**1. Introduction**

Bismuth-based cuprates (BSCCO) were the first discovered high-temperature superconducting materials with no rare earth content [1]. Their crystal structure is formed by superconducting *CuO*2 planes separated by charge reservoir layers crystallizing according to the general formula *Bi*2*Sr*2*Ca*(*<sup>n</sup>*−<sup>1</sup>)*CunO*(<sup>2</sup>*n*+4+*<sup>δ</sup>*), where *n* is the number of *CuO*2 planes in the unit cell. The superconducting phases occur at *n* = 1 (Bi-2201, T*c* = 10 K), *n* = 2 (Bi-2212, T*c* = 85 K), and *n* = 3 (Bi-2223, T*c* = 110 K). While the highest T*c* value pertains to Bi-2223, the most studied phase is Bi-2212 because of its higher thermodynamic stability and easier production route [2].

The superconducting properties of BSCCO systems—similarly to the other high-temperature superconductor (HTS) cuprates—depend on the charge-carrier concentration in the *CuO*2 planes, which in turn is strongly affected by off-stoichiometricity. In particular, between oxygen excess and cationic disorder, the latter plays a dominant role [3]. With regard to this, it should be remarked that exact stoichiometries are extremely difficult to obtain in bulk compounds since, along with the starting composition, the sintering and processing conditions may affect the formation and amount of extra phases [4] or members of the homologous series with higher *n* values among the final results. Besides, an analysis of the ionic radii sizes shows that replacement of Ca,Sr with Pb,Cu is possible in presence of Cu<sup>+</sup> ions, with suitable *δ* values to preserve charge balance. Pb doping has been found long since [5] to yield favorable improvements: substituting Bi3<sup>+</sup> with Pb2<sup>+</sup> increases the formal Cu valency and thus the number of hole charge carriers [6], as a result, one has a sizable increase in the critical current *Jc*(*H*) under magnetic field at optimal Pb content x = 0.16 with no significant variation in T*c* [7]. For this reason, most of the currently produced BSCCO compounds belong to the Pb-doped family (Bi,Pb)-2212, and much research effort is aimed at finding other substitutions in search of further improvements.

In this study, we investigate the effect on the superconducting and structural/morphological properties of Zn, Y, Ti, and Nd substitutions in (Bi,Pb)-2212 up to high dopant concentrations. Whilst to the best of our knowledge, there are no studies reporting on the yttrium substitutions in (Bi,Pb)-2212, earlier studies on Zn-, Ti-, and Nd-substituted (Bi,Pb)-2212 are available for concentrations up to 0.04 [8], 0.15 [9], and 0.50 [10], respectively. In this work, we extend the investigated values to 0.32, 0.67, and 0.67.
