Doped Zinc Oxide Powders Research Articles

LOW TEMPERATURE COMBUSTION SYNTHESIS AND CHARACTERIZATION OF UNDOPED AND SAMARIUM DOPED ZINC OXIDE NANOPARTICLES

Zinc oxide (ZnO) and samarium (Sm) doped ZnO nanoparticles (NPs) were synthesised by solution combustion approach using citric acid as fuel. The formation of hexagonal wurtzite structure of pure and Sm doped ZnO powder was prepared and confirmed by x-ray diffraction (XRD). The structure formation, morphological and elemental analysis of pure and Sm doped ZnO powder were analysed using XRD, Raman spectra, scanning electron microscopy (SEM) and xray fluorescence spectroscopy (XRF). The results indicated that the trivalent Sm ions were successfully doped in to the lattice of ZnO matrix. The XRD images showed that both ZnO and Sm doped ZnO NPs are highly crystalline, having hexagonal wurtzite structure.

Fabrication and ethanol sensing of sol–gel grown zinc oxide powder: the effect of cobalt and copper doping

Pure, cobalt and copper doped zinc oxide powder were successfully fabricated by the sol–gel method at different concentrations (i.e., 5 wt% and 10 wt%). Structural and morphological properties of the samples were studied comparatively. Structural analysis of the samples revealed that all of them were polycrystalline zinc oxide in nature; possessing hexagonal wurtzite structure with (101) preferred orientation. The lattice constants were calculated from the most prominent peak and compared with the standard values. Other structural parameters such as strain, crystallite size, dislocation density, stacking fault, and specific surface area were also calculated to have a better investigation. The sensing performance of the samples toward ethanol vapors was investigated for various concentrations of ethanol in air at different operating temperatures in the range of 175–400 °C. The gas sensing performance of the samples was evaluated in terms of gas concentration and operating temperature. Compared to pure zinc oxide, a drastic reduction in the optimal operating temperature and the recovery time was observed after doping. If four different parameters (operating temperature, dynamic response, sensitivity and response and recovery times) were considered simultaneously, the ZCo10 (10% cobalt doped) can be a good option as a sensor material.

Synthesis and Characterization of ZnO-MMT Nanocomposite for Antibacterial Activity Studies

ZnO oxide Nanoparticle and ZnO oxide with Montmorillonite nanocomposite were prepared by an environmentally friendly, efficient, and inexpensive method that was synthesized using the chemical method. ZnO nanoparticles as an effective antibacterial material were immobilized on the surface of montmorillonite (MMT). The objectives of this paper are to summarize our research activities in (a) developing processes to dispersenanomaterials (undoped and doped zinc oxide powders) in the polymers matrix, (b) using X-ray diffraction (XRD), Fourier Transform Infra-Red Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM) and Thermo Gravimetric Analysis (TGA) techniques to characterize polymer matrix structures, (c) studying structure-property relationship of these types of new materials, and (d) evaluating the antibacterial performance of these materials for different applications. The results showed that the ZnO nanocomposite was uniformly dispersed in the polymer matrix and the particles remained their average size (20 - 150 nm) before incorporation into the polymer matrix.
 Keywords: Zinc Oxide nanoparticle, Montmorillonite, FTIR, Antibacterial activity

Nano-Flower Structure of Indium and Gallium doped Zinc Oxide Powder

Flower-like zinc oxide nanostructures have been successfully fabricated by various methods such as chemical vapor deposition, vapor phase transport deposition, thermal evaporation, hydrothermal, sol-gel and template growth methods. Zinc oxide doped with indium and gallium can demonstrate the potential utilization in electronic application for its semiconductor characteristic and the nanostructure of this doped material can enhance its property. In this study, indium and gallium doped zinc oxide nano-structures were prepared by ease method of hydrothermal process, which can well control the morphologies of zinc oxide nanostructure. The concentration percentage of dopants including indium and gallium were varied up to the limitation of synthesis. The dependence on doping content of indium and gallium on the particle morphologies and specific surface area of the samples was investigated systematically. The atomic arrangement and surface properties of synthesized samples were studied according to the measured results obtained by x-ray diffraction, x-ray photoelectron spectroscopy, field emission scanning electron microscope and Brunauer-Emmett-Teller measurement. According to the results, the obtained sample nanostructures are in the size of hundred nanometers with the shape in sheet-like and/or needle-like flower structures. However, the nano-flower structure is found to be disappeared beyond some specific high percentage of the dopant above 15%. The amount of doped indium and gallium are also found in XPS measurement and the substitution of doped atoms in zinc oxide crystal system are also showed in XRD investigation.

