MgO Nanopowders Research Articles

Sol-gel synthesis and dilute magnetism of nano MgO powder doped with Fe

Mg oxides doped with 1 % 57Fe were prepared by a sol-gel method, and annealed at various temperatures. Nano-size Mg oxides were characterized by Mossbauer spectrometry, magnetization and XRD measurements. The crystalline size of MgO increases with increase of annealing temperature. Samples annealed at 600 °C and 800 °C gave only doublet peaks of paramagnetic Fe3+ in Mossbauer spectra although Fe3+ doping into MgO induced a distorted structure and showed weak ferromagnetism. It is considered that the magnetic property is due to defect induced magnetism by doping Fe3+ into MgO. For a sample heated at 1000 °C, it is found from low temperature Mossbauer spectra that Fe3+ species are located at the core and shell of fine MgFe2O4 grains and diluted in MgO matrix.

Comparative study of the luminescence properties of macro- and nanocrystalline MgO using synchrotron radiation

MgO nano-powder with an average crystallite size of nanoparticles ranging 10–15nm was synthesized using the extractive-pyrolytic method and was studied by room temperature VUV spectroscopy under synchrotron radiation excitation. Comparative analysis of their luminescent properties with that of macrocrystalline powder analogues and an MgO single crystal, grown by the arc-fusion method, has been performed under excitation by pulsed VUV synchrotron radiation. Special attention was paid to VUV spectral range, which is not reachable with commonly used lamp and laser sources. A considerable blue shift of about ∼0.3eV in the excitation spectra of 2.95eV emission band, was revealed in nanocrystalline MgO samples.

Non-Ohmic and dielectric properties of CaCu3Ti4O12-MgO nanocomposites

Graphical abstractDisplay Omitted Highlights? Addition of 5vol.% MgO can improve dielectric and nonlinear properties of CCTO. ? The low-frequency tan? of CCTO-MgO (5vol.%) was greatly reduced. ? e' of CCTO-MgO (5vol.%) is higher than 104 in the frequency range of 102-105Hz. ? Addition of 5vol.% MgO can enhance breakdown voltage and nonlinear coefficient. In this work, CaCu3Ti4O12-xMgO (x=0, 5, and 10vol.%) nanocomposites were prepared by a conventional mixed oxide method using CaCu3Ti4O12 and MgO nanopowders with particles sizes of about 100-300nm and 36-50nm, respectively. The dielectric and electrical properties of CaCu3Ti4O12 and CaCu3Ti4O12/MgO ceramics were investigated. The results revealed that addition of 5vol.% MgO can improve both dielectric and electrical nonlinear properties. The low-frequency loss tangent was greatly reduced; while, the dielectric constant was found to be higher than 104 in the frequency range of 102-105Hz. The decrease in a low-frequency loss tangent is caused by a decrease in DC conductivity. Addition of 5vol.% MgO can also enhance significantly the breakdown voltage and nonlinear coefficient of CaCu3Ti4O12 ceramic. Using impedance spectroscopy analysis, the increase in the breakdown voltage is attributed to an increase in the resistance of grain boundaries.

Effect of Magnesia on Zinc Oxide Stabilized Nano Alumina Ceramic Powder in Sintering Process and its Impact on Mechanical Properties

In Present work, the properties of Al2O3 powder was studied through incorporation of MgO Nano powder along with ZnO Nano powder and followed by sintering at various temperatures. Previously ZnO and MgO were introduced with Al2O3 separately to improve physical and mechanical properties like densification, micro hardness, fracture toughness etc. In current project, 0.25wt% and 0.50wt% MgO was added with β- Al2O3 matrix along with constant 0.1wt% ZnO and sintered those samples at 14500°C, 15000°C, 15500°C respectively. Properties like densification, micro hardness, and wear rate of all these sintered products were measured and discussed where the best composition found was 0.1% ZnO-0.25%MgO-99.65% Al2O3 sintered at 15000°C. Change in properties was observed due to faster densification rate and pinning effect provided by the doping particles.

