*2.1. EDX*

We analyzed (Bi,Pb)-2212 samples with increasing concentrations of Zn, Y Nd, Ti, and the undoped reference sample. The chemical compositions have been obtained from the Energy Dispersive X-ray Spectroscopy (EDX) spectra shown in Figure 1. The spectra were collected in the energy range 0–40 KeV, nonetheless, no interesting features appeared above 20 KeV. The elemental contents per formula unit are reported in Table 1. In the first row, the composition of the undoped parent compound, named X000, is reported and taken as a reference; while in the following rows, the doping element of each sample is specified in the *'Dopant'* column. According to EDX analysis, the reference sample X000 has stoichiometry *Bi*1.74*Pb*0.39*Sr*1.75*Ca*0.73*Cu*2.39 *O*7.87, therefore it belongs to the 2212 phase *Bi*(<sup>2</sup>−*y*)*PbySr*2*CaCu*2*O*(<sup>8</sup>+*<sup>δ</sup>*), where y = 0.26 with some excess in Pb and Cu and deficiency in Sr and Ca. Assignment to the Bi-2212 phase is corroborated by the critical temperature T*c* = 75 K resulting from the Zero Field Cooling (ZFC) magnetization curve that is repeated in each panel of Figure 4 for a convenient comparison with doped samples.

All the samples have similar Pb substitutions on the Bi site, apart from sample Nd05 however, which is not superconductive (see below). Moreover, the off-stoichiometry of the other cations is of the same type as for the sample X000, apart from the Ti-doped samples. On the basis of the available data, it is difficult to further speculate on the site location of each substitution.

**Table 1.** Formula unit elemental composition of the analyzed samples according to Energy Dispersive X-ray Spectroscopy (EDX) analysis and corresponding critical temperature T*c* determined as the diamagnetic onset. The T*c* value marked with *'?'* is of uncertain determination because of the low intensity of the diamagnetic signal. The *'Mass'* column refers to the samples measured with the SQUID magnetometer.


**Figure 1.** EDX patterns for the analyzed samples. From top to bottom: Y, Zn, Ti, and Nd substitutions. In each panel, the black line is the pattern of the reference undoped sample X000. An enlarged view of this figure, with detailed type of each emission line, is available as Figure S1 in Supplementary Materials.

## *2.2. PXRD*

The quality of the products was also investigated by powder X-Ray diffraction (PXRD). The collected pattern of the reference sample X000 (black curve of Figure 2) matches the orthorhombic of the Bi-2212 phase (ICDD entry N.00-082-2278). A little amount of CuO is detected as the main spurious phase in all the patterns; this could explain the slight lack in composition detected for Cu by Energy Dispersive X-ray Spectroscopy (EDX) characterization. There are other traces of spurious peaks that are difficult to unambiguously address.

The Y and Zn series (see upper panels of Figure 2) do not affect the main phase stability, suggesting that Y and Zn easily substitute Ca—at least up to 0.5 in composition—within the structure. On the other hand, samples with the higher concentration of Nd and Ti (*x* 0.5–1) start to degrade the Bi-2212 phase, forming traces of spurious compounds (mixed Sr,Cu oxides). Interestingly, for Nd-substitution, the Bi-2212 phase is no longer superconducting for Nd ≥ 0.5, while in the case of Ti—in particular Ti10—the formation of higher member Bi-2223 phase was observed, in agreemen<sup>t</sup> with the double T*c* onset detected (Figure 4c)—the latter in the temperature range 104–108 K.

The effect of a heavy Y- and Nd-doping clearly leads to a large contraction of the cell along the (0 0 10) c-axis (much larger than for Zn and Ti); reversely, the b-axis slightly enlarges, more significantly for Nd than for Y substitutions, as shown in the PXRD patterns zoomed in the 2*θ* region 27–34.5◦, where the most intense and significative peaks are located for Y05, Nd05, and the reference sample X000 (Figure S3 in Supplementary Materials).

