Process for the preparation of a semiconductor from an oxalate

A process for the preparation of a phase-pure, copper-containing, ceramic oxide superconductor which contains, in addition to copper, at least one alkaline earth metal selected from the group consisting of Ba, Sr, and Ca, and at least one metal selected from the group consisting of Y, La, Tl, Pb and the rare earths, in which a solution is prepared which contains the soluble salts of these metals in the atomic ratios of the superconductor, the metals are precipitated as oxalates by combining this solution with an oxalic acid solution, the mixture of the oxalates is separated off, dried and decomposed to form the oxides, and the latter are subsequently sintered at temperatures of from 700.degree. to 900.degree. C. in the presence of oxygen and converted into the superconductor, which comprises carrying out the heating of the metal oxalate at 200.degree. to 400.degree. C. in a gas atmosphere which has an O.sub.2 partial pressure of from 0 to 5 mbar, and carrying out the heating of the oxide-containing powder formed therefrom up to 700.degree. C. in a gas atmosphere having an oxygen partial pressure from 1 to 50 mbar.