Synthesis and study of the ceramic high-T-c superconductor Hg1-xTlxBa2Ca1.8Y0.2Cu3O8+delta (x = 0.3, 0.5, 0.7, 0.9 and 1)

High-T-c superconducting ceramic samples of the form Hg(1-x)Tl(x)Ba(2)Ca(1. 8)Y(0.)2Cu(3)O(8+delta) (x = 0.3, 0.5, 0.7, 0.9 and 1) are prepared in a cl osed quartz tube at 860 degrees C. The electrical resistance versus tempera ture is measured in the temperature range between 15 K and room temperature . The effect of magnetic field and applied electric current on the second s tage of the transition is studied. It is found that the transition does not occur at a definite temperature but in a temperature range Delta T which m ay approach 50 K or even more. This is believed to be due to the very short coherence length (xi = 10 Angstrom) of HTSCs or to the random motion of th e magnetic flux. The results obtained in our work can give some information about superconducting grains and weak superconducting boundaries.