Perkins, James M. (2006) Microstructure and properties of (rare earth) doped oxide ceramics. PhD thesis, University of Warwick.

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Abstract

A study of alumina (AI203 ) and magnesium aluminate spinel (MgAb04) was undertaken
with the aim of investigating the changes in properties and microstructural characteristics
upon doping with specific rare earth elements.
Microscopic imaging and analysis of RE doped polycrystalline oxide ceramics has shown
convincing evidence for monolayer segregation of RE cations to grain boundaries. State
of the art aberration corrected scanning transmission electron microscopy (SuperSTEM I
Daresbury Laboratories) has shown monolayer segregation to grain boundaries, and
atomic resolution parallel electron energy loss spectroscopy has confirmed the presence
of the RE cation at the grain boundary position. The region affected by segregation
has been shown to extend no further than one monolayer from the centre of the grain
boundary with RE cations occupying matrix cation boundary sites.
The effect of RE dopants on the powder processing and sintering of high purity commercial
grade precursor powders was investigated. Differences were found between doped
alumina and spinel in the sintering whereby the alumina grain growth was restricted
by grain boundary mobility such that the grain size was reduced for a given sintering
temperature. The grain size of spinel was unaffected by sintering temperature.
Differences in the fracture behaviour between doped alumina and spinel was found.
The alumina samples manifested a change from trans-granular fracture to inter-granular
fracture due to the addition of RE dopants. Spinel did not show such an effect. Alumina
was shown to posess an approximate Hall-Petch relationship between hardness and
grain size for both doped and undoped samples, such that sub-micron grain size samples
posessed high hardness.
Optical characterisation has shown the potential for the use of fine grained RE doped
alumina and spinel samples for hard window applications. A reduction in the grain size
of alumina to below 1 μm leads to a change in the scattering mechanism, thus reducing
low angle scatter and birefringence due to the refractive index mismatch. The benefits
to optical properties are in addition to the benefits in mechanical properties of a submicron
grain structure.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QD Chemistry
Library of Congress Subject Headings (LCSH):	Aluminum oxide, Spinel group, Rare earth metals, Oxide ceramics
Official Date:	April 2006
Dates:	Date Event April 2006 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Lewis, M. H. (Mike H.)
Extent:	[xxiv], 214 leaves
Language:	eng

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