New synthesis route of PbMo6S8 superconducting chevrel phase from ultrafine precursor mixtures:: II.: PbS, Mo6S8, and Mo powders

We have used a new ultrafine precursor, the Mo6S8 binary sulfide, and ultrafine PbS and Mo powders (similar to 0.05-0.5 mu m) to prepare an original mixture for PbMo6S8 synthesis. The reaction of PbMo6S8 formation occurs in a two-step process, at 600 and 800 degrees C, leading to a similar to 0.5 mu m grain size. chi(ac) measurements exhibit good superconducting quality (T-c approximate to 14 K) of the resulting PbMo6S8 phase. Additionally, we have perfected new synthesis processes of the Nisimilar to 2Mo6S8 and Lisimilar to 3Mo6S8 ternary Chevrel phases, precursors of the Mo6S8 compound. These syntheses are carried out by H2S gas sulfurization of the liquid or solid route and then reduction by H-2 gas over solid reaction. The Lisimilar to 3Mo6S8 phase was chosen because its cation deintercalation yields the smallest Mo6S8 grain size (similar to 0.3 mu m). (C) 1998 Elsevier Science Ltd.