Method of preparing YBa.sub.2 Cu.sub.3 O.sub.7 powder for forming by drawing-lamination

A method of preparing a powder of YBa.sub.2 Cu.sub.3 O.sub.7 suitable for forming by drawing-lamination, which method comprises:

• preparing a powdered reactive mixture of precursors of purity greater than 99% and comprising Y, Ba and Cu such that the overall stoichiometry of the mixture is YBa.sub.2 CU.sub.3 accurate to less than 1%,
• binding said powdered reactive mixture to form intermediate pieces less than two millimeters in thickness which are placed in contact with a support in an oven so that their contact area with the support is small and liquid phase which appears during subsequent heat treating of said intermediate pieces is therefore preserved since it has little risk of being absorbed by the support,
• heat treating said intermediate pieces in said oven such that said heat treating comprises at least the following stages:
• a first dwell of duration in the range of 10 hours to 30 hours at a temperature, T.sub.1, in the range 890.degree. C. to 910.degree. C. in an atmosphere of 20% oxygen, corresponding to synthesis of the quadratic phase of YBa.sub.2 Cu.sub.3 O.sub.7,
• a second dwell of duration in the range 20 hours to 100 hours at a temperature, T.sub.2, in the range 920.degree. C. to 960.degree. C. in an atmosphere of 20% oxygen, corresponding to re-crystallization of the quadratic phase of YBa.sub.2 Cu.sub.3 O.sub.7, and
• a third dwell of duration in the range 10 hours to 50 hours at a temperature, T.sub.3, in the range 500.degree. C. to 300.degree. C. in a pure oxygen atmosphere, corresponding to transformation of the quadratic phase of YBa.sub.2 Cu.sub.3 O.sub.7 into the orthorhomic phase of YBa.sub.2 Cu.sub.3 O.sub.7, and
• dry grinding said heat treated intermediate pieces to obtain grains of said powder with an average diameter of the order of a few .mu.m.