Phase relations of the SrO-Ho2O3-CuOx system

The phase diagram of the SrO-R2O3-CuOx system, where R = Ho, was investigat ed in air. The tie-line relationships of the system were determined. The Sr analog of the high T-c superconductor Ba2HoCu3O6+x was not observed in thi s system. Two ternary phases were found, namely, the "14-24" solid solution Sr14-xHoxCu24O41 and the "green phase" SrHo2CuO5. Holmium was found to sub stitute for the Sr site in the solid solution Sr14-xHoxCu24O41 up to the va lue of x approximate to 5. The melting temperature range of this solid solu tion is from 975 to 1025 degrees C, for x = 0 to x = 5, respectively. The g reen phase is isostructural to its Ba analog, BaHo2CuO5, and is orthorhombi c with space group Pbnm and cell parameters a = 7.0971(13) Angstrom, b = 12 .0262(23) Angstrom, and c = 5.5849(12) Angstrom. A comparison of the Ho sys tem with reported systems of R = La, Nd, and Y indicated that a trend exist s. The larger the lanthanide ions, the more complicated the phase diagrams, i.e,, with a greater number of ternary phases/solid solutions. Despite sim ilar ionic radii between Ho3+ and Y3+, the phase diagrams of these two syst ems are rather different. The green phase SrHo2CuO5 is not stable in the Y system.