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Substitution reactions of TCNQ (7,7,8,8-tetracyanoquinodimethane) with suitable electron donor moieties extended the range of gamma-bridged adducts R(4)Q3CNQ and R(4)P3CNQ of which the short chain Z-beta-(l-butyl-4'-quinolinium)-alpha-cyano-4-styryldicyanomethanide (C[4]H[9](4)Q3CNQ) is a typical example. These zwitterionic D-pi-A materials (where D and A are electron donors and acceptors respectively) exhibit properties such as solvatochromism, molecular rectification and second harmonic generation. Further synthetic work concentrated on modifying the donor, the acceptor and the substitution position within these zwitterions to create a series of diverse materials for non-linear optic research. Modification of the picolinium and quinolinium systems where the TCNQ substitution is in the alpha-position, has created the extensive analogous series-R(2)Q3CNQ and R(2)P3CNQ, their properties being compared and contrasted to the original gamma-bridged adducts. The behaviour of the materials on the subphase and their resultant Langmuir-Blodgett (LB) film fabrication was studied. The abrupt change in molecular orientation in LB films of the gamma-bridged adducts occurring at R= C[15]H[31] and above was not seen in the more flatly orientated alpha-bridged adducts. Further characterisation of the LB films was performed using reflectance-absorption infrared spectroscopy (RAIRS) and surface plasmon resonance (SPR).A number of N-alkylpyridinium benzimidazolate betaine derivatives and the related betaine-TCNQ adducts were prepared and their LB film forming properties were studied.

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Made available in DSpace on 2014-10-09T12:36:44Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:05Z (GMT). No. of bitstreams: 1 04245.pdf: 2667747 bytes, checksum: 0d0a973c2b8011a3f767e65572ac2262 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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A method of performing accurate oxygen analysis on cuprate based superconducting materials was established using electron probe micro analysis (EPMA). A range of YBa₂Cu₃O_δ ceramics with varying oxygen concentration were used to test the method. Using YBCO as a reference material, a suitable standard for oxygen analysis of Bi₂Sr₂CaCu₂O_δ (BiSCCO-2212) materials was obtained. This standard was used to perform full elemental analysis of a range of BiSCCO-2212 crystals, post annealed in pO₂'s between 10^-5-2atm. When the average Cu valence of each crystal was calculated and plotted as a function of the critical temperature (T_c) for each crystal, it was shown that BiSCCO-2212 materials conformed to the 'universal' trend illustrated by most other HTS and did not exhibit anomalous behaviour as had been previously believed. The phase assemblage and superconducting properties of BiSCCO-2212 Ag-clad multifilamental wires, prepared using the powder-in-tube (PIT) method by BICC, were studied as a function of a time/temperature profile. pO₂ of the processing atmosphere was found to be the predominant factor in determining the stoichiometry of the 2212 phase within wires. The phase assemblage is not simply a function of pO₂ as previously believed and can be controlled, in part, by the post annealing temperature. Homogenisation of the phase assemblage in BiSCCO-2212 Ag-clad wires can be achieved by prolonged heating (96hrs) at an appropriate temperature. An investigation into the 10K superconducting BiSCCO phase has shown the Sr-rich solid solution to extend towards the ideal stoichiometry of 2:2:1 (Bi:Sr:Cu) with increasing pO₂. Using a combination of high pO₂ (60atm) to achieve the appropriate Bi:Sr stoichiometry followed by post annealing in N₂ to adjust the oxygen content, it was possible to prepare single-phase ceramics of stoichiometry Bi_2.11(2)Sr_1.90(2)Cu_0.99(2)O_δ with a T_c=10.5K(5).