Keeble, Dean Samuel (2009) An investigation of the relationship between the structure and properties of some stacked perovskites. PhD thesis, University of Warwick.

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Abstract

This thesis discusses a comprehensive study of the structure and properties of selected
stacked perovskites using non-ambient powder and single-crystal x-ray diffraction, powder
neutron diffraction, birefringence microscopy and dielectric spectroscopy. The major
portion of this work focuses on materials forming in Aurivillius phases, with the general
chemical formula [Bi2O2]2+[An−1BnO3n+1]2−, and containing n perovskite layers sandwiched
between
fluorite-like interstices. Comparisons are made between the structure
and properties of the isomorphous materials SrBi2Nb2O9 and BaBi2Nb2O9, and the
ferroelectric phase transition in SrBi2Nb2O9 is compared to that in SrBi2Ta2O9. The
latter shows two distinct phase transitions upon cooling from the high temperature
phase: a ferroelastic transition to space group Amam at 848 K, followed by a ferroelectric
transition to A21am at 608 K. By contrast, the transition in SrBi2Nb2O9 does
not go via the intermediate Amam phase, as is demonstrated using both structural and
property measurements. It is also shown that in a material that is both ferroelectric and
ferroelastic, the individual contributions to the birefringence of strain and polarization
can be isolated using birefringence microsocopy by applying the principles of Landau
theory to extract the two contributions. The structure and properties of a number
of other materials within the general class of ferroelectrics are investigated using similar
techniques, in particular, single-crystal x-ray diffraction is used to reinvestigate the
room-temperature structure of BaTiO3 following prominent reports of monoclinicity of
this phase. Quantitative investigation of the (101) ferroelastic twinning in these crystals
was also undertaken. In addition, evidence for the existence of a ferroelectric phase
transition in CsBiNb2O7 is derived from the results of powder neutron diffraction as a
function of temperature. The effect of substituting
fluorine on to the anion site on both
the structure and properties of ferroelectric stacked perovskites is also investigated, and
is shown to have a radical effect on the the ferroelectric properties of the material, as
well as on their phase formation.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QC Physics Q Science > QE Geology
Library of Congress Subject Headings (LCSH):	Perovskite, Ferroelectric crystals
Official Date:	September 2009
Dates:	Date Event September 2009 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Thomas, Pam A.
Sponsors:	Engineering and Physical Sciences Research Council (EPSRC) EP/C008243/1 ; Advantage West Midlands
Extent:	xvii, 146 leaves : ill., charts
Language:	eng

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