Required Crack-Preventing Chemicals and Chemical Background for Single-Coated Technology to YBCO Thick Films by TFA-MOD

Single-coating technology for metal-organic deposition using trifluoroacetate (TFA-MOD) is indispensable, because single-coated film has no intermediate layer that causes fatal deterioration in superconducting properties. This technology requires a crack-preventing chemical (CPC). Our group reported several CPCs at ASC2008. With the CPCs, we obtained single-coated thick films with thickness of over 1 micrometer. Some CPCs cause crack formation and increase carbon and fluorine residues in the resulting superconducting films. The objective of this study is to discover CPCs that cause no crack formation. Our study concludes that CPCs for TFA-MOD must have the following attributes: no branch structure, no ether bonds, no chemical double bonds in the carbon chain, strong acidity (pH -1 to 1), -(CF₂)- chain, and hydrogen terminations. Among more than 1 000 000 organic chemicals, there are only two series of chemical groups that work effectively as CPCs in TFA-MOD : H-(CF₂)_n-COOH and HOCO-(CF₂)_n-COOH.