Electrical Transport Properties of (Bi1.6Pb0.4Sr2Ca2Cu3O10)/Ag Tapes with Different Nanosized MgO

MgO nanopowders with average size 20 and 40 nm were introduced into (Bi1.6Pb0.4Sr2Ca2Cu3O10)(MgO)x(x=0–0.15 wt.%) in the pellet form. The optimum amounts for the highest transport critical current densityJcwerex=0.10and 0.01 wt.% for 20 and 40 nm MgO, respectively. These results were used to fabricate MgO added (Bi, Pb)-2223/Ag sheathed tapes using the powder-in-tube method. The tapes were sintered at 845°C for 50 h and 100 h. The structure, microstructure, andJcof the tapes were determined. The temperature and magnetic field dependence ofJcfor the MgO added tapes exhibited a significant enhancement compared with the nonadded tapes.Jcof 20 nm MgO added tape was higher compared with the 40 nm MgO added tape. A higherJcwas obtained when the tapes were sintered for 100 h. The increase inJccan be explained as the increase of the flux pinning strength by nanosized MgO. The nanoparticle with size closer to the coherence length was more effective in enhancingJc.

Magnesia nanoparticles in liquid electrolyte for dye sensitized solar cells: An effective recombination suppressant?

Recombination reactions at the photoanode/electrolyte interface reduce the photovoltaic conversion efficiency of dye sensitized solar cells (DSSCs). Unlike modification of titania photoanode by coating with MgO which act as a barrier layer toward recombination, addition of MgO nanopowder to electrolyte prevents recombination through adsorption of anions (triiodide/iodide) from electrolyte. In the present study, the surface charge of MgO has been utilized to adsorb anions from electrolyte. This anionic adsorption onto the MgO nanopowders in electrolyte has been confirmed by zeta potential measurements. MgO retards the recombination reaction as efficiently as 4-tert-butylpyridine (TBP) which is the most widely used additive in the electrolyte. Higher photocurrent and conversion efficiency is achieved by using MgO loaded electrolyte as compared to TBP added electrolyte. Dark current measurements show that recombination reactions are effectively retarded by use of MgO loaded electrolytes. Open circuit voltage decay measurements also confirm higher electron lifetime at the titania/electrolyte interface in MgO loaded electrolyte based cell as compared to additive free electrolyte based cell.

Exciton Formation at Solid–Solid Interfaces: A Systematic Experimental and ab Initio Study on Compressed MgO Nanopowders

An important and so far neglected class of structural elements affecting the overall properties of metal oxide nanopowders are interfaces between individual nanocrystals. In this work, we show experimentally that these defects inside a powder of compressed MgO nanocubes are subject to photoexcitation in the UV light range. In particular, we identify a so far unobserved photoluminescence emission process at 2.5 eV. First-principles calculations of the optical properties of nanocrystal interfaces provide plausible candidates for both light absorbing and emitting sites, which involve different types of interface features. It was found that edge dislocations that arise from interfaces between nanocube edges and terraces induce a significant electrostatic perturbation of the interfacial electronic states. This leads to exciton generation and luminescence at even lower energies than those related to corners and edges of MgO nanocubes.

Synthesis and Characterization of Highly Crystalline MgO Nanopowders via a Modified Chemical-Precipitation Process

A modified chemical-precipitation method is proposed to synthesize MgO nanopowders with high crystallinity at a low temperature of 400 degrees C using acetic acid as a modifier. The as-obtained intermediates and final products were investigated by Fourier-transformed infrared spectroscopy, thermogravimetric analysis, X-ray diffraction and transmission electron microscopy, respectively. The influence of acetic acid in the MgO preparation process was also investigated by a comparison of the samples without acetic acid, and the mechanism of acetic acid modification is also proposed. The carboxyl group of acetic acid could coordinate with Mg atom in a monodentate mode to form a new organic ligand intermediate Mg(OH)(OCOCH3), which facilitates the thermal decomposition of the intermediate at low temperature and enhances the crystallization of MgO.

Characterization of the MgO Nano Powder Synthesized by Using a Liquid Phase Precursor Method for Plasma Display Panels Protecting Layer

The characterization of MgO nano powders that were synthesized using a conventional firing liquid phase precursor, rapid firing liquid phase precursor and rapid cooling firing liquid phase precursor were investigated as a function of the heating and cooling rates and the concentration of the impregnated Mg(NO3)2 x 6H2O solution from 1 to 20%. The relative intensity of diffraction peak in the MgO nano powder increased with increasing firing temperature from 800 to 1200 degrees C, indicating a higher crystalline MgO nano powder. In addition, the relative intensities of the MgO nano powder synthesized at the designated temperature showed similar behavior regardless of the impregnated Mg(NO3)2 x 6H2O solution concentration from the XRD analysis. The field emission scanning electron microscope and high resolution transmission electron microscope analysis showed that the size and shape of the MgO nano powder can be controlled by the temperature, the firing and cooling processes, and the impregnated Mg(NO3)2 x 6H2O solution concentration. Moreover, the CL spectra of the synthesized MgO nano powders showed a higher luminance efficiency than commercial MgO nano powder.

