reaction between the starting oxides the milling reduces the magnetization of the samples. The magnetization increases after annealing, due to the reorganization of the cations into the spinel structure. 相似文献
10.
Single nanocrystalline ZnWO4 powders were successfully synthesized by ball milling at room temperature. A stoichiometric mixture of ZnO and WO3 in a 1:1 molar ratio was subjected to intense mechanical treatment in air using a planetary ball mill (Fritsch - Premium line - Pulversette No. 7) for a period varying from 5 to 300 min. The influence of the four different milling conditions was investigated on the formation of ZnWO4. The products obtained were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer-Emmer-Teller (BET) surface area, infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The synthesis of ZnWO4 powder started after 5 min milling time and finished after 30 min milling time at a higher speed (1000 rpm). The mechanical treatment up to 300 min did not lead to phase and structure change of ZnWO4. The product obtained contained nanoparticles with a size of about 50 nm. The photocatalytic activity of the ZnWO4 powders obtained was investigated by degradation of a model aqueous solution of Malachite Green (MG) upon UV-light irradiation. 相似文献
11.
B. Tian F. ChenY.X. Tong L. LiY.F. Zheng Y. Liu Q.Z. Li 《Journal of Alloys and Compounds》2011,509(13):4563-4568
This study investigated the phase transformation of the flaky shaped Ni-Mn-Ga powder particles with thickness around 1 μm prepared by vibration ball milling and post-annealing. The SEM, XRD, DSC and ac magnetic susceptibility measurement techniques were used to characterize the Ni-Mn-Ga powders. The structural transition of Heusler → disordered fcc occurred in the powders prepared by vibration ball milling (high milling energy) for 4 h, which was different from the structural transition of Heusler → disordered fct of the powders fabricated by planetary ball milling (low milling energy) for 4 h. The two different structures after ball milling should be due to the larger lattice distortion occurred in the vibration ball milling process than in the planetary ball milling process. The structural transition of disordered fcc → disordered bcc took place at ∼320 °C during heating the as-milled Ni-Mn-Ga powders, which was attributed to the elimination of lattice distortion caused by ball milling. The activation energy for this transition was 209 ± 8 kJ/mol. The Ni-Mn-Ga powder annealed at 800 °C mainly contained Heusler austenite phase at room temperature and showed a low volume of martensitic transformation upon cooling. The inhibition of martensitic transformation might be attributed to the reduction of grain size in the annealed Ni-Mn-Ga particles. 相似文献
12.
Ali Hussain Reshak I.V. KitykR. Khenata S. Auluck 《Journal of Alloys and Compounds》2011,509(24):6737-6750
An all electron full potential linearized augmented plane wave method, within a framework of GGA (EV-GGA) approach, has been used for an ab initio theoretical study of the effect of increasing tellurium content on the band structure, density of states, and the spectral features of the linear and nonlinear optical susceptibilities of the cadmium-selenide-telluride ternary alloys CdSe1−xTex (x = 0.0, 0.25, 0.5, 0.75 and 1.0). Our calculations show that increasing Te content leads to a decrease in the energy band gap. We find that the band gaps are 0.95 (1.76), 0.89 (1.65), 0.83 (1.56), 0.79 (1.44) and 0.76 (1.31) eV for x = 0.0, 0.25, 0.5, 0.75 and 1.0 in the cubic structure. As these alloys are known to have a wurtzite structure for x less than 0.25, the energy gaps are 0.8 (1.6) eV and 0.7 (1.55) eV for the wurtzite structure (x = 0.0, 0.25) for the GGA (EV-GGA) exchange correlation potentials. This reduction in the energy gaps enhances the functionality of the CdSe1−xTex alloys, at least for these concentrations, leading to an increase in the effective second-order susceptibility coefficients from 16.75 pm/V (CdSe) to 18.85 pm/V (CdSe0.75Te0.25), 27.23 pm/V (CdSe0.5Te0.5), 32.25 pm/V (CdSe0.25Te0.75), and 37.70 pm/V (CdTe) for the cubic structure and from 12.65 pm/V (CdSe) to 21.11 pm/V (CdSe0.75Te0.25) in the wurtzite structure. We find a nonlinear relationship between the absorption/emission energies and composition, and a significant enhancement of the electronic properties as a function of tellurium concentration. This variation will help in designing better second-order susceptibility materials by manipulating of the electronic structures of these materials with different compositions to achieve more delocalized atomic bonds. 相似文献
13.
