Synthesis of gamma and theta alumina phases complemented with first principles calculation

The synthesis of aluminium oxide (alumina) Al2O3 nanopowders has attracted much attention because of its high specific surface area and a large number of defects in its crystalline structure, which make it widely applicable in ceramic applications. In this study, co-precipitation technique was used...

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Main Author:	Jbara, Ahmed Subhi
Format:	Thesis
Language:	English
Published:	2017
Subjects:	QC Physics
Online Access:	http://eprints.utm.my/id/eprint/81785/1/AhmedSubhiJbaraPFS2017.pdf
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spelling	my-utm-ep.817852019-09-29T10:53:51Z Synthesis of gamma and theta alumina phases complemented with first principles calculation 2017-03 Jbara, Ahmed Subhi QC Physics The synthesis of aluminium oxide (alumina) Al2O3 nanopowders has attracted much attention because of its high specific surface area and a large number of defects in its crystalline structure, which make it widely applicable in ceramic applications. In this study, co-precipitation technique was used to synthesize single-phase alumina nanopowders under various annealing temperatures. The crystalline phase, purity, morphology, chemical bonds and optical properties of the prepared powders were characterized by different spectroscopy techniques. To realize a real understanding of phenomena regarding nanoparticles growth, the material on an atomic scale must be studied. In this case, electronic and optical properties of the alumina at atomic scale have also been studied by the first principles within the framework of density functional theory (DFT). The computational approach is based on a full-potential linearized augmented plane wave method (FP-LAPW) within the generalized gradient approximation (GGA), local density approximation (LDA), and modified Becke–Johnson (mBJ) potential. The experimental results show the direct phase transitional behavior of ?-Al2O3 into ?-Al2O3 at annealing temperature of 900ºC. X-ray diffraction (XRD) and Brunauer–Emmett–Teller analysis confirm the existence of alumina nanopowders with particle diameters of < 5 nm, which also can be classified as ultrafine powder. The surface areas of prepared nanopowders were 366.67 m2/g (200ºC) and 100 m2/g (900ºC) for ?-Al2O3 and ?-Al2O3, respectively. The optical results indicate that ?-Al2O3 possesses a lower band gap (5.5 eV), compared to the ?-Al2O3 (5.8 eV). Theoretical results show that these compounds have a direct band gap (G-G) of 5.375 eV and 4.716 eV for ?-Al2O3 and ?-Al2O3, respectively. Several optical parameters of these materials were also investigated. The values of the real part of dielectric constant ( ) are found to be 3.259 and 3.694 for ?-Al2O3 and ?-Al2O3, respectively, while the refractive indices ( ) are found to be 1.806 for ?-Al2O3 and 1.922 for ?-Al2O3. These GGA findings are consistent with the experimental results and are better than the other approximations. There are no salient differences between GGA and LDA results. The present results advocate the use of this material as transparent conducting layer in solar cell structure, which can be operated in a wide energy range. 2017-03 Thesis http://eprints.utm.my/id/eprint/81785/ http://eprints.utm.my/id/eprint/81785/1/AhmedSubhiJbaraPFS2017.pdf application/pdf en public http://dms.library.utm.my:8080/vital/access/manager/Repository/vital:126132 phd doctoral Universiti Teknologi Malaysia, Faculty of Science Faculty of Science
institution	Universiti Teknologi Malaysia
collection	UTM Institutional Repository
language	English
topic	QC Physics
spellingShingle	QC Physics Jbara, Ahmed Subhi Synthesis of gamma and theta alumina phases complemented with first principles calculation
description	The synthesis of aluminium oxide (alumina) Al2O3 nanopowders has attracted much attention because of its high specific surface area and a large number of defects in its crystalline structure, which make it widely applicable in ceramic applications. In this study, co-precipitation technique was used to synthesize single-phase alumina nanopowders under various annealing temperatures. The crystalline phase, purity, morphology, chemical bonds and optical properties of the prepared powders were characterized by different spectroscopy techniques. To realize a real understanding of phenomena regarding nanoparticles growth, the material on an atomic scale must be studied. In this case, electronic and optical properties of the alumina at atomic scale have also been studied by the first principles within the framework of density functional theory (DFT). The computational approach is based on a full-potential linearized augmented plane wave method (FP-LAPW) within the generalized gradient approximation (GGA), local density approximation (LDA), and modified Becke–Johnson (mBJ) potential. The experimental results show the direct phase transitional behavior of ?-Al2O3 into ?-Al2O3 at annealing temperature of 900ºC. X-ray diffraction (XRD) and Brunauer–Emmett–Teller analysis confirm the existence of alumina nanopowders with particle diameters of < 5 nm, which also can be classified as ultrafine powder. The surface areas of prepared nanopowders were 366.67 m2/g (200ºC) and 100 m2/g (900ºC) for ?-Al2O3 and ?-Al2O3, respectively. The optical results indicate that ?-Al2O3 possesses a lower band gap (5.5 eV), compared to the ?-Al2O3 (5.8 eV). Theoretical results show that these compounds have a direct band gap (G-G) of 5.375 eV and 4.716 eV for ?-Al2O3 and ?-Al2O3, respectively. Several optical parameters of these materials were also investigated. The values of the real part of dielectric constant ( ) are found to be 3.259 and 3.694 for ?-Al2O3 and ?-Al2O3, respectively, while the refractive indices ( ) are found to be 1.806 for ?-Al2O3 and 1.922 for ?-Al2O3. These GGA findings are consistent with the experimental results and are better than the other approximations. There are no salient differences between GGA and LDA results. The present results advocate the use of this material as transparent conducting layer in solar cell structure, which can be operated in a wide energy range.
format	Thesis
qualification_name	Doctor of Philosophy (PhD.)
qualification_level	Doctorate
author	Jbara, Ahmed Subhi
author_facet	Jbara, Ahmed Subhi
author_sort	Jbara, Ahmed Subhi
title	Synthesis of gamma and theta alumina phases complemented with first principles calculation
title_short	Synthesis of gamma and theta alumina phases complemented with first principles calculation
title_full	Synthesis of gamma and theta alumina phases complemented with first principles calculation
title_fullStr	Synthesis of gamma and theta alumina phases complemented with first principles calculation
title_full_unstemmed	Synthesis of gamma and theta alumina phases complemented with first principles calculation
title_sort	synthesis of gamma and theta alumina phases complemented with first principles calculation
granting_institution	Universiti Teknologi Malaysia, Faculty of Science
granting_department	Faculty of Science
publishDate	2017
url	http://eprints.utm.my/id/eprint/81785/1/AhmedSubhiJbaraPFS2017.pdf
_version_	1747818413531594752

Synthesis of gamma and theta alumina phases complemented with first principles calculation

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