Correlation between ferromagnetism and defects in MgO nanocrystals studied by positron annihilation

High purity MgO nanopowders were pressed into pellets and annealed in air from 100 to 1400°C. Variation of the microstructures was investigated by X-ray diffraction and positron annihilation spectroscopy. Annealing induces an increase in the MgO grain size from 27 to 60nm with temperature increasing up to 1400°C. Positron annihilation measurements reveal vacancy defects including Mg vacancies, vacancy clusters, microvoids and large pores in the grain boundary region. Rapid recovery of Mg monovacancies and vacancy clusters was observed after annealing above 1200°C. Room temperature ferromagnetism was observed for MgO nanocrystals annealed at 100, 700, and 1000°C. However, after 1400°C annealing, MgO nanocrystals turn into diamagnetic. Our results suggest that the room temperature ferromagnetism in MgO nanocrystals might originate from the interfacial defects.

Theoretical Analysis of the FTIR Absorption Characteristic of Nano-Powder

The infrared absorption behaviors of nano-MgO with different sizes have been investigated based on XRD and IR data. The blue shifts of infrared absorption peaks with the decrease of the particles size have been analyzed by constructing one-dimensional vibration model. Adopting the quantum physics analyzed method, we provide the reasonable explanations for the red shifts of infrared absorption peaks as the average particle size of nano-MgO powder is down to less than 50 nm.

Theoretical Analysis of the FTIR Absorption Characteristic of Nano-Powder

The infrared absorption behaviors of nano-MgO with different sizes have been investigated based on XRD and IR data. The blue shifts of infrared absorption peaks with the decrease of the particles size have been analyzed by constructing one-dimensional vibration model. Adopting the quantum physics analyzed method, we provide the reasonable explanations for the red shifts of infrared absorption peaks as the average particle size of nano-MgO powder is down to less than 50 nm.

Preparation of iron oxide nanoparticles supported on magnesium oxide for producing high-quality single-walled carbon nanotubes

Fe 3O 4 nanoparticles with a narrow diameter distribution having an average diameter of 10.33 nm ± 2.99 nm (average diameter ± standard deviation) were prepared by a precipitation method. The Fe 3O 4 nanoparticles were supported on MgO by mixing the MgO nanopowder with the required amount of Fe 3O 4 nanoparticles in water under extensive sonication. Single-walled carbon nanotubes (SWCNTs) were synthesized by the chemical vapor deposition (CVD) of methane over the Fe 3O 4/MgO catalyst. Transmission electron microscopy showed that a large number of SWCNT bundles of nearly uniform diameter were produced by the CVD method. The average diameter of the produced SWCNTs was ca. 1.22 nm. Thermogravimetric analysis showed that the weight loss was approximately 19% by oxidation of carbon in the temperature range of 400–680 °C. The ratio of the intensity of the D-band to the G-band was 0.03, indicating that the SWCNTs were well-graphitized.

Optical Properties of Nanocrystal Interfaces in Compressed MgO Nanopowders

The optical properties and charge trapping phenomena observed on oxide nanocrystal ensembles can be strongly influenced by the presence of nanocrystal interfaces. MgO powders represent a convenient system to study these effects due to the well-defined shape and controllable size distributions of MgO nanocrystals. The spectroscopic properties of nanocrystal interfaces are investigated by monitoring the dependence of absorption characteristics on the concentration of the interfaces in the nanopowders. The presence of interfaces is found to affect the absorption spectra of nanopowders more significantly than changing the size of the constituent nanocrystals and, thus, leading to the variation of the relative abundance of light-absorbing surface structures. We find a strong absorption band in the 4.0−5.5 eV energy range, which was previously attributed to surface features of individual nanocrystals, such as corners and edges. These findings are supported by complementary first-principles calculations. The possibility to directly address such interfaces by tuning the energy of excitation may provide new means for functionalization and chemical activation of nanostructures and can help improve performance and reliability for many nanopowder applications.