Preparation of excellent electrical conductivity aluminum doped zinc oxide powders by one-step solvothermal method

In this work, aluminum-doped zinc oxide (AZO) powders have been prepared by one-step solvent method. AZO powders with different reaction conditions have been studied for the impact on the structure and electrical properties. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscope (TEM), four-probe techniques were used to characterize the surface morphology and electrical properties of all AZO powders. The result showed that the resistivity of the AZO powders decreased from 187.1 Ωm to 14.6 Ωm when the Al doping concentration was 3%, the reaction temperature was 250 °C, the precipitant NaOH concentration was 0.5 mol·L−1, PEG-1000 was used as dispersant.

Reddish emission of europium doped zinc oxide nanophosphor prepared through precipitation route using sodium borohydride

The main objective of this research work is to develop a desired reddish emission of europium (Eu)-doped zinc oxide (ZnO) nanophosphor, prepared through precipitation route using sodium borohydride (NaBH4), as a precipitating agent and also study its structure, powder morphology as well as photoluminescence characteristics, especially asymmetric ratio or colour purity. X-ray diffraction of the calcined (600 °C) Eu (3 mol%)-doped ZnO powders confirmed the presence of pure phase ZnO and also suggested that the europium ions are incorporated in the lattice sites of Zn ions due to the increase in lattice volume as well as peak (101) shifting towards the lower angle. FESEM and TEM analysis confirmed that the particles of Eu-doped ZnO are elongated or elliptical rod-like, having length in the range of 200 nm – 400 nm as well as polyhedral in shape. Photoluminescence behaviour indicate an intense broad transition of 5D0→7F2 (compared to transition of 5D0→7F1) corresponds to red emission, when the sample was excited at 464 nm. The ratio of integrated maximum emission intensities between 5D0 → 7F2 and 5D0 → 7F1 transitions was found to be ∼5.9. The value of asymmetric ratio or colour purity and the position of CIE coordinates suggested that the Eu-doped ZnO nanopowders may be used as red emitting phosphor material.

Preparation of Rod-like Aluminum Doped Zinc Oxide Powders by Sol-gel Technique Using Metal Chlorides and Acetylacetone Precursors

Al-doped ZnO (AZO) powders were prepared by using metal chloride precursors and the sol-gel technique. IR peaks observed at 1590 cm-1 and 1620 cm-1 indicated the formation of metal chelate as a consequence of the addition of acetylacetone to the metal chloride solution. TG-DSC analysis of the AZO gels confirmed the formation of metal chelate as evidenced by the development of several weight loss peaks accompanied by the introduction of new endothermic peaks. The resulting AZO gels were annealed at 500, 600, and 800 °C to study the effect of annealing temperature. XRD and SEM results showed that crystallization of AZO gels takes place around 600 °C. Hexagonal wurtzite structure was identified as the main phase for all the samples. In addition, small shift of the XRD (002) peak coupled with XPS results from the AZO powders confirmed the successful doping of the ZnO powders. Micron sized rod-like AZO powders were uniform in dimension and morphology and remained stable even at 800 °C.

