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.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:682183 |
| Date | January 2015 |
| Creators | Branfield, Thomas |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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