Dunnill, Charles W. H.
Synthesis, characterisation and properties of tantalum based inorganic nanofibres.
PhD thesis, University of Glasgow.
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This thesis describes the synthesis and characterisation of 1-dimensional nanometric phases using simple preparative reactions and a variety of characterisation methods. Comparison of properties between the bulk and nano-morphology has played a large part and is a common theme throughout.
High aspect ratio tantalum disulfide, TaS2 nanofibres were prepared from a 1:2 stoichiometric mixture of elemental powders in a one-step synthesis utilising silica ampoules. A surface assisted growth phenomena was investigated and found to significantly increase the yield, both in quality and quantity. The resulting nanofibres were seen to retain and indeed enhance some of the bulk properties, e.g. a 50 fold increase in observed superconducting transition temperature.
Changing the stoichiometry of the reactants to 1:3, produced tantalum trisulfide nanofibres. Tantalum trisulfide is of interest as it has pseudo 1-dimensional crystal structure and properties in the bulk. TEM and SAED have shown that the TaS3 unit cell is oriented with the b direction parallel to the long axis of the nanofibres, indicating the potential for the transfer of the low dimensional properties of the bulk material into the nanophase morphology. (Low dimensional properties of bulk TaS3 result from chains of tantalum atoms propagating along the b direction of the unit cell). Although the structure of the TaS3 remains illusive the preliminary investigations show these nanofibres to be metallic along their lengths, potentially leading to many applications in nanoscale electrical devices.
The concept of pseudomorphic change from the disulfide nanomaterials into more functional materials such as Ta3N5 and Ta2O5 was investigated. Nanofibres were initially formed and can reversibly be inter-converted between the three different nanometric phases (TaS2, Ta3N5 and Ta2O5) using simple solid-gas reaction, without significant loss of nanofibrous morphology. Further this series of reactions shows potential for the formation of other related and potentially applicable nanometric phases such as TaN, TaO2 and TaON as well as opening the door to countless other analogous systems.
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