Al-doped ZnO Powders Research Articles

Significant Enhancement in the Thermoelectric Performance of Aluminum-Doped ZnO Tuned by Pore Structure.

In this paper, 2 atom % Al-doped ZnO (AZO) was prepared by the co-precipitation method together with sparking plasma sintering (SPS) treatment. The as-synthesized AZO powders show the morphology of hollow hexagonal towers, which result in a high porosity of 50.6% in the bulk sample consolidated by SPS sintering at 400 °C, and the porosity decreases gradually with increasing sintering temperature up to 1000 °C. Positron annihilation measurements reveal that even after sintering at 1000 °C, there are still a considerable number of small pores. A high electrical conductivity of 3 × 105 S m-1 is achieved at room temperature for the AZO sample sintered at 1000 °C, while the absolute values of Seebeck coefficient keep at relatively high values between 59 and 144 μV K-1 in the measurement temperature range of 27-500 °C, leading to a high power factor of 3.4 × 10-3 W m-1 K-2. On the other hand, the pores in AZO act as strong phonon scattering centers, and an extremely low thermal conductivity of 1.5 W m-1 K-1 measured at room temperature is obtained for AZO sintered at 400 °C. Due to the residual pores in the 1000 °C-sintered sample, the thermal conductivity is still relatively low. As a result, a maximum ZT of 0.275 measured at 500 °C is obtained in this sample, which is the highest ZT reported for ZnO around this temperature.

Study of Low Temperature Preparation of Al Doped ZnO Powder and its Photocatalytic Properties

Aluminum doped ZnO crystal powders have been successfully prepared by sol-gel method with low temperature (150°C) crystallization process. The AlNO3 as material dopant were varied by 0.5 wt% and 1.0 wt% relate to 5 mmol of zinc acetate dihydrate as precursor. Degradation of the methylene blue (MB) was used to evaluate the photocatalytic property. The results showed that all ZnO samples have spherical morphology with hexagonal wurtzite crystal structures. The ZnO powder with 0.5 wt % of aluminum has a better photocatalytic property that related to the optical characteristics. The optimum of Al content (0.5wt%) reduces the crystallite size and give some advantages in optical characteristics that directly relate to the increments in photocatalytic behavior. The photodegradation rate of Al doped ZnO 0.5 wt% is increase almost 100% compared with ZnO undoped. The stability and reusability of 0.5 wt% Al doped ZnO as photocatalyst, is also observed by monitoring the photocatalytic behavior under 14 hours irradiation (in three recycle used)

Structural Characterization of ZnO and Al Doped ZnO Powders Synthesis in Aqueous Solutions

Undoped and Al-doped ZnO (AZO) powders have been synthesized by hydrolytic and hydrothermal synthesis from Zn(NO3)2 , AlCl3 using KOH 1M concentraction like hydrolisis agent. The structural properties of prepared powders were studied using XRD and FTIR spectroscopy. Presence of aluminium in the hydrothermal powders is correlated with the presence of Zn-Al hydrotalcite like structure.

Controlling of surface morphology of ZnO nanopowders via precursor material and Al doping

In this paper, the optimization studies on the structural, morphological and electrical properties of undoped and Al doped ZnO nanopowders by microwave assisted hydrothermal method were performed. The ZnO nanopowders were prepared in different zinc acetate and NaOH molarities and after the determination of the best powder conditions, Al doped ZnO powders were obtained under these conditions. The surface morphology of ZnO nanoparticles is influenced by the starting solution type and molarity. Different morphologies of ZnO microstructures were obtained by adjusting the concentration of Zn2+ and OH−. The structural, morphological, electrical and optical properties of these nanopowders were investigated using X-ray diffractometer, scanning electron microscopy, DC electrical measurements and reflectance measurements. The incorporation of Al in ZnO nanopowder was also changed the morphology of these powders. The presence of Al+3 ions in ZnO nanopowder was determined by XPS measurements. Conductivity and resistivity values of ZnO nanopowders varied with Al incorporation. As the amount of Al in ZnO increases, their resistivities have decreased and their conductivities have increased. The optical band values of Al doped ZnO nanopowders were found via reflectance measurements using kubelka-munk function. As a result of Burstein-moss effect, the optical band values increased with the increase of the Al dopant.

