Aurivillius Phase Oxides for Photocatalytic Applications
New York State College of Ceramics at Alfred University. Kazuo Inamori School of Engineering.
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.
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