The simple one-to-one correlation between the crystallographic axes and the transition temperature T*c* does not account for the complexity of the HTS cuprates. Since their discovery, a massive experimental and theoretical effort has been focused to find which interatomic distances within the unit cell affect the superconductivity, with particular attention to the CuO2 planes aligned

along the c-axis of the highly anisotropic HTS cell, where the superconductivity actually takes place. The number, distance, and interlayer coupling of the CuO2 planes, their inner structure, *buckling angle*, in-plane cationic disorder, and the relation with the nonsuperconducting spacers were modified via cationic substitution. Despite the extensive work, the experimental results are still contradictory. In our case, the contraction of the c-axis of the heavily doped BSCCO samples is associated to the disappearance of the superconductivity in the Nd05 samples, and the drastic drop of the superconducting fraction in the Y05 one.

#### *2.3. SEM Morphology*

The surface morphologies observed by Scanning Electron Microscopy (SEM) images are reported in Figure 3. The reference sample features platelet-like grains of size in the order 10 *μ*, clearly depending on the synthesis/sintering procedures. The effect of doping on morphologies is of two opposite types, depending on the dopant element.

Moderate doping with Zn or Ti increases the size of platelets. Higher concentration of Ti, as in sample Ti10, induces a remarkably compact structure formed by merged layers and crossed by just few tubular cavities. Platelets' surface are clean, smooth, and the borders are neat.

**Figure 2.** Powder X-ray Diffraction (PXRD) patterns for the analyzed samples. From top to bottom: Y, Zn, Ti, and Nd substitutions. In each panel, the black line is the pattern of the reference undoped sample. Red bars: Bi-2212 pattern from ICDD (chart n.00-082-2278). Green bars: CuO impurity pattern. An enlarged view of this figure is available as Figure S2 in Supplementary Materials.

On the contrary, samples with Y and Nd show smaller flat flakes in the order of ∼2 μm, with size decreasing on increasing the dopant content and approaching a granular aspect ratio for sample Y05. Similar trends in the evolution of morphology have already been observed with other dopant species [11].

**Figure 3.** SEM surface micrographs of samples. From left to right, top to bottom: X000, Zn01, Zn05, Ti01, Ti05, Ti10, Nd01, Nd05, Nd10, Y01, Y05, as depicted in lower right corner.

#### *2.4. Magnetic Characterization*

In Figure 4, the resulting M(T) curves for reference and substituted samples are displayed. It is worth recalling that in a perfectly diamagnetic sample, the measured magnetic susceptibility is

$$\chi = \frac{-1}{4\pi(1-N)'} \tag{1}$$

where *N* is the demagnetizing factor along the magnetization direction. It is easy to realize that *N* plays an important role on the absolute value of the measured signal in superconducting materials. For example, two cylinders with aspect ratio height/diameter equal to 1 and 2 have demagnetizing factors 0.232 and 0.069, respectively [12]: substituting into Equation (1), one obtains a difference between the measured susceptibilities amounting to a remarkable 30%. Considering that our samples had different and irregular shapes, a rigorous quantitative comparison of their diamagnetic intensities would be of little meaning. Therefore, the numerical value of diamagnetic intensities will be taken into

account only in case of very notable differences between the samples, as in the case of Y substitutions. We will rather focus on estimating the critical temperatures T*c* that, in the M(T) curves, can be identified with the temperature of the diamagnetic onset.

**Figure 4.** Zero Field Cooling (ZFC) magnetization curves of doped samples measured in applied magnetic field H = 100 Oe. X000 reference sample is also shown in each panel for comparison. Panels clockwise from top left: (**a**) Zn, (**b**) Y, (**c**) Ti, and (**d**) Nd substitutions. Inset of panel (**a**): magnified vision highlighting the diamagnetic signal above T*c* of the Bi-2212 phase, suggesting the presence of a small fraction of Bi-2223 phase. Inset of panel (**d**): magnified vision of the paramagnetic signal of the nonsuperconductive samples Nd05 and Nd10.