Structural, optical and charge density analysis of Al doped ZnO Materials

The hexagonal structured Zn1−xAlxO (x = 0.00, 0.04, 0.06, 0.08 and 0.10) materials was synthesized by co-precipitation method. Structural, morphological and photoluminescence properties of Al doped ZnO powders were investigated by powder X-ray diffraction, scanning electron microscopy and photoluminescence characterizations, respectively. Structural analysis was done by Rietveld refinement technique. The spherical shaped morphology was observed in ZnO:Al powders. The bonding features were analyzed by using electron density distribution studies and the photoluminescence properties of Zn1−xAlxO (x = 0.00, 0.04, 0.06, 0.08 and 0.10) was also revealed.

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.

Thermal conductivity and stability of Al-doped ZnO nanostructured ceramics

Pure and Al-doped ZnO powders have been sintered by Spark Plasma Sintering. Al doping allows the ceramics to reach a relative density greater than 90% at a sintering temperature of 500 °C. The morphology of powder nanoparticles impacts the final grain size of the sintered bulk compounds. A ceramic sintered from isotropic nanoparticles of 30 nm in diameter can reach an average grain size of 110 nm, whereas a ceramic sintered from platelets and isotropic nanoparticles exhibits an average grain size in the submicrometric range. The influence of ceramic grain size on the thermal conductivity has been investigated. It shows that substantial decrease of the grain size from several microns down to 100 nm reduces the thermal conductivity from 29.5 to 7.8 W/m K at 100 °C. The stability of nanostructured ceramic has also been checked. After SPS, an annealing at 500 °C in air also leads to grain growth.

Structural, morphological and optical characterizations of ZnO:Al thin films grown on silicon substrates by pulsed laser deposition

The pulsed laser deposition (PLD) technique is used to grow Al-doped ZnO (AZO) thin films at 500 ° C on silicon substrates under vacuum or oxygen gas background from ablating AZO nanoparticle targets synthesized via the sol-gel process. The structural, morphological and optical properties were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and spectroscopic ellipsometry (SE) techniques. XRD and TEM images show that AZO powder has a wurtzite-type structure and is composed of small prismatic-like shape nanoparticles with an average size of 30nm. The structural properties of the AZO films grown under oxygen show no significant changes compared to those of the film grown under vacuum. However, the optical properties show a dependence on the growth conditions of the AZO films. Highly c -axis-oriented AZO thin films were obtained with grain size ∼ 15 nm. The stress in the AZO films is tensile as measured from the c -parameter. The dielectric function, the refractive index and the extinction coefficient as a function of the photon energy for the AZO films were determined by using spectroscopic ellipsometry measurements in the photon energy region from 1 to 6eV. The band gap energy was observed to slightly decrease in the presence of the O2 gas background and this may be attributed to the stress. The surface and volume energy loss functions are calculated and exhibit different behaviors in the energy range 1-6eV. Refractive indices of 1.9-2.1 in the visible region were obtained for the AZO films. Also, the electronic carrier concentration appears to be related to the presence of O2 during the growth process.

Methylene blue photocatalytic degradation under visible irradiation of Al doped ZnO powders by hydrothermal synthesis sensitized with octa-iso-pentyloxyphthalocyanine lead

AZO powders were sensitized through chemisorption method by octa-iso-pentyloxy phthalocyanine lead and characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results showed that after sensitization process AZO photo physical properties improved greatly in visible regions. Photocatalytic degradation of methylene blue was studied under visible irradiation in aqueous solution and the pseudo first order model was used to obtain kinetic information of the photocatalytic degradation. The results indicated that photocatalytic activities of PbPc(iso-PeO)8-AZO were better than of AZO powders.

Effect of urea on the synthesis of Al-doped ZnO nanoparticle and its adsorptive properties for organic pollutants

Al-doped ZnO nanoparticles were synthesized through a solution combustion synthesis derived from zinc nitrate, aluminum nitrate and urea mixed solution. The effects of fuel/oxidizer molar ratio (ϕ) on the morphology, physical properties, and adsorptive properties for organic pollutants of Al-doped ZnO have been systematically investigated. The results indicated that the homogeneous Al-doped ZnO powders might be prepared by selecting an optimum ϕ in solution. The results of XRD pointed toward a significant pure wurtzite ZnO phase for 2mol% Al-doped ZnO powders prepared with different ϕ. With the increase of ϕ, the morphology of the products changes from clusters of irregular particles into flakes. A well-distributed and smaller crystallite size varying from 30nm to 50nm was observed from 2mol% Al-doped ZnO sample (ϕ=4). In addition, the Al-doped ZnO sample (ϕ=4) showed a higher absorption ability and shorter equilibration time for organic pollutants compared to other samples.

