Aurivillius Phase Oxides for Photocatalytic Applications
Date
2010-09
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 systematic design of materials for energy production and remediation of
environmental concerns, based on direct knowledge of the structural and optical
absorption characteristics of layered and traditional perovskites, is desirable for use in
rational photocatalyst development. Aurivillius phase ceramic oxides have been
suggested as potential candidates for photocatalytic water splitting applications based
on the structural similarities between this class of materials and titanium dioxide, namely,
transition metals in octahedral coordination with oxygen.
Structural characterization of the three-layer lanthanide titanate Aurivillius oxides
Bi2A2Ti3O12 (A2 = La2, Pr2, Nd2, LaPr, LaNd, PrNd) via combined Rietveld refinements of
x-ray and neutron powder diffraction data has revealed that these materials reside in the
orthorhombic space group B2cb. We have demonstrated that the optical band gaps for
the three-layer lanthanide titanates can be red shifted by as much as 0.3 eV via
combined structural and electronegative (bismuth replacement) means and exhibit a
Vegard type relationship between band gap and chemical composition over the range of
compositions tested (A2 = La2, Pr2, Nd2, LaPr, LaNd, PrNd, LaBi, PrBi, NdBi, La0.5Nd0.5Bi,
Pr0.5Nd0.5Bi, Bi2). Additionally, the band gaps for these materials can be correlated with
a single TiO6 octahedron and the manipulation of its Ti-O bond lengths.
A method of quantification of BX6 octahedral anion distortions in traditional ferroic
perovskites and layered perovskites has been developed based on Rietveld refinement
of neutron diffraction data and vectorial analysis. Quantification of the octahedral
distortion characteristics of the archetype perovskites via a survey of data contained
within the Inorganic Crystal Structure Database (ICSD) has been completed. A
preliminary link between antiferroelectric double hysteresis behavior and octahedral
distortions in traditional perovskites has been established for the compounds PbZrO3,
Pb2WMgO6, PbHfO3 and NaNbO3. Similar to traditional perovskites, octahedral
distortions in the layered perovskites have been demonstrated, quantified and shown to
trend with an average A-site cations’ ionic radius below 1.4 Å. Anatase, the
photocatalytic polymorph of titanium dioxide, exhibits a similar distorted TiO6 octahedral
environment and its structure was analyzed and compared with that of the Aurivillius
oxides.
Description
Advisory committee members: Steven Pilgrim, Doreen Edwards, Alastair Cormack. 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