THE HIGH-PRESSURE SYNTHESIS, MICROSTRUCTURE AND SUPERCONDUCTIVITY OF INFINITE-LAYER (SR1-XPRX)CUO2

The infinite-layer (Sr1-xPrx)CuO2 superconductor has been synthesized under high pressure. It is found that the preparation conditions, espe cially the calcination temperature of the starting materials and the a nnealing temperature under high pressure, play a key role for obtainin g superconducting samples. The composition range in which superconduct ivity occurs in the (Sr1-xPrx)CuO2 samples is = 0.13-0.16. In this com position range, the sample with x = 0.14 shows the maximum transition temperature of T-c(onset) = 46 K and the normal-state resistivity of t he samples tends to change from semiconductor-like behaviour to metal- like behaviour with increasing Pr3+ doping content. The microstructure of the infinite-layer (Sr1-xPrx)CuO2 samples has been characterized b y SEM and TEM. From electron diffraction analysis, as well as EDAX com position analysis, it has been found that in addition to the main infi nite-layer phase, at least two impurity phases are present in the samp les. One is an Sr-rich impurity phase having a monoclinic structure wi th a = 4.8 Angstrom and c = 4.8 Angstrom. Antiphase domains have been observed in this phase. The other impurity has has an orthorhombic str ucture with a = 6.6 Angstrom, b = 5.7 Angstrom and c = 4.7 Angstrom.