2.4.2. Y

Yttrium substitution is among the earliest attempted to achieve a T*c* increase in Bi-2212, finding the best doping value *x* = 0.1∼0.15 with corresponding T*c*∼ 92 K [13,14]; this has been attributed to the effect of Y3<sup>+</sup> substituting Ca2+, which compensates for the hole excess in *CuO*2 planes and restores the charge carrier concentration to its optimal value. As previously mentioned, in the literature, we did not find studies on Yttrium substitutions in (Bi,Pb)-2212, nonetheless, our measurements—panel (*b*) of Figure 4—show a similar effect on (Bi,Pb)-2212: sample Y01 (*x* = 0.17) confirms an increase in T*c* of about 20 K with respect to the undoped reference specimen X000; on the other hand, increasing Y content up to *x* = 0.64, as in sample Y05, the diamagnetic onset is restored to the undoped values. Moreover, the diamagnetic intensity at the lowest measured temperature drops from −0.178 emu/g of the undoped sample to −0.015 emu/g only of Y05. This fall is too important to be ascribed to the demagnetizing effect discussed in Section 2.4, as Equation (1) would lead to unrealistic demagnetizing factors, and points rather to a strong reduction of the superconductive volume fraction of the specimen. The latter feature is likely related to the weak connectivity of the granular morphology evidenced in Table 3.
