*2.1.1 Synthesis of Pr*2*Ba*4*Cu*7*O*<sup>15</sup>*<sup>δ</sup> samples*

First of all, flow chart of citrate pyrolysis technique for the synthesis of Pr2Ba4Cu7O15*<sup>δ</sup>* (sample #1) is illustrated in **Figure 3b**. We synthesized high-quality polycrystalline samples of Pr2Ba4Cu7O15*<sup>δ</sup>* by using a citrate pyrolysis technique [2, 3]. Stoichiometric quantities of high purity Pr6O11, Ba(NO3)2, and CuO were mixed and thoroughly ground. The mixture was dissolved in a nitric acid solution at 50–60°C. After adding citric acid to the resultant solution, we then neutralized it by adding aqueous

*(a) Typical crystal structure of double perovskite Ba*2*(Pr,Tb)(Bi,Sb)O*6*. (b) SEM image of Ba*2*TbBiO*<sup>6</sup> *polycrystalline film fabricated from the single-phase powders by an electrophoretic deposition technique. (c) Photograph of the pelletized precursors of Ba*2*TbBiO*<sup>6</sup> *after a citrate pyrolysis procedure.*

### **Figure 3.**

*(a)X-ray diffraction patterns of as-sintered polycrystalline Pr*2*Ba*4*Cu*7*O*<sup>15</sup>*<sup>δ</sup>. The (004) peak corresponds to one of typical Miller indexes of Pr247. The calculated curve is obtained using the lattice parameters in the text. Inset shows characteristic peaks at 2θ 7°, indicating the formation of Pr123, Pr124, and Pr247 phases. (b) Flow chart of citrate pyrolysis technique for the synthesis of Pr*2*Ba*4*Cu*7*O*<sup>15</sup>*<sup>δ</sup> (sample #1). After post-annealing of the as-sintered sample in a vacuum, quenching procedure is needed to obtain higher superconductivity due to further oxygen defects.*

*Functional Materials Synthesis and Physical Properties DOI: http://dx.doi.org/10.5772/intechopen.100241*

ammonia. After the solution was dried up under stirring on halogen lamp heater block, the porous black products were formed through the self-ignition process of it. Finally, the precursors were ground into fine powders and they were annealed under ambient pressure of flowing oxygen gas at 891°C 0*:*5°C for an extended period over 100120 h. For the present citrate pyrolysis synthesis procedure, we adopted the electric tube furnace with three zone temperature controlled system, to achieve the temperature uniformity within 1°C. In our previous study [26], we realized homogeneous distributions of the superconducting grains and improved weak links between their superconducting grains in the sintering procedure by using the 3 zone furnace. The oxygen in the as-sintered sample was removed by reduction treatment in a vacuum at 500600°C, yielding a superconducting material. In particular, sample #1 was quenched in air from 300°C down to room temperature and samples #2–1 and #2–2 were slowly cooled in the electric furnace, as listed in **Table 1**. As mentioned below, this quenching procedure is needed to obtain higher superconductivity due to further oxygen defects. Typical dimensions of the pelletized rectangular sample were <sup>4</sup> <sup>3</sup> 1 mm3 .
