The Pr(Ba1-xPrx)(2)Cu3O7+delta solid solution. A crystal structure and phase diagram study

Samples of nominal composition Pr(Ba1-xPrx)(2)Cu3O7+delta with -0.15 less t han or equal to x less than or equal to 0.6 and Nd(Ba0.6Nd0.4)(2)Cu3O7+delt a were characterized by X-ray powder diffraction combined with Rietveld ana lysis, differential thermal analysis (DTA), thermogravimetry (TG), and AC s usceptibility measurements. Pr(Ba1-xPrx)(2)Cu3O7+delta is formed by the per itectic reaction Pr2CuO4 + L --> Pr(Ba1-xPrx)(2)Cu3O7+delta at 1060 +/- 10 degrees C with x approximate to 0.35 and the homogeneity range extends from x approximate to 0.06 at 975 +/- 10 degrees C to x approximate to 0.45 at 1012 +/- 10 degrees C which is consistent with the X-ray diffraction result s. As for the Nd(Ba1-xNdx)(2)Cu3O7+delta solid solution, three distinct dom ains were found. In the Ba-rich region (0 < x < 0.15), the structure is tet ragonal or orthorhombic depending on oxygen content. On the contrary, the s tructure of the 1212 phase is always tetragonal in the intermediate region (0.15 less than or equal to x less than or equal to 0.30) and always orthor hombic in the Pr-rich region (0.30 < x less than or equal to 0.45). In addi tion, the composition range with respect to oxygen is significantly reduced compared to RBa2Cu3O7-delta. The transition from the tetragonal intermedia te domain to the orthorhombic Pr-rich domain results in the expected eightf old coordination for Pr atoms on Ba site when the Pr/Ba ratio for this site approaches unity. No evidence of a superstructure was found for either Pr- or Nd-containing 1212 phases. (C) 1999 Elsevier Science B.V. All rights re served.