Formation and superconductivity of Pr and Nd-substituted Tl-1212 phase (Tl0 .85Cr0.15)Sr2CaCu2O7

The derivatives of Tl-1212 type phase superconductors with nominal starting compositions (Tl0.85Cr0.15)Sr-2 (Ca1-xRx) Cu2O7 where R = Pr or Nd (Ca ser ies) together with (Tl0.85Cr0.15)Sr-2 (Sr1-xPrx)Cu2O7 (Sr series) for x = 0 -0.5 have been prepared and investigated by d.c. electrical resistance and powder X-ray diffraction analyses. Partial substitution of Ca with Pr or Nd has the advantage of stabilizing the tetragonal phase with space group P4/ mmm but suppressed the onset critical temperature T-c onset. The Ca series generally showed a higher T-c onset than the Sr series. The importance of i onic radius of the substituted elements and the effects of starting composi tion on T-c onset and phase formation are discussed.