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University of Wollongong

1. Li, Qi. Research on TFA-MOD derived YBa2Cu3O7-δ thin films on single crystal substrates: fabrication and second phase doping.

Degree: PhD, 2012, University of Wollongong

Yttrium barium copper oxide, a ceramic with the formula YBa2Cu3O7-δ (YBCO), is the first material into the superconducting state above 77 K, which means the low-cost liquid nitrogen can be used as coolant. Because YBCO not only has high critical transition temperature (Tc), but also has high irreversibility field (Hirr) and high critical current density (Jc), it has attracted enormous interest and efforts to make it realize real applications since being discovered in 1987. For most applications, such as the superconducting microwave filter, YBCO is usually required to be in an epitaxial film form, since biaxial texturing technology can minimize the weak-link effect at the grain boundaries to achieve high performance on current transport and related properties. In this work, a cost-competitive, easily scalable preparation route, the trifluoroacetate metal-organic deposition (TFA-MOD), was employed to fabricate undoped and doped YBCO thin films. There are two main focuses for the author’s own work in this thesis: I. Improvements of processing conditions to fabricate buffer layers and pure YBCO thin films on the selected single crystal substrates; II. Introduction of second phase into YBCO matrix, and research on the pining mechanisms of selected doped samples. The deposition of YBCO film on Al2O3 substrate can produce a promising device for microwave application; however, an appropriate buffer layer has to be inserted due to the diffusion of aluminum during heat treatment and the relatively large lattice mismatch between YBCO and Al2O3. In this work, pure (h00)-textured CeO2 buffer layers were deposited on single crystal r-plane Al2O3 (1-102) substrate by a hybrid process, which was combined with magnetron sputtering for the seed layer and metal-organic deposition for the subsequent layer. Strongly c-axis oriented YBCO films were deposited on the CeO2 buffered r-cut Al2O3 (1-102) substrates by means of the TFA-MOD method. Atomic force microscopy and scanning electronic microscopy results show that the prepared buffers and YBCO films are relatively dense and smooth. The critical current density of the YBCO films exceeds 1.6 MA/cm2 at 77 K, with a superconducting transition temperature of 90 K. The surface resistivity is as low as 14 µΩ at 1 GHz frequency. The flux pinning type of the derived film has been investigated by Dew-Hughes model. The results demonstrate that the hybrid route is a very promising method to prepare YBCO films for microwave application, which can combine the advantages of sputtering for preparing highly c-axis oriented CeO2 buffer layers and the advantages of metal-organic deposition with rapid processing, low cost, and easy preparation of large-area YBCO films. The next generation of wireless communication demands microwave filters with high bandwidth and low noise. Superconducting films epitaxially grown on some single crystal substrates are the most promising substitutes to replace the conventional copper filters. YBCO thin film and Al2O3 substrate make a good combination for…

Subjects/Keywords: YBCO; thin film; Ce02 buffer layer; chemical solution deposition (CSD); trifluoroacetate metal-organic deposition (TFA-MOD); second phase doping; pinning mechanism

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APA (6th Edition):

Li, Q. (2012). Research on TFA-MOD derived YBa2Cu3O7-δ thin films on single crystal substrates: fabrication and second phase doping. (Doctoral Dissertation). University of Wollongong. Retrieved from 020404 Electronic and Magnetic Properties of Condensed Matter; Superconductivity, 091201 Ceramics, 091205 Functional Materials ; https://ro.uow.edu.au/theses/3941

Chicago Manual of Style (16th Edition):

Li, Qi. “Research on TFA-MOD derived YBa2Cu3O7-δ thin films on single crystal substrates: fabrication and second phase doping.” 2012. Doctoral Dissertation, University of Wollongong. Accessed October 16, 2019. 020404 Electronic and Magnetic Properties of Condensed Matter; Superconductivity, 091201 Ceramics, 091205 Functional Materials ; https://ro.uow.edu.au/theses/3941.

MLA Handbook (7th Edition):

Li, Qi. “Research on TFA-MOD derived YBa2Cu3O7-δ thin films on single crystal substrates: fabrication and second phase doping.” 2012. Web. 16 Oct 2019.

Vancouver:

Li Q. Research on TFA-MOD derived YBa2Cu3O7-δ thin films on single crystal substrates: fabrication and second phase doping. [Internet] [Doctoral dissertation]. University of Wollongong; 2012. [cited 2019 Oct 16]. Available from: 020404 Electronic and Magnetic Properties of Condensed Matter; Superconductivity, 091201 Ceramics, 091205 Functional Materials ; https://ro.uow.edu.au/theses/3941.

Council of Science Editors:

Li Q. Research on TFA-MOD derived YBa2Cu3O7-δ thin films on single crystal substrates: fabrication and second phase doping. [Doctoral Dissertation]. University of Wollongong; 2012. Available from: 020404 Electronic and Magnetic Properties of Condensed Matter; Superconductivity, 091201 Ceramics, 091205 Functional Materials ; https://ro.uow.edu.au/theses/3941

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