THE EFFECT OF HEAT-TREATMENTS ON COBALT CONFIGURATION AND PHYSICAL-PROPERTIES OF YBA2(CU1-XCOX)3OY

YBa2(Cu1-xCox)3Oy (0 ≦ x ≦ 1 3) was prepared by two kinds of heat treatments: (a) slow cooling from 850°C in flowing O2 gas and (b) reducing at 800°C in flowing N2 gas followed by reoxidation in flowing O2 gas below 400°C. The crystal structure, superconducting properties, and Co configuration of the materials were examined by X-ray powder diffraction, electrical resistivity, and 57Co emission Mössbauer measurements. The orthorhombic phase was stabilized in the wide composition range (0 ≦ x ≦ 0.12) by the heat treatment (b) as well as in the Fe-substituted system. This extension of the orthorhombic phase region is due to the clustering of Co atoms in the Cu1O planes, which is developed by the heat treatment under a lower oxygen fugacity atmosphere at high temperature. © 1992.