Ga-doped ZnO nanoparticles synthesized by sonochemical-assisted process

In this work, the experimental work has been conducted on the synthesis of Gallium (Ga)- doped zinc oxide (ZnO) nanoparticles with different doping concentration (0-5% at.) via sonochemical process. The precursors of Ga-doped ZnO nanoparticle were sourced by zinc acetate dehydrate and gallium (III) nitrate hydrate, respectively. Ammonia (NH3) was chosen as a precipitating agent in sonochemical process. The sonochemical time was operated for 10 min by a direct-immersion ultrasonic horn using Sonic model VCX 750 (750W, 20 KHz). Structural properties and morphologies were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that Ga doped ZnO powder after the synthesis were obtained in ultrafine structure that different form with pure ZnO. XRD analysis revealed that the pattern of Ga doped ZnO powder showed good crystallinity with the wurtzite structure due to the preferred orientation direction and crystallization. Ga doping concentration plays a key role in significant change of ZnO structures.

Effects of hydrogen annealing and codoping (Mn, Fe, Ni, Ga, Y) of nanocrystalline Cu-doped ZnO dilute magnetic semiconductor

Zinc oxide (ZnO) codoped with Cu and M ions (M = Mn, Fe, Ni, Ga, Y) powders were synthesised by simultaneous thermal co-decomposition of a mixture of zinc and metal complexes. The synthesised chemical formula for the prepared solid solution is Zn 0.97 Cu 0.01 M 0.02 O. X-ray diffraction (XRD) analysis confirms the formation of single nanocrystalline structure of the as-prepared powders, thus, both Cu and M ions were incorporated into ZnO lattice forming solid solutions. Magnetic measurements reveal that all the as-synthesised doped ZnO powders gained partial (RT-FM) properties but with different strength and BH-behaviour depends on the nature of the doping (M). Furthermore, H 2 post-treatment was subsequently carried out and it was found that the observed RT-FM is enhanced. Very interestingly, in case of Ni dopant, the whole powder becomes completely ferromagnetic with coercivity (H c ), remanence (M r ) and saturation magnetisation (M s ) of 133.6 Oe, 1.086 memu/g and 4.959 memu/g, respectively. The value of Ms was increased by ~ 95% in comparison with as-prepared.

Optical studies of nano-structured La-doped ZnO prepared by combustion method

Coral-shaped nano-structured zinc oxide (ZnO) was successfully synthesized and La-doped via a facile combustion process using glycine as a fuel. The auto-ignition (at ∼185°C) of viscous reactants zinc nitrate and glycine resulted in ZnO powders. Hexagonal wurtzite structure of pure and doped ZnO powder was confirmed by X-ray powder diffraction analysis. The transmission electron micrograph shows that the nano-structured ZnO is coral-shaped and possess maximal pore (∼10–50nm pore size) density in it and the grain size is approximately about 15nm. Addition of dopants subsequently alters the structural and optical properties which were confirmed by UV–VIS studies.

Photodegradation of phenol and benzoic acid by sol–gel-synthesized alkali metal-doped ZnO

The effect of three alkali metal dopants on the photocatalytic properties of zinc oxide (ZnO) was investigated. Crystallized powders of ZnO doped with 10% lithium, sodium and potassium synthesized by a sol–gel process with zinc acetate and oxalic acid precursors were characterized by X-ray diffraction, scanning electron microscopy, UV–Vis diffuse reflectance and nitrogen adsorption isotherms. Photocatalytic activity under ultraviolet irradiation of undoped and doped ZnO powders was tested by degradation of phenol and benzoic acid, chosen as model organic pollutants. Doping ZnO with lithium, sodium and potassium increases the crystallinity of powders and reduces band gap energy. Comparison of photocatalytic activity of undoped and doped ZnO powders demonstrates that doping with sodium and lithium increases the efficiency of degradation of both phenol and benzoic acid.