Chirality-enriched semiconducting carbon nanotubes synthesized on high surface area MgO-supported catalyst

Single-walled carbon nanotubes (SWCNTs) with a narrow diameter distribution were synthesized by radio frequency-Catalytic Chemical Vapor Deposition (RF-CCVD) through the pyrolysis of CH4. Fe–Co bimetallic catalytic nanoclusters were supported on high-surface area MgO nanopowders and used in the nanotube synthesis process. Nanolog absorption fluorescence analysis was used to characterize the chiralities of the as-produced SWCNTs over this nanostructural catalyst. In the final SWCNT sample, the (7,5) semiconducting carbon nanotube species were found to be dominant, with a low chirality variation.

Mechanism Analysis of FTIR Absorption Characteristic of MgO Nano-Powder

Nano-MgO powders with different size form 30 to 100 nm are prepared and measured by XRD and IR. FTIR results show that nano-MgO powder has abnormal infrared absorption behaviors compared with that of micron scale; and there exist blue shifts of infrared absorption peaks with the decrease of the particles size. But when the average particle size of nano-MgO powder is down to less than 50 nm, there are red shifts of infrared absorption peaks. The aim of the paper is to analyze the mechanism of IR absorption characteristic of MgO Nano-powder by a single- dimensional chain vibration model.

Discharge Characteristics of MgO Nano-Powdered Functional Layer in AC-PDP

We have studied discharge characteristics of MgO nano-powdered functional layer in accordance with their particle sizes in AC-PDP. The MgO nano-powder's size was controlled and confirmed that the different particle sizes were distributed according to the sintering times throughout the particle size analyzer (PSA) measurement. We made the different 6 inch test panels, in which the different particle size's functional layers were applied, for measurements of the firing voltage, secondary electron emission coefficient and cathodoluminescence (CL) spectrum. It is shown that the functional layer makes the firing voltage and sustain voltage low, and the particles with large size have the lowest firing voltage and sustain voltage, which are related to the high secondary electron emission coefficient.

The effects of high purity MgO nano-powders on the electrical properties of AC-PDPs

A major goal in plasma display panel technology is to reduce power consumption and increase efficiency. A candidate method to accomplish this goal is to increase the Xe content in discharge gases. However, this method has the weak point of increasing discharge voltages. High purity MgO powders made by the self-reaction method are adopted to overcome this disadvantage. From scanning electron microscope analysis, particles of the powders were observed to have very sharp edges, and the impurity content is very low according to inductively-coupled plasma mass spectrometry analysis. Moreover, the powders show a very high photo-induced electron emission and exo-electron emission, and have a very low concentration of oxygen vacancies by cathodoluminescence. Finally, the discharge voltage of high purity MgO powder-adopted films is reduced by about 34% compared to that of conventional films.

Effects of Mg-Doping on Structure and Electric Properties of Mg<sub>x</sub>Zn<sub>1-x</sub>O:Al Ceramics

MgxZn1-xO:Al ceramics with low resistivity using ZnO, MgO and Al2O3 nano-powders as raw materials were obtained by unpressurized sintering. The influence of Mg content on structure and electric properties of MgxZn1-xO:Al ceramics were studied. The results indicate that there is a single phase of wurtzite structure of ZnO in MgxZn1-xO:Al ceramics at x ≤ 0.3, and when the value of x was 0.3, phase separation was observed. The grains become smaller and more homogeneous with increasing Mg content to above 0.3. The resistivity of MgxZn1-xO:Al ceramics obviously increases with increasing Mg concentration due to the decrease of the carrier concentration and the mobility deriving from the decrease of Al-doping efficiency. The electrical conduction of MgxZn1-xO:Al ceramics can be markedly improved by increasing the Al-doping level and the lowest resistivity of 8.3×10-4Ω•cm can be obtained when Mg/(Mg+Zn)=0.2 and Al/(Mg+Zn+Al)=0.03.

Cubic-Shaped Nano-MgO Powder and its Infrared Absorption Properties

A precipitation-pyrolysis process was used for the synthesis of cubic nano-MgO powder. The main effect factors on the size and shape of nano-MgO powder such as mechanical stirring rate, organic reagent, and calcinations of the process were investigated. XRD and TEM were used to study on composition, morphology and size of nano-MgO powder. The results indicate that at the condition of mechanical stirring rate 510 rmp, glycol as organic crystal controller, calcination time 3 h, cubic nano-MgO powder was prepared with average size of 35 nm. FTIR results show that cubic nano-MgO powder has abnormal infrared absorption behaviors compared with that of micron scale.