Phase Relations of the SrO–Ho2O3–CuOx System

The phase diagram of the SrO–R2O3–CuOx system, where R=Ho, was investigated in air. The tie-line relationships of the system were determined. The Sr analog of the high Tc superconductor Ba2HoCu3O6+x was not observed in this system. Two ternary phases were found, namely, the "14–24" solid solution Sr14-xHoxCu24O41 and the "green phase" SrHo2CuO5. Holmium was found to substitute for the Sr site in the solid solution Sr14-xHoxCu24O41 up to the value of x5. The melting temperature range of this solid solution is from 975 to 1025°C, for x=0 to x=5, respectively. The green phase is isostructural to its Ba analog, BaHo2CuO5, and is orthorhombic with space group Pbnm and cell parameters a=7.0971(13) ?, b=12.0262(23) ?, and c=5.5849(12) ?. A comparison of the Ho system with reported systems of R=La, Nd, and Y indicated that a trend exists. The larger the lanthanide ions, the more complicated the phase diagrams, i.e., with a greater number of ternary phases/solid solutions. Despite similar ionic radii between Ho3+ and Y3+, the phase diagrams of these two systems are rather different. The green phase SrHo2CuO5 is not stable in the Y system.