Synthesis and structure analysis of aluminum doped zinc oxide powders

Hexagonal Al-doped zinc oxide (ZnO) powders with a nominal composition of Zn1−xAlxO (0⩽x⩽0.028) were synthesized by the co-precipitation method. The contents of the Al element in the samples were measured by the inductively coupled plasma-optical emission spectroscopy (ICP-OES) technique. The structures of the Zn1−xAlxO (0⩽x⩽0.028) compounds calcined at 1000 and 1200°C have been determined using the Rietveld full-profile analysis method. Rietveld refinements of the diffraction data indicated that the addition of Al initially has a considerably positive effect on the decreasing of the lattice parameters a and c of Zn1−xAlxO, but the effect becomes very slight and even negative with the further increase of the Al content. The solid solubility limit of Al in ZnO (mole fraction y) is 2.2l%, resulting in Zn0.978Al0.22O. It seems that when the Al content is excessive, Al prefers to form a ZnAl2O4 compound with ZnO, but not to incorporate into the ZnO lattice to occupy the Zn2+ cites. Two phases, [ZnO] (or Al-doped ZnO) and [ZnAl2O4], are obviously segregated in Zn1−xAlxO while the value of x is larger than 0.024. The UV-Vis absorption spectra show that the Al-doped ZnO exhibits a red-shift in the absorption edge without reduced transmission compared with pure ZnO, which also confirms that Al ions enter the ZnO lattice and form a Zn1−xAlxO solid solution.

Synthesis and characterization of ZnO – polymer nanocomposites

The introduction of inorganic nanomaterials into polymer matrix has resulted in polymer nanostructured materials exhibiting multi-functional, high performance polymer characteristics beyond what traditional polymer composites possess. Multi-functional features attributable to polymer nanocomposites consist of improved moisture resistance, antibacterial and fungal properties. Zinc oxide powders was prepared via coprecipitation and used as inorganic materials; polyvinylalcohole was used as polymer matrix. The technical approach involves the introduction of nanoparticles into polymer matrix whereby nanoparticles has antibacterial characteristics and enhanced inclusion into the polymer matrix. The objectives of this paper are to summarize our research activities in: (a) developing processes to disperse nanomaterials (undoped and doped zinc oxide powders) in the polymers matrix, (b) using optical microscopy and scanning electron microscopy (SEM) techniques to characterize polymer matrix structures, (c) studying structure-property relationship of these types of new materials, and (d) evaluating the antibacterial performance of these materials for different applications. The results also show that the ZnO nanoparticles were uniformly dispersed in the polymer matrix and the particles remained their original size (20–150 nm) before incorporation into the polymer matrix.

Fabrication of High Performance Multilayer ZnO Varistors with Chemically Synthesized Doped Zinc Oxide Powder

Two types of multilayer ZnO varistors are prepared by the chemically synthesized (CS) powder and the mixed oxide (MO) powder. The ceramic microstructure analysis shows that the multilayer variestor (MLV) ceramic prepared by the CS powder has the fine grain, the homogeneous distribution of grain size and the uniform dopant distribution. The CS powder prepared multilayer ZnO varistors display better electrical properties, including higher nonlinear coefficient, higher breakdown voltage, higher peak current, lower leakage current and lower clamping voltage, than those made by the mixed oxide powder. All these superior electrical properties are attributed to the CS powder, which makes more uniform dopant distribution throughout the multilayer ZnO varistors. The homogeneous distribution for the various dopants in the varistor ceramic has been achieved by the chemically synthesized doped ZnO powder. Therefore, the chemically synthesized powder can be used in the manufacture of high performance multilayer ZnO varistors.

Elaboration and Characterization of ZnO Transition Metal (Co, Mn, Ni, Fe) Doped Aerogel Nanoparticles

ABSTRACTNanocrystalline transition metal (TM=Co, Mn, Ni, Fe) doped zinc oxide powders have been elaborated by a new protocol based on slow hydrolyse of zinc acetate dissolved in methanol and supercritical drying in ethyl alcohol. The powders have a narrow size distribution with an average value of ∼ 25nm. Electron microscopy characterization showed that the size of the ZnO:TM particles did not change significantly for the different dopants. High doping levels of up to [TM] =0.25 have been investigated. X-ray diffraction studies showed the formation of the ZnO wurtzite phase for all dopants but secondary phases are equally detected. High temperature ferromagnetism was observed for Ni and Co doped powders whereas Mn doped powders showed only antiferromagnetic interactions. EPR spectroscopy indicates that the magnetism is related to the presence of extrinsic phases.

