Process for producing thick-film tape-shaped re-type (123) superconductor

#This invention relates to a process for producing an oxide superconductor. In particular, this invention relates to the process for producing thick-film tape-shaped RE-type (123) superconductor which is useful to a superconducting magnet, a superconducting electric power cable, an electric power device, etc.

#About the oxide superconductor, because that critical temperature (Tc) exceeds the liquid nitrogen temperature, the applications for the superconducting magnet, the superconducting electric power cable and the electric power device, etc. are expected, and the various studies are advanced vigorously.

#In order to apply the oxide superconducting wire to the above mentioned field, it is necessary to produce a long wire which has a high critical current density (Jc) and a high critical current value (Ic). On the other hand, in order to obtain a long tape, it is necessary to form the oxide superconductor onto a metallic tape shaped substrate from viewpoint of strength and flexibility. Also, in order to enable use of the oxide superconductor at a practical level which is equivalent to the metallic superconductor such as Nb3Sn or Nb3Al, the Ic value of about 500 A/cm (at 77K, in self-field) is required.

#[FIG. 1] The drawing which shows the relation between the water vapor molar fraction XH2O and the growth rate of YBCO crystal.

#[FIG. 2] The drawing which shows the relation between the vapor partial pressure PH2O and the Jc value.

#[FIG. 3] The drawing which shows the relation between the crack occurrence and the vapor partial pressure in each film thickness of YBCO superconducting film produced by the conventional process.

#As described above, this invention has the main feature that the intermediate heat-treatment is given with the low temperature than the heat-treatment temperature for producing the superconductor between the calcination heat-treatment and the heat-treatment for producing the superconductor.

#Besides, it is preferable that the above described intermediate heat-treatment is given at temperature in the range of 350-750 degrees C., and that the calcination heat-treatment is given at low temperature than the heat-treatment temperature of this intermediate heat-treatment. In addition, it is preferable that this intermediate heat-treatment is given in the mixed gas atmosphere which includes water vapor and oxygen in the gas which does not react to the RE-type (123) superconductor. However, it is possible that the intermediate heat-treatment is given also in oxygen, argon or air. In the case of adopting the mixed gas atmosphere, it is preferable that the oxygen partial pressure is 1% or less.

#In this invention, the effectiveness is brought out more by adopting TFA-MOD process. As the raw material solution in this case, the mixed solution of the organic solvent and the metal organic acid salt is used. For example, the metal organic acid salt is any one or more kinds of metal salt having carboxyl group, amines metallic salt having amino group, amino acid metallic salt comprising amino group and carboxyl group, nitrate, metallic alkoxide and acetylacetonate. Especially, the mixed solution including any one or more kinds of trifluoroacetate, naphthenate, octylic acid salt, neodecanoic acid salt, isononanoic acid salt is used. In this case, as the raw material solution, it is preferable to use the mixed solution comprising the organic solvent and the metal organic acid salt including the fluorine.