Iron-based superconductors might be promising for high field applications due to their decent superconducting transition temperature Tc, high upper critical field and low anisotropy. However, similar to cuprates the materials suffer from the detrimental effect of large angle grain boundaries reducing significantly the critical current density J c. Therefore, a coated conductor technology must be applied to solve this issue using highly textured templates based either on the ion beam assisted deposition (IBAD) or the rolling assisted biaxial textured substrates (RABiTS) approach. The main aim of this thesis was to apply such templates and to study the correlation between the microstructure and the current transport on a local scale in epitaxial Fe(Se,Te) layers deposited on such tapes as well as on single crystals. Therefore, thin films were grown by pulsed laser deposition and studied in detail afterwards including a local texture analysis with high-resolution electron back scattering diffraction (EBSD) as well as transmission electron microscopy (TEM) to identify the local defect structure. Simultaneously, the current transport was investigated globally by magnetization measurements and on a local scale by scanning Hall probe microscopy (SHPM).
X-ray diffraction studies showed a clear epitaxial relationship and a high texture quality for thin films on all templates. However, misoriented grains were observed for higher deposition rates and film thicknesses. The Tc reached values of up to 21 K on CaF2 single crystals and 18 K on metal templates, respectively. The J c determined from magnetization loops showed values above 2 MA cm−2 and 1 MA cm−2 at 2 K in self-field on single crystals and IBAD based templates, respectively, whereas the global J c for films on RABiTS templates was one magnitude lower. Detailed TEM studies revealed smooth layers on all templates with minor defects for films on single crystals, but pronounced grain boundaries for layers on metallic templates.
Unfortunately, EBSD measurements on the grown films showed a low indexing rate prohibiting the analysis of the grain boundary network. In contrast, SHPM proved a homogeneous magnetization profile for Fe(Se,Te) films on singe crystals and IBAD templates, whereas a distinct magnetic granularity was observe on RABiTS tapes. Detailed TEM studies in combination with transmission Kikuchi diffraction pattern revealed a strong dependence of the film growth on the out-of-plane orientation of the Ni-W grains. In general, the local SHPM studies revealed a similar dependence of superconductivity on granularity for Fe(Se,Te) as previously observed for YBCO.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:85878 |
| Date | 09 June 2023 |
| Creators | Anna Thomas, Aleena |
| Contributors | Doert, Thomas, Nielsch, Kornelius, Klauss, Hans-Henning, Dresden University of Technology |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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