XRD and Photoluminescence Studies of Pure and In<sub>2</sub>O<sub>3</sub> Doped ZnO Nanophases

ZnO oxide is a promising material for optoelectronics because of its wide and direct gap (Eg=3.4 eV). Pure and doped zinc oxide powders of various grain sizes have been synthesized by vaporisation-condensation method using a solar furnace. The initial powders contained from 0 to 5 In2O3 mol % . X-ray diffraction technique (XRD) has been used to measure the lattice parameter and the grain size as a function of the composition, the results show the appearance of the spinel phase Zn5In2O8 in the micopowders and the decrease of the grain size of nanopowders as the In concentration increases for all considered compositions. The photoluminescence spectra revealed the presence of two main transitions at 3.31 and 3.36 eV, a shift of the excitonic peaks towards the lower energies, a drastic reduction of the exciton bound to donor emission from the doped material and a large broadening of the excitonic emission in In doped nanopowder.

Strong red up-conversion in Er3+ doped zinc oxide powder prepared by fluoride salt decomposition method

Er 3+ :ZnO powder has been prepared by fluoride salt decomposition method. Upon continuous wave excitation around 980 nm, Er 3+ :ZnO powder exhibit intense red emission originating from the 4 F 9/2 level of Er 3+ . The ratio of integrated emission at 650 nm to that at 540 nm is 21:1 with excitation of a diode laser of 10 mW at room temperature. The up-conversion mechanism has been discussed. It is believed the energy transfer processes that occur among the Er 3+ ions bring out the strong red emission.

Photoluminescence and photodissociation properties of pure and In2O3 doped ZnO nanophases

Pure and doped zinc oxide powders of various grain sizes have been synthesized by sublimation-condensation technique using a solar furnace. The initial powders contained from 0 to 5% mol of In2O3. X-ray diffraction technique (XRD) has been used to measure the lattice parameters and the grain size. The Indium concentration in the nanopowders was determined by XPS. XRD showed the formation of the spinel phase Zn5In2O8 in the micropowders as the concentration of indium exceeded 2.5% mol. In addition, the grain size of nanopowders decreases as the In concentration increases for all considered compositions. The photoluminescence spectra showed a drastic reduction of the exciton bound to a donor and an important broadening of the corresponding line as a result of the In doping. The photocatalytic properties of ZnO and TiO2 powders were investigated using the Monoluniron as septicide. The results showed that the photodegradation of the molecule was significantly faster when using pure ZnO nanopowder. However, the photocatalytic activity of the ZnO nanopowders was drastically reduced by the In doping. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Smart technique for fabrication of zinc oxide varistor

This paper describes a smart and industrially suitable technique for preparing a high performance ZnO varistor from doped zinc oxide powder. A homogeneous distribution of various dopants in the mixed powder has been achieved by coating ZnO powder with a mixed solution of dopants in the form of acetates, nitrates and citrates. The mixed powder on subsequent drying, calcination, and sintering, produced varistors with better nonlinear electrical properties (α = 51) compared to varistors prepared from conventional oxide mixing technique (α = 30). The better nonlinear properties of solution coating route varistors have been attributed to the presence of uniform potential barriers throughout the entire microstructure, which in turn is credited to the uniform distribution of dopant ions at each grain and grain boundary region.

High Performance Varistor Discs Obtained from Chemically Synthesized Doped Zinc Oxide Powder

The ceramic microstructure, the chemical homogeneity of specific dopants and the mechanical integrity of a varistor disc are critical parameters in determining the transient voltage suppression features of these devices. The material properties and overall quality of the starting ceramic powders used to produce such components are essential in achieving the desired properties. The present work describes a novel chemical method developed to produce doped zinc oxide powders and an industrial scale manufacturing process for the production of final varistor blocks for surge arrester applications. The results are compared with those obtained when using standard varistor powder made by the mixed oxide route is used. All the fundamental electrical properties of the discs have been determined and correlated with the relevant manufacturing steps.