Evidence of hole filling or hybridization in Y1−xPrxBa2Cu3O7−δ and Nd1>−xCexBa2Cu3O7−δ thin films

Superconductivity in PrBa2Cu3O7: Implications

“…The exceptions among the 123-compounds have been especially interesting, with Pr123 being the most thoroughly studied; they are: (i) Pm123 has not been fabricated because Pm is radioactive; (ii) Tb123 does not form with conventional fabrication methods, but Y 1−y Tb y 123 forms for y < 0.5 and superconducts at ≈ 90 K for these compositions y, indicating that Tb123 very likely would superconduct if it formed; 2 (iii) Ce123 does not form either, but Nd 1−y Ce y 123 does 3 and T c (apparently) decreases roughly linearly with increasing y, a behavior similar to that observed for Y 1−y Pr y 123; 3,4 (iv) Cm123, with actinide Cm, (apparently) does not superconduct, 5 despite Cm +3 being isoelectronic to Gd +3 (Gd123 superconducts at ≈ 90 K); and (v) Pr123 had not superconducted until recent attempts to test theoretical predictions 6 that it must superconduct were successful. [7][8][9][10][11][12][13][14] Until 1994, most workers believed Pr123 to be an insulator, 15 a position that was difficult to reconcile with the evidence that the similar material PrBa 2 Cu 4 O 8 (Pr124) (with a second Cu-O chain-layer in every unit cell) was thought to be an intrinsic metal that did not superconduct.…”

Superconducting and Electrotransport Properties of Y0.89R0. 11Ba2Cu3O7−δ (R=La, Pr) Polycrystals

“…Thus, the ionic radius of La is greater than that of Pr and the valency is 3, while Pr exhibits a mixed valence of 3 and 4. However, the tetravalent (Pr 4+ ) ion, compared to the trivalent (Pr 3+ ), has a smaller radius, which is very close to the radius of Y 3+ and can easily substitute it [5,7,8,12].…”

“…It was found that the nature of the change in the critical and structural characteristics of the Y 1−x R x Ba 2 Cu 3 O y compound largely depends on the ionic radius of R, its concentration (x) and valence [1,3,4,[6][7][8][9][10]. Thus, among the R elements that replace Y, it is particularly important to study the effects of Pr and La in Y-123, because the first of them can appear in both trivalent and tetravalent states, and the second only in trivalent [1,5,[10][11][12]. In addition, the ionic radius of La is larger than the ionic radii corresponding to the two valence states of Pr.…”

FLUCTUATION-INDUCED CONDUCTIVITY OF POLYCRYSTALLINE Er1-xTbxBa2Cu3O7-δ SUPERCONDUCTORS

“…The substitution of Y by trivalent rare earth (RE) elements in YBa 2 Cu 3 O 7−δ (YBCO) yields a superconducting phase with a critical temperature (T C ) identical to YBCO [1][2], except for Ce, Tb and Pr. For higher concentrations, Ce and Tb do not replace Y to form a single phase material from the standard solid state reaction technique [3][4], leading to the formation of multiphase samples, with BaCeO 3 and BaCu 2 always present [5][6]. PrBa 2 Cu 3 O 7−δ (PBCO) is isostructural to YBa 2 Cu 3 O 7−δ , but is still not superconducting [7].…”