A NEW FAMILY OF PB-BASED-1222 CUPRATES PB(SR,LA)(2)LN(2)CU(2)O(Z) (LN=GD, DY, EU, AND PR)

A series of new Pb-based 1222 cuprates of the general formula Pb(Sr,La )(2)Ln(2)Cu(2)O(z) (Ln=Gd, Dy, Eu, and Pr) has been reported in this p aper. In this kind of compounds, cations in the rock-salt-type monolay er completely consist of Pb ions, but the iodometric titration results indicate that the Pb ions in the rock-salt-type monolayer actually ex ist in the form of mixed valence states, i.e., Pb4+ and Pb2+, and the proportion of Pb4+ and Pb2+ is close to 1:1. The Pb-1222 phases Pb(Sr2 -xLax) Ln(2)Cu(2)O(z) are very sensitive to sintering temperature and atmosphere, as well as the Sr content. For example, pure Pb-1222 can b e only obtained at 920 degrees C in air for the composition Pb(Sr1.2La 0.8) Gd2Cu2Oz. All these Pb-1222 phases are not superconducting.