• Daniel Homa

      Articles written in Bulletin of Materials Science

    • Optical, mechanical and TEM assessment of titania-doped Bi2V1−𝑥Ti𝑥O$_{5.5−\delta}$ bismuth vanadate oxides

      Gurbinder Kaur Gary Pickrell Vishal Kumar Om Prakash Pandey Kulvir Singh Daniel Homa

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      Optical, mechanical and structural behaviors have been studied for titania-doped Bi2V1−𝑥Ti𝑥O$_{5.5−\delta}$ which are used as electrolytes for intermediate temperature fuel cells. Parameters like band gap ($E_{g}$), Urbach energy ($E_{u}$), refractive index, hardness (𝐻) and fracture strength (𝐾) have been calculated as a function of dopant concentration, i.e. 0.05 ≤ 𝑥 ≤ 0.2. Furthermore, analysis of transmission electron microscopy (TEM) images for all the oxides was conducted along with line spectra of planes. Results are discussed in light of correlation of these optical and mechanical parameters to their structural properties. Band gap has also been correlated to the conductivity of these oxides. Good correlation has been obtained between them.

    • Reaction of YBa$_2$Cu$_3$O$_{7−x}$ (YBCO) and fused silica in YBCO glass fibres

      HANNA HEYL DANIEL HOMA GARY PICKRELL

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      This work introduces the first reported experiments on drawing YBa$_2$Cu$_3$O$_{7−x}$ (YBCO) into fibres with a fused silica cladding using a fibre draw tower to manufacture YBCO glass fibres. These fibre draw experiments allowed manufacturing fibre sections with core diameters between 50 and 200 $\mu$m and a length of around 1.2 m. However, reactionsbetween the fused silica cladding and the YBCO core were revealed by the fibre drawing process. Therefore, this study focusses on investigating these reactions (in as-drawn fibres as well as after additional heat-treatments) using energy dispersive spectroscopy analyses on an environmental scanning electron microscope as well as using X-ray photoelectron spectroscopyanalyses and a cross-polarized light study. The results showed the formation of silica precipitations inside the as-drawn YBCO core, forming an interface layer between the core and the cladding regions, as well as the presence of a high silicon content inside the core with a possible silicate formation. Additional heat-treatments have shown the formation of silica and copper oxide co-precipitations at 900$^{\circ}$C. In addition, heat-treatments at higher temperatures have shown the occurrence of further reactions, which led to a degradation of the core and the formation of new phases.

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