Synthesis and Structural Characterization of Three-Layer Aurivillius Ceramics
Date
2003-09
Authors
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Journal ISSN
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Publisher
New York State College of Ceramics at Alfred University. Kazuo Inamori School of Engineering.
Abstract
The three layer Aurivillius crystal structure was investigated for use as an ionic conductor. Sample synthesis was investigated using high temperature x-ray diffraction (HTXRD)
for a range of compounds, using solid state synthesis and the polymerized complex method.
Isothermal Avrami type kinetics studies were performed on Bi4Ti3O12 using in situ HTXRD
and quantitative analysis performed via Rietveld refinements using TOPAS. The kinetics
analysis yielded Avrami exponents of approximately 0.54, which fell in the range of the
diffusion controlled reaction mechanisms. The activation energy over a range of temper-
atures was calculated to be on the order of 140kJ/mol. Crystal structure refinements
were performed on the Bi2Sr2¡xAxNb2TiO12 (A = Ca,Ba, x = 0.5, 1) series using combined
x-ray and neutron diffraction Rietveld refinements. Refinements indicated a static disorder between the Bi and A sites, and between the Nb and Ti sites. A-site lattice strain
investigated via the bond valence method reveals a linear increase in strain with the size
of the substituted alkaline earth cation. Furthermore, large isotropic thermal parameters
for the O1 and O4 oxygen sites reveal possible oxygen vacancy formation as a result of
unresolved strain between the A and Ti layers of the structure. Oxygen stoichiometry
is found to decrease as the size of the a lattice parameter decreases. Synthesis of non-
stoichiometric three-layer phases was accomplished by aliovalent substitution and via forced
site-mixing. Neither method produced samples with conductivities greater than 10^-3 S/cm at
900±C. Non-stoichiometric compositions follow similar structural trends to those observed
in the stoichiometric crystal structure refinements. Increased numbers of oxygen vacancies
were recorded than anticipated from the dopants. The number of extra vacancies corresponds well with the amount shown in the stoichiometric compositions. Based on the
conductivity and number of charge carriers, the mobilities of the charge carriers are very
low, on the order of 10^-7 to 10^-10 cm2/V sec at 1000˚C.
Description
Advisory committee members: Doreen Edwards, Walter Schulze, Vasantha Amarakoon. Dissertation completed in partial fulfillment of the requirements for the degree of Doctorate of Philosophy in Ceramics at the Kazuo Inamori School of Engineering, New York State College of Ceramics at Alfred University
Type
Thesis