Title:
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Aspects of strontium titanate nanomaterials
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Strontium titanate (SrTi03) is a perovskite material with diverse physical properties.
Many of its properties are associated with its atomic structure, such as quantum
paraelectricity, structural phase transitions, and extrinsically induced ferroelectricity.
Accordingly, many structural investigations have been performed on bulk and thin
film samples of SrTi03 . At the same time, many syntheses of SrTi03 nanoparticles
and nanowires have been reported. Despite these factors, however, the structure and
properties of SrTi03 nanoparticles and nanowires are not well understood. The aim
of this thesis is to better understand such SrTi03 nanoparticles and nanomaterials
using a combination of theoretical and experimental methods.
Density-functional calculations were performed of bulk SrTi03 and (100) SrTi03
surfaces, with a focus towards nanomaterials applications. The outer layers of both
SrO and Ti02 terminated (100) surfaces relaxed inward, and the subsequent layers
alternately moved outwards and inwards. Furthermore, surface rumpling was
observed. Both the interlayer distances and rumpling were determined as a function
of depth. Tests of different exchange-correlation functionals were performed
throughout.
Next, the first-ever density-functional calculations were performed of the structural
and electronic properties of SrTi03 nanowires. No ferroelectric states were found for
the nanowires, despite active searching. Compressive axial and lateral strain was
observed for all the nanowires, and the extent of this strain varied with diameter and
surface termination. Furthermore, surface rumpling was found to occur on and
within the nanowires; subsequent plots of the local polarization revealed that every
nanowire possessed a radial polarization texture. Finally, electronic band structure
calculations revealed that all the SrTi03 nanowires were metallic.
Finally, experimental studies were performed on SrTi03 nanoparticles, with the longterm
aim of determining and understanding their local atomic structure.
Transmission electron microscopy showed that the nanoparticles were polydisperse,
and powder x-ray diffraction measurements showed that they were composed of
mostly SrTi03.
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