Effect of fluorine and cerium substitutions on the properties of the Tl2Ba2CaCu1.98Fe0.02O8 superconductor

Fluorine and cerium substituted Tl-2212 high-Tc superconductors were produced. X-ray diffraction, Mossbauer effect method, temperature measuring of the resistances and a.c. susceptibilities for all Tl2Ba2Ca1−yCeyCu1.98Fe0.02O8−x/2Fx (0 ⩽ x ⩽ 0.2 and 0 ⩽ y ⩽ 0.1) were applied. It was found that the cerium admixture does not affect significantly the Tl-2212 superconductor properties. Fluorine admixture alone appreciably affects the value of superconducting transition temperature. The biggest increase in Tc is 10 K and is realised for x = 0.10-0.20. Substituting admixtures are not clearly exhibited in Mossbauer parameters, i.e. do not influence Fe-O bonding tangibly.