RESISTIVITY BROADENING, UPPER CRITICAL FIELDS AND IRREVERSIBILITY LINES IN BULK PBMO6S8 AND SNMO6S8 CHEVREL-PHASE SUPERCONDUCTORS

Resistive (R(B,T)) transitions far both PbMo6S8 (PMS) and SnMo6S8 (SMS ) compounds were measured in applied magnetic fields. For both compoun ds, the pseudo upper critical field B-c2(T) lines determined at diffe rent constant resistance criteria show a deviation from the expected t hermodynamic B-c2(T). The deviation is more pronounced in the PMS samp le which has a smaller coherence length. The activation energy barrier s U-b(B) extracted from the Arrhenius plots of resistivity are lower f or PMS (U-b(9T) = 1570 K) than for SMS (U-b(ST) = 2250 K).