DERIVATIVES OF TLSR2CACU2O7 FROM ELEMENTAL SUBSTITUTIONS OF PB FOR TL, LA FOR SR, AND Y FOR CA

Tl(Sr,La)2CaCu2O7, Tl(Sr,La)2(Ca,Y)Cu2O7, and (Tl,Pb)(Sr,La)2(Ca,Y)Cu2O7 were synthesized and characterized. Thus, all derivatives of the 1212-type phase TlSr2CaCu2O7 from elemental substitutions, Pb for Tl, La for Sr, or/and Y for Ca, have been synthesized. La and Y play a similar role in the substitutions. Pb is necessary to increase the Tc from 90 K to above 100 K in the double substitutions while it plays a role similar to La and Y in the single substitution. The triple substitution of Pb, La, and Y does not increase Tc to even higher. The optimal average Cu valence is 2.20 +/- 0.05, the same for all derivatives.