Long-term stability of Hg-based cuprate superconducting thin films prepared from a fluoride precursor

Abstract

The long-term stability of superconducting properties of Hg-based cuprate thin films is presented. The mercury-based films were synthesized from an air-stable Ba-Ca-Cu-(O, F) precursor prepared by thermal evaporation from fluorides BaF 2 , CaF 2 and metallic Cu. The stability of the films prepared was studied using x-ray diffraction patterns and their electrical properties. The main features of superconducting transition (the onset and the midpoint temperature, as well as the width of transition) remained unchanged during 18 months, but the zero-resistivity critical temperature decreased from 117.5 K to 112 K (about 4%) due to an elongated low-resistivity tail. The good stability of the Hg-based cuprate thin films can be attributed to the dense character of our films that did not show any evident grain boundary morphology. Therefore, we assume that the main reason for the film degradation (as a rule localized at the grain boundaries) was eliminated.