Azis, Rabaah Syahidah (2010) Structure development in sol-gel derived yttrium aluminium oxide, yttrium gallium oxide and their solid solutions. PhD thesis, University of Warwick.

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Abstract

The structural study of the garnet system Y3Al5O12 (YAG) prepared by different sample
preparations (solid-state sintering and sol-gel) is reported. Different sample preparations were
investigated to find a suitable method for obtaining pure YAG. 27Al and 89Y MAS NMR were
used to investigate the short range structure and results are compared to long-range order
information from x-ray diffraction (XRD). These two techniques are comlementary in
detecting phase composition and disorder in samples. There is a challenge in preparing pure
Y3Al5O12 since intermediate phases easily grow when sintered at high temperature, i.e. YAlO3
(YAP), Y4Al2O9 (YAM), Y2O3 (Yttria) and Al2O3 (Corundum). Therefore structural
information on these impurity phases was obtained to compare with samples under study.
Different sample preparations were also used to try to obtain pure YAP and YAM. Since it is
difficult to obtain pure YAG by high temperature solid-state sintering, the sol-gel technique
was used to produce pure YAG at low temperature. In this work, pure YAG has been obtained
at temperatures as low as 800oC using a sol-gel citrate-nitrate with combustion process
(SGCNCT). Other sol-gel syntheses used are: sol-gel glycolate (SGG), citrate-nitrate (SGCN)
and modification of the citrate-nitrate ratio with combustion process (SGCNCT). The
modification of the citrate to nitrate ratio and controlling the mixing temperature as low as 50-
60oC is a novel route to produce pure YAG at low as 800oC. This technique was then used to
prepare different garnet systems, i.e. Y3Ga5O12 (YGG) and also garnet solid solution system,
Y3Al5-xGaxO12. Again, information from NMR was compared with results from XRD to
determine different phase distribution and disorder. The 27Al chemical shift range for different
structural units (e.g. AlO4, AlO5 and AlO6) in YAG allowed the aluminium distribution in
these materials to be refined. This is important when dealing with low temperature amorphous
phases. For example, the AlO5 site cannot be traced using XRD. The work was extended to
study different nuclei, i.e. 89Y and 71Ga NMR. 27Al and 71Ga is a quadrupolar nuclei with
spin, I=5/2 and 3/2, respectively. Extensive broadening of the NMR signal was observed at
some sites due to the quadrupolar interaction and the effect of this on the quantitation of 27Al
and 71Ga NMR is discussed. The substitution of Al and Ga in the garnet system was
investigated. The different distribution of next nearest neighbour atom (nnn) produces a peak
shift in 27Al, 71Ga NMR and also XRD.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QC Physics
Library of Congress Subject Headings (LCSH):	Aluminum-yttrium alloys, Yttrium alloys, Gallium compounds, Garnet -- Synthesis, Sintering
Official Date:	April 2010
Dates:	Date Event April 2010 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Holland, Diane
Sponsors:	Malaysia. Kementerian Pengajian Tinggi [Ministry of Higher Education] ; Universiti Putra Malaysia ; University of Warwick ; Institute of Physics (Great Britain) ; Danmarks Grundforskningsfond [Danish National Research Foundation]
Extent:	xx, 178 leaves : ill., charts
Language:	eng
URI:	http://wrap.warwick.ac.uk/id/eprint/4483

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