Influence of Transition Metal (Cu, Al) Ions Doping on Structural and Optical Properties of ZnO Nanopowders

Al doped ZnO, Cu doped ZnO Nanoparticles were successfully synthesized by Sol-Gel Method and Zinc Chloride(ZnCl2),Potassium Hydroxide(KOH), Aluminum Nitrate(Al(NO3)2, Copper Nitrate (Cu(NO3)2) and Ethanol(C2H6O) were used as a precursors . The structural and optical properties of Nanoparticles were analyzed by means of XRD (X-Ray Diffraction), SEM (Scanning Electron Microscopy) and FTIR (Fourier Transform Infra Red spectroscopy). The results of Cu doped ZnO and Al-doped ZnO nanoparticles were also compared to investigate the structural and optical properties. XRD analysis reveals that both the samples crystallizes in hexagonal wurtzite structure and exhibit no impurity phase . The crystalline size of 28.43nm and 6.87nm are obtained in Cu doped ZnO and Al doped ZnO Nanoparticles. Therefore, the decrease in the crystalline size can be seen with the change in doping element. The optical properties also depend on the type of doping due to the Al-N bond intensity, The Al doped ZnO powder is stronger than Cu doped ZnO.

Al-doped ZnO nanostructured powders by emulsion detonation synthesis – Improving materials for high quality sputtering targets manufacturing

Abstract Emulsion detonation synthesis method was used to produce undoped and Al-doped ZnO nanostructured powders (0.5–2.0 wt.% Al2O3). The synthesized powders present a controlled composition and a morphology which is independent on the doping level. The XRD results indicate wurtzite as the single phase for undoped ZnO and the presence of gahnite as secondary phase for Al-doped ZnO powders. The sintering behavior of each powder was studied based on their linear shrinkage and shrinkage rate curves, showing the high sinterability of the powders. Activation energies for densification in the earlier stage were calculated for all compositions and possible sintering mechanisms are suggested depending on the doping level. The high chemical homogeneity and sinterability and the lower electrical resistivity of the bulk Al-doped sintered samples demonstrates the feasibility of emulsion detonation synthesis for the production of high quality Al-doped ZnO powders to be used in ceramic sputtering targets manufacture.

Optical and Electrical Properties of Hierarchical Nanostructured Al‐Doped ZnO Powders Prepared through a Mild Solution Route

Hierarchical nanostructured Al-doped ZnO (AZO) powders were successfully prepared through a mild solution route. The crystal structure and morphology of AZO were determined by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The morphology of the samples changed from random flower-like nanostructures to uniform flower-like hierarchical nanostructures with different Al doping contents. The optical and electrical properties of AZO were studied by UV/Vis spectroscopy and four-point probe. The optical band gap of AZO increased initially but then decreased as the Al content was increased owing to the Burstein–Mass effect and the many-body effect. Conversely, the electrical resistivity of the AZO powders first decreased and then increased with the Al doping content increasing because of changes in the electron and dopant concentrations. AZO exhibited the smallest electrical resistivity with an Al doping content of 1.0 at-%, which is two orders of magnitude smaller than the electrical resistivity of ZnO.

Microwave dielectric properties of Al-doped ZnO powders synthesized by coprecipitation method

Al-doped ZnO (AZO) powders with different Al concentrations were synthesized by coprecipitation method. Crystal structural and dielectric properties of the powders as a function of aluminum doping concentration as well as annealing temperature were investigated. The XRD results reveal that Al atoms are doped into ZnO lattice successfully and all the samples are polycrystalline with a hexagonal wurtzite structure. The real part (ε′) and imaginary part (ε″) of the complex permittivity of the powders were carried out by a vector network analyzer in the microwave frequency range of 8.2–12.4 GHz. The results show that the ε′ and ε″ of the doped ZnO powders increase with the doping content and both of them are higher than that of the pure one. For the AZO powder with 7 mol% Al, both ε′ and ε″ increase firstly and then decrease with increasing annealing temperature.

Study of the Photocatalytic Activity of Na and Al-doped ZnO Powders

Na and Al-doped ZnO nano-powders were prepared by the sol-gel method. The XRD results indicated that all samples revealed a wurtzite-type hexagonal crystalline structure and the grain size of Al-doped ZnO decreases with increasing Al doping. The grain size of Na-doped ZnO is about 50 nm. Photocatalytic degradation of the methyl orange solution under the light of wavelength of 254 nm was performed to investigate the photocatalytic activity of Na, Al-doped ZnO powders. The results showed that Al dopant can greatly improve the photocatalytic activity of ZnO powder. The enhancement of photocatalytic activity of doped ZnO powers is mainly due to their smaller particle size and capability for reducing the electron hole pair recombination.