X.Q. OuM. Song T.T. ShenD.H. Xiao Y.H. He 《International Journal of Refractory Metals and Hard Materials》2011,29(2):260-267
The ultrafine grained WC-10Co-0.45Cr3C2-0.25VC alloys were fabricated through planetary ball milling and low pressure sintering. The effects of the cobalt particle size, milling speed and sintering temperature on the microstructure, hardness and fracture toughness of the ultrafine grained alloys were investigated using optical microscopy, scanning electron microscopy and mechanical testing. The results showed that the mechanical properties of the low pressure-sintered alloys substantially depend on the milling speed and sintering temperature. At the same time, the hardness and fracture toughness of the samples can be increased from 1703 MPa and 8.90 MN m−3/2 to 1789 MPa and 11.21 MN m−3/2, respectively, when the cobalt particle size is reduced from 17 μm to 1.4 μm. 相似文献
14.
All spray pyrolysis deposited CdS sensitized ZnO films for quantum dot-sensitized solar cells 总被引:1,自引:0,他引:1
Guang ZhuTian Lv Likun Pan Zhuo SunChangqing Sun 《Journal of Alloys and Compounds》2011,509(2):362-365
Sensitized-type solar cells based on ZnO photoanode and CdS quantum dots (QDs) as sensitizers have been fabricated. Both ZnO films and CdS QDs are prepared using ultrasonic spray pyrolysis (USP) deposition technique. This method allows a facile and rapid deposition and integration between CdS QDs and ZnO films without the need for post thermal treatment. The photovoltaic performances of the cells are investigated. The results show that the performance of the cell based on all USP deposited CdS sensitized ZnO photoanode achieves maximally a short circuit current density of 6.99 mA cm−2 and a power conversion efficiency of 1.54%. 相似文献
15.
Cu-Zr alloys have many applications in electrical and welding industries for their high strength and high electrical and thermal conductivities. These alloys are among age-hardenable alloys with capability of having nano-structure with high solute contents obtainable by the mechanical alloying process. In the present work, Cu-Zr alloys have been developed by the mechanical alloying process. Pure copper powders with different amounts of 1, 3 and 6 wt% of commercial pure zirconium powders were mixed. The powder mixtures were milled in a planetary ball mill for different milling times of 4, 12, 48 and 96 h. Ball mill velocity was 250 rpm and ball to powder weight ratio was 10:1. Ethanol was used as process control agent (PCA). The milling atmosphere was protected by argon gas to prevent the oxidation of powders. The milled powders were analysed by XRD technique and were also investigated by SEM observations. Lattice parameters, crystal sizes and internal strains were calculated using XRD data and Williamson-Hall equation. Results showed that the lattice parameter of copper increased with increasing milling time. The microstructure of milled powder particles became finer at longer milling time towards nano-scale structure. SEM observations showed that powder particles took plate-like shapes. Their average size increased initially and reached a maximum value then it decreased at longer milling times. Different zirconium contents had interesting effects on the behavior of powder mixtures during milling. 相似文献
16.
Nanocrystal formation of SnO2 in xSnO2-(100 − x)MgO (x in mol.%) nanocrystalline composite thin films is reported. SnO2 and MgO exhibit strong immiscibility behavior below 750 °C, leading to controllable particle size of SnO2 in the MgO matrix by changing their composition. The particle size of SnO2 can also be controlled by increasing the annealing temperature. Above 750 °C MgO and SnO2 react to yield a MgO-Mg2SnO4-SnO2 composite in which the size of the SnO2 nanophase increases with increasing temperature. By controlled choice of the composition and annealing conditions the band gap of SnO2 can be continuously increased from 3.89 to 4.5 eV. We discuss this behavior in terms of the quantum confinement effect. The method provides a generic approach to tuning the band gap in nanocomposite systems over a wide energy range. 相似文献
17.
