Magnetic pair breaking by the Pr ions in the two “RE-123” EuBa2Cu3O7−δ and ErBa2Cu3O7−δ HTSCs codoped with Ca

The suppression of superconductivity by the equal substitution of Pr and Ca into the Eu and Er “123” HTSCs are studied. The decreases in the Tcs of Eu1−2xPrxCaxBa2Cu3O7−δ and Er1−2xPrxCaxBa2Cu3O7−δ are observed to be linear as x increases from 0.0 to 0.010. The rate of suppression dTc/dx for the “Eu-(Pr,Ca)-123” HTCSs is larger than that for the “Er-(Pr,Ca)-123” HTSCs. It is observed that in the specimens studied, the Cu valencies (reflecting the hole concentration) for each of the doped specimen in the two series remain almost constant. This points to the suppression of superconductivity in the present “123” HTSCs by Pr substitution being due to magnetic pair breaking by the Pr ions. The relative magnitudes of the rates of suppression of the two systems and the of the Tcs of the host superconductors are taken to be manifestation of an rare earth size effect.