Reactivity between Nd_1 xBa_2 xCu₃O_7   x/2and Nd_4 2zBa_2 2zCu_2 zO_10 2zphases in superconducting NdBaCuO powders and melt textured bulk samples

Abstract

The high temperature reaction between the superconducting Nd123(x) (Nd 1+x Ba 2−x Cu 3 O 7−δ+x/2 ) phase and Nd422(z) (Nd 4−2z Ba 2+2z Cu 2−z O 10−2z ), leading to substitutions of Nd in the Ba sites of Nd123, was analysed. For this purpose, differential thermal analysis (DTA) was performed on powders with different Nd422 addition. Measurement results were compared with the values, reported in the literature, of the peritectic temperatures in function of Nd123 substitution. The superconducting transition critical temperature analysis of melt-textured samples shows that the use of Barium rich Nd422 allows significant improvements of the superconducting parameters of produced samples, avoiding the occurrence of the Nd-Ba substitutions.

Thermochemistry of Nd4−2xBa2+2xCu2Oz (x=0, 0.1)

“…The existence of the solid solution Nd 4−2x Ba 2+x Cu 2 O z (x = 0-0.2) with a certain range of homogeneity was reported in [2,3]. In order to investigate the cation nonstoichiometry we prepared a series of solid solutions in steps of x = 0.05.…”

Mechanical Fragility and Tri-Dimensional Crack Structure in NdBaCuO Top Seeded and Multi-Seeded Melt-Textured Samples

“…The presence of the highly reactive Nd163 phase [15] (product of Nd123-Nd210 reaction) is supposed not to play any important role in the crack formation process, due to Nd163 rapid decomposition into Nd123 and oxides. Precursors characterized by such a high barium contents (Nd210 and Nd422(0.2)) were used to minimize the occurrence of cationic substitution in Nd123 as better illustrated elsewhere [9], [10], [16].…”

“…The binary oxides , CuO and were mixed in the stoichiometric amounts by ball-milling, and then repeatedly calcinated until completion of the reaction as reported elsewhere [9], [16]. After that, powders mixture in the desired molar ratio were ball milled during 2 h.…”

A simple statistical phenomenological model for cation substitutions in Nd1+xBa2−xCu3O7−δ+x/2

“…In the following we will use for the values of the extremes, data taken by Goodilin et al [10] and (for T = 890°C) by Yoo and McCallum [1], (x min =0.04 and x max =0.6). For Nd422 the experimentally determined extremes at 890°C [11] are -0.12<z<0.13 (the formula used for Nd422(z) in [11] is different from Eq.2, although equivalent to it [12], so we have converted the results). The appearance of substituted phases has been observed in all processes involving Nd123, such as powder synthesis, film deposition, sintering, melt texturing etc.…”

“…Particularly complex is the case of melt texturing techniques, in which Nd422(z) is added to Nd123 powders. In this case, they react following the reaction [12]: 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 …”