Growth and characterisation of textured superconducting tapes

Al Khateeb, Shadi Mohammad Abdel Kareem (2009). Growth and characterisation of textured superconducting tapes. University of Birmingham. Ph.D.

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Abstract

MgO thin films were deposited on Si (100) single crystals, NiW tapes, 310 austenitic stainless steel and Hastelloy C276 by the ultrasonic Spray Pyrolysis technique, using magnesium nitrate and magnesium acetate as precursors at many different conditions. Thermogravimetrical analysis (TGA) of the decomposition of the precursors was used as a guideline temperature for the thin film deposition. Biaxially textured and epitaxial MgO films were deposited on Si substrates using magnesium nitrate precursors. An amorphous MgO thin film was deposited on NiW tapes, NiO buffered NiW, 310-stainless steel and Hastelloy C276 when using low concentration of the magnesium nitrate precursor. Higher concentrations were needed to obtain (200) oriented MgO films on C276. However, NiW tapes and 310-stainless steel were found to be a non suitable substrate for MgO thin film deposition due to surface instability. A (200) oriented MgO thin film was grown on Hastelloy C276 using a magnesium acetate precursor at a much lower concentration compared to the nitrate precursor. The ISD deposition by spray pyrolysis (irrespective of the used precursor and the used substrate) produced MgO films that grew with the (200) normal to substrate surface as distinct to MgO films grown by thermal evaporation which grew with the (200) tilted to the substrate normal. Pulsed laser deposition (PLD) was used to deposit YBCO on MgO buffered substrates. The characterization of the thin films was done using SEM, EBSD, XPS, AFM, X-ray diffraction 2-scans, rocking curve (-scans), phi () scans, X-ray pole-figure measurements, and AC susceptibility. YBCO deposition by PLD on Si substrates buffered with MgO was not successful due to the thermal stresses developed in the MgO buffer. An EDX line scan performed on MgO films deposited on Hastelloy C276 from the acetate precursors confirmed the effectiveness of such layer as a diffusion barrier. It was found that c-axis oriented YBCO films were grown on c axis oriented MgO films deposited on C276 from the nitrate and acetate precursors; however, MgO and YBCO films have a very weak in-plane texture. The AC susceptibility measurements show that the YBCO films have a broad superconducting transition temperature irrespective of the precursor used. To improve the superconducting transition temperatures, different annealing treatments were performed on the MgO buffer deposited on Hastelloy C276, however, it was found that the as deposited MgO buffer films and subsequent deposition of YBCO films gave the best superconducting transition temperatures. In an attempt to improve the in-plane texture of YBCO, CeO2 was deposited by PLD on the spray pyrolysed MgO.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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