Effects of Sr substitution on T-c of Y0.85Ca0.15Ba2-xSrxCu3Oy

We have studied the Ar annealing effect on T-c of Y0.55Ca0.15Ba2-xSrxCu3Oy (x = 0.0, 0.5 and 1.0) samples. Ar annealing was carried out at 480 degrees C for 15 min similar to 10 h. As the annealing time increases, T-c of the x = 0.0 and 0.5 samples first gradually increases to a maximum value, then i t decreases slowly suggesting the assintered samples are in the over-doped state. However, the x = 1.0 sample shows an anomalous behavior. T-c increas es from 68 K to 75 K after Ar annealing for 15 similar to 30 min, then it a bruptly decreases to 40-50 K after further Ar annealing.