MacDiarmid - Grain Growth Kinetics of ZnOAl Nanocrystalline Powders

The relative proportions of dopant ions incorporated

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Unformatted text preview: ystallographic texture as a result of strongly directional heating). The relative proportions of dopant ions incorporated into zincite lattice sites has previously been related to processing temperatures and heating rates;11 however, this work was limited to a final ex situ ‘snapshot’ of the final products. Understanding the kinetics of ZnO crystallite formation in solÀgels with and without Al present will assist in determining the optimal processing conditions for calcination of ZnO:Al films. ’ EXPERIMENTAL SECTION ZnO:Al gels were synthesized from reaction of aqueous zinc acetate (Scharlau) with 1 mol equiv of citric acid (Scharlau). The liberated acetic acid was removed by rotary evaporation of samples to dryness at 80 °C, redissolving or resuspending the residue in distilled water, and repeating. A 2 mol equiv amount of ethanolamine (Acros) was added to the citrate to solubilize the Zn citrate salt in water. An aluminum citrate solution was prepared from aluminum s-butoxide (Sigma) and anhydrous citric acid (Applichem) (1:1 ratio) in isopropanol. Removal of the solvents under reduced pressure was carried out by rotary evaporation, and the solid residue was redissolved in distilled water to prepare a standard solution. Aliquots were added to the Zn solutions to form mixtures containing Al in concentrations of 0, 1, 2, and 4 mol % with respect to Zn. The Zn concentration of the solutions was standardized at 0.5 mol LÀ1. Received: July 26, 2011 Revised: September 13, 2011 Published: September 19, 2011 21034 dx.doi.org/10.1021/jp207140g | J. Phys. Chem. C 2011, 115, 21034–21040 The Journal of Physical Chemistry C ARTICLE Figure 1. Selected 2θ region of a time series of XRD data for a sample containing 0% Al, heated at 600 °C for 2 h, showing the ZnO 100, 002, and 101 diffraction peaks. To prepare for synchrotron XRD measurements, a thin layer of each solution was applied to the outside of a 0.3 mm diameter quartz capillary and then dried in an oven in air at 75 °C overnight. Calcination experiments were attempted for samples where 0.5 mm diameter quartz capillaries were filled with solution and then dried; however, these were unsuccessful due to the enclosed geometry, which prevents the organic components from diffusing away as the sample was heated. Synchrotron X-ray diffraction experiments were conducted at the Australian Synchrotron on the Powder Diffraction beamline. The X-ray wavelength was 0.77442 Å (∼16 keV). Samples were heated throughout the measurement using a Cyberstar hot air blower. Over the range of temperatures studied, this has an accuracy of (<5 °C. Diffracted X-rays were detected using a Mythen detector spanning 80° (2θ) of arc. Thirty second exposures were used. For each experiment, the capillary sample was first mounted and aligned and a single scan recorded at room temperature. The hot air blower was then moved out from the sample to be heated up. Once the hot air blower was at the desired temperature, it was moved into...
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