Texture development in yttrium barium copper oxide films synthesized from metallo-organic precursors

Chandrasekaran Venkatraman, Purdue University

Abstract

The Metallo-Organic Decomposition technique has been utilized in the fabrication of $\rm YBa\sb2CU\sb3O\sb{7-\delta}$ films with preferred orientation on (100) MgO and (100) SrTiO$\sb3$ substrates. The development of preferred orientation in $\rm YBa\sb2Cu\sb3O\sb{7-\delta}$ films as affected by processing parameters such as precursor stoichiometry, film thickness, firing treatment and substrate surface characteristics was investigated. Results indicate that preferred orientation in $\rm YBa\sb2CU\sb3O\sb{7-\delta}$ films could be varied, with increasing film firing temperature, from c-axis fiber texture to near-CSL and cube-on-cube epitaxy. On cleaved (100) MgO substrates the degree of preferred orientation could be varied from broad fiber texture to an epitaxial orientation having an angular spread with a half maximum width of 6.4$\sp\circ$. Polishing the MgO substrates resulted in a decrease in the degree of preferred orientation to a distribution with a half maximum width of 20$\sp\circ$. Epitaxial growth was promoted by lattice matching on (100) SrTiO$\sb3$ substrates at lower film firing temperatures and exhibited a narrow orientation distribution (half maximum width of 2.5$\sp\circ$). A mechanism for the development of preferred orientation is proposed based on the microstructural and orientation observations. During the initial stages of firing, normal grain growth of the $\rm YBa\sb2Cu\sb3O\sb{7-\delta}$ phase from the amorphous precursor occurs. Natural growth anisotropy of the $\rm YBa\sb2CU\sb3O\sb{7-\delta}$ phase promotes fast (00l) in-plane growth during this stage. At higher firing temperatures, stability of certain substrate related orientations results in their growth at the expense of other orientations. The proposed mechanism is consistent with the epitaxial grain growth mechanism--a mechanism for the development of epitaxy in thin films by post-nucleation.

Degree

Ph.D.

Advisors

Liedl, Purdue University.

Subject Area

Materials science

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