J. Safari G.H. Akbari A. ShahbazkhanM. Delshad Chermahini 《Journal of Alloys and Compounds》2011,509(39):9419-9424
The effect of milling time on the microstructure and mechanical properties of Al and Al-10 wt.% Mg matrix nanocomposites reinforced with 5 wt.% Al2O3 during mechanical alloying was investigated. Steady-state situation was occurred in Al-10Mg/5Al2O3 nanocomposite after 20 h, due to solution of Mg into Al matrix, while the situation was not observed in Al/5Al2O3 nanocomposite at the same time. For the binary Al-Mg matrix, after 10 h, the predominant phase was an Al-Mg solid solution with an average crystallite size 34 nm. Up to 10 h, the lattice strain increased to about 0.4 and 0.66% for Al and Al-Mg matrix, respectively. The increasing of lattice parameter due to dissolution of Mg atom into Al lattice during milling was significant. By milling for 10 h the dramatic increase in microhardness (155 HV) for Al-Mg matrix nanocomposite was caused by grain refinement and solid solution formation. From 10 to 20 h, slower rate of increasing in microhardness may be attributed to the completion of alloying process, and dynamic and static recovery of powders. 相似文献
18.
Four different methods, i.e. hydriding combustion synthesis + mechanical milling (HCS + MM), induction melting (followed by hydriding) + mechanical milling (IM(Hyd) + MM), combustion synthesis + mechanical milling (CS + MM) and induction melting + mechanical milling (IM + MM), were used to prepare Mg2Ni-based hydrogen storage alloys used as the negative electrode material in a nickel-metal hydride (Ni/MH) battery. The structural and electrochemical hydrogen storage properties of the Mg2Ni-based alloys have been investigated systematically. The XRD results indicate that the as-milled products show nanocrystalline or amorphous-like structures. Electrochemical measurements show that the as-milled hydrides exhibit higher discharge capacity and better electrochemical kinetic property than the as-milled alloys. Among the four different methods, the HCS + MM product possesses the highest discharge capacity (578 mAh g−1), the best high rate dischargeability (HRD) and the highest exchange current density (58.8 mA g−1). It is suggested that the novel method of HCS + MM is promising to prepare Mg-based hydrogen storage electrode alloy with high discharge capacity and activity. 相似文献
19.
I. Ozdemir S. MuecklichH. Podlesak B. Wielage 《Journal of Materials Processing Technology》2011,211(7):1260-1267
A comparative evaluation has been carried out on the microstructure of aluminum based SiC and Al2O3 particle reinforced composites produced by semi-solid direct squeeze forming of composite powder at temperatures of 635-645 °C. The study is focused on the distribution of the reinforcement and the intermetallic phases, the porosity content, the microstructure of the matrix phase, the interfacial state and mechanical properties. The particle size of the reinforcements, the time of the high-energy ball milling procedure for the fabrication of composite powder and the semi-solid forming temperature had a strong influence on the quality of sample in terms of distribution of reinforcement and interfacial interaction. Ball milling improves the interface formation between reinforcement and matrix and influences the remelting behaviour. Increasing ball milling time and decreasing semi-solid forming temperature with isothermal holding time resulted in relatively homogenous microstructures and in a reduced amount of interaction between SiC and metal matrix. Best results were obtained for 5 vol.% SiCp composites after 3 h ball milling, semi-solid formed at 635 °C and held for 10 min. 相似文献
20.
Nanocrystalline stoichiometric Ti0.9Al0.1N powder has been prepared by ball-milling the α-Ti (hcp) and aluminum (fcc) powders under N2 at room temperature. Initially, α-Ti phase partially transformed to the transient cubic β-Ti phase and Ti0.9Al0.1N (fcc) phase is noticed to form after 3 h of milling. Nanocrystalline stoichiometric Ti0.9Al0.1N phase is formed after 7 h of milling. After 1 h of milling, all Al atoms are diffused into the α-Ti matrix. The transient β-Ti phase is noticed to form after 1 h of milling and disappears completely after 7 h of milling. Microstructure characterization of unmilled and ball-milled powders by analyzing XRD patterns employing the Rietveld structure refinement reveals the inclusion of Al and nitrogen atoms into the Ti lattice on the way to formation of Ti0.9Al0.1N phase. Microstructure of ball-milled samples is also characterized by HRTEM. The particle size of Ti0.9Al0.1N phase, as obtained from XRD method, is ∼5 nm which is very close to that obtained from HRTEM. 相似文献