OVERVIEW ON THE RECENT PROGRESS ON CHEVREL PHASES AND THE IMPACT ON THE DEVELOPMENT OF PbMo6S8 WIRES

The interest for the development of Chevrel phases superconducting wires originates from the high upper critical field of PbMo6S8 (PMS). Up to now, the critical current density J(C) of these wires has not reached a value required for industrial applications. However, large intra-grain J(C) has been observed indicating that the grain connections play a dominant role in the J(C) limitation. This behavior is similar to that of high-T-C oxides, where this limitation is thought to have an intrinsic origin related to their extremely short coherence lengths. But the coherence length of PMS lies between those of conventional superconductors and high-T-C materials. Therefore, it has been argued that an intrinsic granularity behavior is not expected for PMS and that the observed tendency towards granularity has another origin. Recent results about the phase stability, a possible structural transition and the degradation of the grain boundaries of PMS, point to different possible origins for the J(C) limitation. A critical analysis of these investigations and their impact on the performance of wires will be discussed.