Synthesis and reaction route of bulk superconducting YBa2Cu4O8 and Y0.9Ca0.1Ba2Cu4O8 at normal oxygen pressure

An alternative method for preparing YBa2Cu4O8 and Y0.9Ca0.1Ba2Cu4O8 is described. The precursor was prepared by using spray drying and freeze drying techniques. The annealing process of YBa2Cu4O8 and Y0.9Ca0.1Ba2Cu4O8 was carried out at one atmosphere oxygen pressure,at 815 deg C. In every case the formation of an intermediate phase of the 1 2 3 phase was observed after the first sintering period of 50 h. The single 1 2 4 phase was obtained after another sintering process for 120 h. The formation of the intermediate 1 2 3 phase seems to be essential for producing the 1 2 4 phase. The results are discussed with respect to the thermodynamical stability of the individual compounds. 16 refs., 2 figs