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SOL-GEL SYNTHESIS OF THIN CERAMIC BUFFER LAYERS FOR THE ‘COATED CONDUCTOR’ DESIGN

Veerle Cloet (UGent) , Jonas Feys (UGent) , Serge Hoste (UGent) and Isabel Van Driessche (UGent)
(2007)
Author
Organization
Abstract
The two main drawbacks in the production of large scale superconducting applications are the lack of flexibility of the ceramic YBa2Cu3O7-x superconductor and the absence of textured structure in bulk material. A solution to both problems is presented by the ‘coated conductor’ structure, which consists of a flexible metallic tape, covered with one or multiple thin ceramic buffer layers on which a superconducting film is deposited in the last stage. This research is concerned with the deposition of the buffer layers and their characterisation. A good buffer layer should have the following qualities: the layer must be thin (50-200 nm), the crystals must grow in a predefined direction along the c-axis, the surface must be smooth and no chemical interaction with the substrate or the superconducting layer should occur1. Many good buffer layers until today are produced using a vacuum technique, but this technique requires a lot of energy, is not easy upscalable and expensive. As an alternative, we present a non-vacuum technique based on the sol-gel method, which can be performed under atmospheric pressure and is moreover based on less expensive metal salts dissolved in water or organic solvent. The two types of buffer layers, presented in this work, are CeO2 and La2Zr2O7. The precursor solution for the CeO2 layer, consists of cerium acetate dissolved in organic solvents2. The La2Zr2O7 (LZO) precursor is made of lanthanum(III)acetate and zirconium(IV)acetate hydroxide dissolved in water. To ensure that the metal ions are built in in a complex and have no possibility to precipitate as a hydroxide compound, triethanolamine is added as a complexing agent. In both cases, evaporating the solvent will transform the solution into a gel, in which the metal complexes are dispersed homogeneously3. With these precursor solutions, a thin layer is deposited on the Ni-5at% W tape by the dip-coating process. To finalise the synthesis, a heat treatment at elevated temperatures (1050°C) will convert the amorphous gel into a crystalline thin film. Characterisation of the film was done by X-ray diffraction, pole figures, SEM, AFM, FIB and TEM. Crystallographic analysis has shown that the crystals are well oriented according to the c-axis and show good in- and out-of-plane orientation. The surface is crack-free but shows small pores and nucleation sites, which makes the surface rough. Cross-section in FIB and TEM has revealed a thickness of 25-40 nm for the CeO2 layer and 65-80 nm for the LZO layer.

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Chicago
Cloet, Veerle, Jonas Feys, Serge Hoste, and Isabel Van Driessche. 2007. “SOL-GEL SYNTHESIS OF THIN CERAMIC BUFFER LAYERS FOR THE ‘COATED CONDUCTOR’ DESIGN.” In .
APA
Cloet, V., Feys, J., Hoste, S., & Van Driessche, I. (2007). SOL-GEL SYNTHESIS OF THIN CERAMIC BUFFER LAYERS FOR THE “COATED CONDUCTOR” DESIGN. Presented at the Doctoraatssymposium.
Vancouver
1.
Cloet V, Feys J, Hoste S, Van Driessche I. SOL-GEL SYNTHESIS OF THIN CERAMIC BUFFER LAYERS FOR THE “COATED CONDUCTOR” DESIGN. 2007.
MLA
Cloet, Veerle, Jonas Feys, Serge Hoste, et al. “SOL-GEL SYNTHESIS OF THIN CERAMIC BUFFER LAYERS FOR THE ‘COATED CONDUCTOR’ DESIGN.” 2007. Print.
@inproceedings{598605,
  abstract     = {The two main drawbacks in the production of large scale superconducting applications are the lack of flexibility of the ceramic YBa2Cu3O7-x superconductor and the absence of textured structure in bulk material. A solution to both problems is presented by the ‘coated conductor’ structure, which consists of a flexible metallic tape, covered with one or multiple thin ceramic buffer layers on which a superconducting film is deposited in the last stage. This research is concerned with the deposition of the buffer layers and their characterisation. A good buffer layer should have the following qualities: the layer must be thin (50-200 nm), the crystals must grow in a predefined direction along the c-axis, the surface must be smooth and no chemical interaction with the substrate or the superconducting layer should occur1. 
Many good buffer layers until today are produced using a vacuum technique, but this technique requires a lot of energy, is not easy upscalable and expensive. As an alternative, we present a non-vacuum technique based on the sol-gel method, which can be performed under atmospheric pressure and is moreover based on less expensive metal salts dissolved in water or organic solvent. 
The two types of buffer layers, presented in this work, are CeO2 and La2Zr2O7. The precursor solution for the CeO2 layer, consists of cerium acetate dissolved in organic solvents2. The La2Zr2O7 (LZO) precursor is made of lanthanum(III)acetate and zirconium(IV)acetate hydroxide dissolved in water. To ensure that the metal ions are built in in a complex and have no possibility to precipitate as a hydroxide compound, triethanolamine is added as a complexing agent. In both cases, evaporating the solvent will transform the solution into a gel, in which the metal complexes are dispersed homogeneously3. 
With these precursor solutions, a thin layer is deposited on the Ni-5at% W tape by the dip-coating process. To finalise the synthesis, a heat treatment at elevated temperatures (1050°C) will convert the amorphous gel into a crystalline thin film. 
Characterisation of the film was done by X-ray diffraction, pole figures, SEM, AFM, FIB and TEM. Crystallographic analysis has shown that the crystals are well oriented according to the c-axis and show good in- and out-of-plane orientation. The surface is crack-free but shows small pores and nucleation sites, which makes the surface rough. Cross-section in FIB and TEM has revealed a thickness of 25-40 nm for the CeO2 layer and  65-80 nm for the LZO layer.},
  author       = {Cloet, Veerle and Feys, Jonas and Hoste, Serge and Van Driessche, Isabel},
  language     = {eng},
  location     = {Gent},
  title        = {SOL-GEL SYNTHESIS OF THIN CERAMIC BUFFER LAYERS FOR THE ‘COATED CONDUCTOR’ DESIGN},
  year         = {2007},
}