Aluminum doped zinc oxide sputtering targets obtained from nanostructured powders: Processing and application

Abstract This work reports the production of ceramic targets based on nanostructured Al-doped ZnO (AZO) powders for sputtering applications. The nanostructured powder is obtained by a new patented process based on the detonation of an emulsion containing both Zn and Al metal precursors in the final proportion of 98:2 wt% (ZnO:Al2O3), through which the Al contains is highly uniform distributed over ZnO. Due to the nanostructured powder characteristics, the targets can be sintered at substantially lower temperatures (1150–1250 °C) by conventional sintering, contributing to production costs reduction of ceramic targets and consequently the costs of photovoltaic and displays industries. Electrical resistivity values around 3.0–7.0 × 10−3 Ω cm have been obtained depending on final microstructure of the targets. The electro-optical properties of the films produced at room temperature with thicknesses around 360 nm, besides being highly uniform exhibit a resistivity of about 1 × 10−3 Ω cm and a transmittance in the visible range above 90%.

Influence of annealing atmosphere on optical properties of Al‐doped ZnO powders

AbstractWe systematically studied the influences of annealing atmosphere on the structural and optical properties of Al‐doped ZnO (AZO) powders by performing anneals in N2, Ar2, H2 and O2 atmospheres. The results indicated that the optical properties were highly influenced by the annealing atmosphere, which were more pronounced for the AZO powders annealed in forming gas and an oxygen atmosphere. The E1 (LO) vibration mode in the Raman spectra exhibits a good correlation with the green emission and is demonstrated to be originated from VO defects. We conclude that both VO and Oi defects give rise to the green photoluminescence in ZnO, and each will play a dominant role in oxygen‐deficient and oxygen‐rich environments, respectively.magnified image

Structural and luminescence properties of pure and Al-doped ZnO nanopowders

Abstract Pure and Al doped zinc oxide nanopowders have been synthesized by sol–gel route. This is a simple and inexpensive method permitting to obtain a very small grain size powders. Zinc acetate dehydrate was first dissolved in a mixture of 2-methoxyethanol and mono-ethanolamine (MEA) solution, were used as a solvent and stabilizer respectively and doped with a quantity of aluminum nitrate, varying from 0 to 10 mol%. The obtained gel is then calcinated in air at 500 °C. The samples are characterized by XRD, SEM and photoluminescence (PL) studies. The XRD results indicate that pure and Al-doped ZnO powders are solid solutions crystallizing in pure wurtzite structure, and consisted of a mixture of nanoparticles with grain size between 23 and 36 nm. The grain size decreases strongly with increasing Al concentration and reaches its lowest value at 5 mol% Al. The PL spectra show that the most important establishment is that the powders show luminescence peaks from green to ultraviolet light, and thus can be used to manufacture transmitters using these emissions. The peaks connected to the blue luminescence are the most intense, and they are generated by transitions involving (Zn i ). The SEM images show a formation of pebbles with sizes decreasing with Al concentration and a morphology evaluating, qualitatively, from pebbles without cavities to highly porous ones.

Preparation of AZO/acrylic Resin Transparent Insulation Coating

Transparent Al doped ZnO (AZO)/acrylic resin composites, as glass thermal insulation coating, were prepared by incorporating AZO nanoparticles into transparent acrylic resin matrix. Firstly, AZO powders were synthesized by sol-gel method. Then transparent heat-insulation coating of AZO/acrylic resin was prepared by the blending method. The results show that the transparent heat-insulation coating had good chemical stability and mechanical properties; under the irradiation of infrared lamp for 10 minutes, the temperature difference between the coated glass and bland glass achieved 13.8oC.

Infrared absorptive properties of Al-doped ZnO divided powder

Al-doped ZnO powders were synthesised by a Pechini process in order to obtain visible non-absorbent and near-Infrared absorbent particles. Firstly, it has been shown that synthesis under argon combined with the lowest synthesis temperatures (700 °C) allows getting the optimal properties for pure ZnO compounds due to creation of n-type defects segregated on oxide grain surface (Zn/O ratio superior to 1). Nevertheless, the near-Infrared absorption properties of the pure ZnO compounds remain low. The Al 3+ doping of ZnO compounds was then investigated. The Al solubility limit inside ZnO doped compounds decreases drastically with the grain size, i.e. with the synthesis temperature. Then, the Al cations distribution varies inside ZnO grains, Al 3+ segregation at the grain surfaces taking place for high synthesis temperatures. The optimal optical properties (high near-Infrared absorption) are reached combining Al-doping and adequate synthesis conditions: annealing under argon at low temperatures. In these conditions, the highest extrinsic (via Al doping) and intrinsic n-types defects rates are indeed reached.